Merge tag 'armsoc-defconfig' of git://git.kernel.org/pub/scm/linux/kernel/git/arm...

[thirdparty/kernel/stable.git] / drivers / pci / host / pci-hyperv.c

/*
 * Copyright (c) Microsoft Corporation.
 *
 * Author:
 *   Jake Oshins <jakeo@microsoft.com>
 *
 * This driver acts as a paravirtual front-end for PCI Express root buses.
 * When a PCI Express function (either an entire device or an SR-IOV
 * Virtual Function) is being passed through to the VM, this driver exposes
 * a new bus to the guest VM.  This is modeled as a root PCI bus because
 * no bridges are being exposed to the VM.  In fact, with a "Generation 2"
 * VM within Hyper-V, there may seem to be no PCI bus at all in the VM
 * until a device as been exposed using this driver.
 *
 * Each root PCI bus has its own PCI domain, which is called "Segment" in
 * the PCI Firmware Specifications.  Thus while each device passed through
 * to the VM using this front-end will appear at "device 0", the domain will
 * be unique.  Typically, each bus will have one PCI function on it, though
 * this driver does support more than one.
 *
 * In order to map the interrupts from the device through to the guest VM,
 * this driver also implements an IRQ Domain, which handles interrupts (either
 * MSI or MSI-X) associated with the functions on the bus.  As interrupts are
 * set up, torn down, or reaffined, this driver communicates with the
 * underlying hypervisor to adjust the mappings in the I/O MMU so that each
 * interrupt will be delivered to the correct virtual processor at the right
 * vector.  This driver does not support level-triggered (line-based)
 * interrupts, and will report that the Interrupt Line register in the
 * function's configuration space is zero.
 *
 * The rest of this driver mostly maps PCI concepts onto underlying Hyper-V
 * facilities.  For instance, the configuration space of a function exposed
 * by Hyper-V is mapped into a single page of memory space, and the
 * read and write handlers for config space must be aware of this mechanism.
 * Similarly, device setup and teardown involves messages sent to and from
 * the PCI back-end driver in Hyper-V.
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 as published
 * by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
 * NON INFRINGEMENT.  See the GNU General Public License for more
 * details.
 *
 */

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/pci.h>
#include <linux/semaphore.h>
#include <linux/irqdomain.h>
#include <asm/irqdomain.h>
#include <asm/apic.h>
#include <linux/msi.h>
#include <linux/hyperv.h>
#include <asm/mshyperv.h>

/*
 * Protocol versions. The low word is the minor version, the high word the
 * major version.
 */

#define PCI_MAKE_VERSION(major, minor) ((u32)(((major) << 16) | (major)))
#define PCI_MAJOR_VERSION(version) ((u32)(version) >> 16)
#define PCI_MINOR_VERSION(version) ((u32)(version) & 0xff)

enum {
        PCI_PROTOCOL_VERSION_1_1 = PCI_MAKE_VERSION(1, 1),
        PCI_PROTOCOL_VERSION_CURRENT = PCI_PROTOCOL_VERSION_1_1
};

#define PCI_CONFIG_MMIO_LENGTH  0x2000
#define CFG_PAGE_OFFSET 0x1000
#define CFG_PAGE_SIZE (PCI_CONFIG_MMIO_LENGTH - CFG_PAGE_OFFSET)

#define MAX_SUPPORTED_MSI_MESSAGES 0x400

/*
 * Message Types
 */

enum pci_message_type {
        /*
         * Version 1.1
         */
        PCI_MESSAGE_BASE                = 0x42490000,
        PCI_BUS_RELATIONS               = PCI_MESSAGE_BASE + 0,
        PCI_QUERY_BUS_RELATIONS         = PCI_MESSAGE_BASE + 1,
        PCI_POWER_STATE_CHANGE          = PCI_MESSAGE_BASE + 4,
        PCI_QUERY_RESOURCE_REQUIREMENTS = PCI_MESSAGE_BASE + 5,
        PCI_QUERY_RESOURCE_RESOURCES    = PCI_MESSAGE_BASE + 6,
        PCI_BUS_D0ENTRY                 = PCI_MESSAGE_BASE + 7,
        PCI_BUS_D0EXIT                  = PCI_MESSAGE_BASE + 8,
        PCI_READ_BLOCK                  = PCI_MESSAGE_BASE + 9,
        PCI_WRITE_BLOCK                 = PCI_MESSAGE_BASE + 0xA,
        PCI_EJECT                       = PCI_MESSAGE_BASE + 0xB,
        PCI_QUERY_STOP                  = PCI_MESSAGE_BASE + 0xC,
        PCI_REENABLE                    = PCI_MESSAGE_BASE + 0xD,
        PCI_QUERY_STOP_FAILED           = PCI_MESSAGE_BASE + 0xE,
        PCI_EJECTION_COMPLETE           = PCI_MESSAGE_BASE + 0xF,
        PCI_RESOURCES_ASSIGNED          = PCI_MESSAGE_BASE + 0x10,
        PCI_RESOURCES_RELEASED          = PCI_MESSAGE_BASE + 0x11,
        PCI_INVALIDATE_BLOCK            = PCI_MESSAGE_BASE + 0x12,
        PCI_QUERY_PROTOCOL_VERSION      = PCI_MESSAGE_BASE + 0x13,
        PCI_CREATE_INTERRUPT_MESSAGE    = PCI_MESSAGE_BASE + 0x14,
        PCI_DELETE_INTERRUPT_MESSAGE    = PCI_MESSAGE_BASE + 0x15,
        PCI_MESSAGE_MAXIMUM
};

/*
 * Structures defining the virtual PCI Express protocol.
 */

union pci_version {
        struct {
                u16 minor_version;
                u16 major_version;
        } parts;
        u32 version;
} __packed;

/*
 * Function numbers are 8-bits wide on Express, as interpreted through ARI,
 * which is all this driver does.  This representation is the one used in
 * Windows, which is what is expected when sending this back and forth with
 * the Hyper-V parent partition.
 */
union win_slot_encoding {
        struct {
                u32     func:8;
                u32     reserved:24;
        } bits;
        u32 slot;
} __packed;

/*
 * Pretty much as defined in the PCI Specifications.
 */
struct pci_function_description {
        u16     v_id;   /* vendor ID */
        u16     d_id;   /* device ID */
        u8      rev;
        u8      prog_intf;
        u8      subclass;
        u8      base_class;
        u32     subsystem_id;
        union win_slot_encoding win_slot;
        u32     ser;    /* serial number */
} __packed;

/**
 * struct hv_msi_desc
 * @vector:             IDT entry
 * @delivery_mode:      As defined in Intel's Programmer's
 *                      Reference Manual, Volume 3, Chapter 8.
 * @vector_count:       Number of contiguous entries in the
 *                      Interrupt Descriptor Table that are
 *                      occupied by this Message-Signaled
 *                      Interrupt. For "MSI", as first defined
 *                      in PCI 2.2, this can be between 1 and
 *                      32. For "MSI-X," as first defined in PCI
 *                      3.0, this must be 1, as each MSI-X table
 *                      entry would have its own descriptor.
 * @reserved:           Empty space
 * @cpu_mask:           All the target virtual processors.
 */
struct hv_msi_desc {
        u8      vector;
        u8      delivery_mode;
        u16     vector_count;
        u32     reserved;
        u64     cpu_mask;
} __packed;

/**
 * struct tran_int_desc
 * @reserved:           unused, padding
 * @vector_count:       same as in hv_msi_desc
 * @data:               This is the "data payload" value that is
 *                      written by the device when it generates
 *                      a message-signaled interrupt, either MSI
 *                      or MSI-X.
 * @address:            This is the address to which the data
 *                      payload is written on interrupt
 *                      generation.
 */
struct tran_int_desc {
        u16     reserved;
        u16     vector_count;
        u32     data;
        u64     address;
} __packed;

/*
 * A generic message format for virtual PCI.
 * Specific message formats are defined later in the file.
 */

struct pci_message {
        u32 type;
} __packed;

struct pci_child_message {
        struct pci_message message_type;
        union win_slot_encoding wslot;
} __packed;

struct pci_incoming_message {
        struct vmpacket_descriptor hdr;
        struct pci_message message_type;
} __packed;

struct pci_response {
        struct vmpacket_descriptor hdr;
        s32 status;                     /* negative values are failures */
} __packed;

struct pci_packet {
        void (*completion_func)(void *context, struct pci_response *resp,
                                int resp_packet_size);
        void *compl_ctxt;

        struct pci_message message[0];
};

/*
 * Specific message types supporting the PCI protocol.
 */

/*
 * Version negotiation message. Sent from the guest to the host.
 * The guest is free to try different versions until the host
 * accepts the version.
 *
 * pci_version: The protocol version requested.
 * is_last_attempt: If TRUE, this is the last version guest will request.
 * reservedz: Reserved field, set to zero.
 */

struct pci_version_request {
        struct pci_message message_type;
        enum pci_message_type protocol_version;
} __packed;

/*
 * Bus D0 Entry.  This is sent from the guest to the host when the virtual
 * bus (PCI Express port) is ready for action.
 */

struct pci_bus_d0_entry {
        struct pci_message message_type;
        u32 reserved;
        u64 mmio_base;
} __packed;

struct pci_bus_relations {
        struct pci_incoming_message incoming;
        u32 device_count;
        struct pci_function_description func[0];
} __packed;

struct pci_q_res_req_response {
        struct vmpacket_descriptor hdr;
        s32 status;                     /* negative values are failures */
        u32 probed_bar[6];
} __packed;

struct pci_set_power {
        struct pci_message message_type;
        union win_slot_encoding wslot;
        u32 power_state;                /* In Windows terms */
        u32 reserved;
} __packed;

struct pci_set_power_response {
        struct vmpacket_descriptor hdr;
        s32 status;                     /* negative values are failures */
        union win_slot_encoding wslot;
        u32 resultant_state;            /* In Windows terms */
        u32 reserved;
} __packed;

struct pci_resources_assigned {
        struct pci_message message_type;
        union win_slot_encoding wslot;
        u8 memory_range[0x14][6];       /* not used here */
        u32 msi_descriptors;
        u32 reserved[4];
} __packed;

struct pci_create_interrupt {
        struct pci_message message_type;
        union win_slot_encoding wslot;
        struct hv_msi_desc int_desc;
} __packed;

struct pci_create_int_response {
        struct pci_response response;
        u32 reserved;
        struct tran_int_desc int_desc;
} __packed;

struct pci_delete_interrupt {
        struct pci_message message_type;
        union win_slot_encoding wslot;
        struct tran_int_desc int_desc;
} __packed;

struct pci_dev_incoming {
        struct pci_incoming_message incoming;
        union win_slot_encoding wslot;
} __packed;

struct pci_eject_response {
        struct pci_message message_type;
        union win_slot_encoding wslot;
        u32 status;
} __packed;

static int pci_ring_size = (4 * PAGE_SIZE);

/*
 * Definitions or interrupt steering hypercall.
 */
#define HV_PARTITION_ID_SELF            ((u64)-1)
#define HVCALL_RETARGET_INTERRUPT       0x7e

struct retarget_msi_interrupt {
        u64     partition_id;           /* use "self" */
        u64     device_id;
        u32     source;                 /* 1 for MSI(-X) */
        u32     reserved1;
        u32     address;
        u32     data;
        u64     reserved2;
        u32     vector;
        u32     flags;
        u64     vp_mask;
} __packed;

/*
 * Driver specific state.
 */

enum hv_pcibus_state {
        hv_pcibus_init = 0,
        hv_pcibus_probed,
        hv_pcibus_installed,
        hv_pcibus_maximum
};

struct hv_pcibus_device {
        struct pci_sysdata sysdata;
        enum hv_pcibus_state state;
        atomic_t remove_lock;
        struct hv_device *hdev;
        resource_size_t low_mmio_space;
        resource_size_t high_mmio_space;
        struct resource *mem_config;
        struct resource *low_mmio_res;
        struct resource *high_mmio_res;
        struct completion *survey_event;
        struct completion remove_event;
        struct pci_bus *pci_bus;
        spinlock_t config_lock; /* Avoid two threads writing index page */
        spinlock_t device_list_lock;    /* Protect lists below */
        void __iomem *cfg_addr;

        struct semaphore enum_sem;
        struct list_head resources_for_children;

        struct list_head children;
        struct list_head dr_list;

        struct msi_domain_info msi_info;
        struct msi_controller msi_chip;
        struct irq_domain *irq_domain;
        struct retarget_msi_interrupt retarget_msi_interrupt_params;
        spinlock_t retarget_msi_interrupt_lock;
};

/*
 * Tracks "Device Relations" messages from the host, which must be both
 * processed in order and deferred so that they don't run in the context
 * of the incoming packet callback.
 */
struct hv_dr_work {
        struct work_struct wrk;
        struct hv_pcibus_device *bus;
};

struct hv_dr_state {
        struct list_head list_entry;
        u32 device_count;
        struct pci_function_description func[0];
};

enum hv_pcichild_state {
        hv_pcichild_init = 0,
        hv_pcichild_requirements,
        hv_pcichild_resourced,
        hv_pcichild_ejecting,
        hv_pcichild_maximum
};

enum hv_pcidev_ref_reason {
        hv_pcidev_ref_invalid = 0,
        hv_pcidev_ref_initial,
        hv_pcidev_ref_by_slot,
        hv_pcidev_ref_packet,
        hv_pcidev_ref_pnp,
        hv_pcidev_ref_childlist,
        hv_pcidev_irqdata,
        hv_pcidev_ref_max
};

struct hv_pci_dev {
        /* List protected by pci_rescan_remove_lock */
        struct list_head list_entry;
        atomic_t refs;
        enum hv_pcichild_state state;
        struct pci_function_description desc;
        bool reported_missing;
        struct hv_pcibus_device *hbus;
        struct work_struct wrk;

        /*
         * What would be observed if one wrote 0xFFFFFFFF to a BAR and then
         * read it back, for each of the BAR offsets within config space.
         */
        u32 probed_bar[6];
};

struct hv_pci_compl {
        struct completion host_event;
        s32 completion_status;
};

/**
 * hv_pci_generic_compl() - Invoked for a completion packet
 * @context:            Set up by the sender of the packet.
 * @resp:               The response packet
 * @resp_packet_size:   Size in bytes of the packet
 *
 * This function is used to trigger an event and report status
 * for any message for which the completion packet contains a
 * status and nothing else.
 */
static void hv_pci_generic_compl(void *context, struct pci_response *resp,
                                 int resp_packet_size)
{
        struct hv_pci_compl *comp_pkt = context;

        if (resp_packet_size >= offsetofend(struct pci_response, status))
                comp_pkt->completion_status = resp->status;
        else
                comp_pkt->completion_status = -1;

        complete(&comp_pkt->host_event);
}

static struct hv_pci_dev *get_pcichild_wslot(struct hv_pcibus_device *hbus,
                                                u32 wslot);
static void get_pcichild(struct hv_pci_dev *hv_pcidev,
                         enum hv_pcidev_ref_reason reason);
static void put_pcichild(struct hv_pci_dev *hv_pcidev,
                         enum hv_pcidev_ref_reason reason);

static void get_hvpcibus(struct hv_pcibus_device *hv_pcibus);
static void put_hvpcibus(struct hv_pcibus_device *hv_pcibus);

/**
 * devfn_to_wslot() - Convert from Linux PCI slot to Windows
 * @devfn:      The Linux representation of PCI slot
 *
 * Windows uses a slightly different representation of PCI slot.
 *
 * Return: The Windows representation
 */
static u32 devfn_to_wslot(int devfn)
{
        union win_slot_encoding wslot;

        wslot.slot = 0;
        wslot.bits.func = PCI_SLOT(devfn) | (PCI_FUNC(devfn) << 5);

        return wslot.slot;
}

/**
 * wslot_to_devfn() - Convert from Windows PCI slot to Linux
 * @wslot:      The Windows representation of PCI slot
 *
 * Windows uses a slightly different representation of PCI slot.
 *
 * Return: The Linux representation
 */
static int wslot_to_devfn(u32 wslot)
{
        union win_slot_encoding slot_no;

        slot_no.slot = wslot;
        return PCI_DEVFN(0, slot_no.bits.func);
}

/*
 * PCI Configuration Space for these root PCI buses is implemented as a pair
 * of pages in memory-mapped I/O space.  Writing to the first page chooses
 * the PCI function being written or read.  Once the first page has been
 * written to, the following page maps in the entire configuration space of
 * the function.
 */

/**
 * _hv_pcifront_read_config() - Internal PCI config read
 * @hpdev:      The PCI driver's representation of the device
 * @where:      Offset within config space
 * @size:       Size of the transfer
 * @val:        Pointer to the buffer receiving the data
 */
static void _hv_pcifront_read_config(struct hv_pci_dev *hpdev, int where,
                                     int size, u32 *val)
{
        unsigned long flags;
        void __iomem *addr = hpdev->hbus->cfg_addr + CFG_PAGE_OFFSET + where;

        /*
         * If the attempt is to read the IDs or the ROM BAR, simulate that.
         */
        if (where + size <= PCI_COMMAND) {
                memcpy(val, ((u8 *)&hpdev->desc.v_id) + where, size);
        } else if (where >= PCI_CLASS_REVISION && where + size <=
                   PCI_CACHE_LINE_SIZE) {
                memcpy(val, ((u8 *)&hpdev->desc.rev) + where -
                       PCI_CLASS_REVISION, size);
        } else if (where >= PCI_SUBSYSTEM_VENDOR_ID && where + size <=
                   PCI_ROM_ADDRESS) {
                memcpy(val, (u8 *)&hpdev->desc.subsystem_id + where -
                       PCI_SUBSYSTEM_VENDOR_ID, size);
        } else if (where >= PCI_ROM_ADDRESS && where + size <=
                   PCI_CAPABILITY_LIST) {
                /* ROM BARs are unimplemented */
                *val = 0;
        } else if (where >= PCI_INTERRUPT_LINE && where + size <=
                   PCI_INTERRUPT_PIN) {
                /*
                 * Interrupt Line and Interrupt PIN are hard-wired to zero
                 * because this front-end only supports message-signaled
                 * interrupts.
                 */
                *val = 0;
        } else if (where + size <= CFG_PAGE_SIZE) {
                spin_lock_irqsave(&hpdev->hbus->config_lock, flags);
                /* Choose the function to be read. (See comment above) */
                writel(hpdev->desc.win_slot.slot, hpdev->hbus->cfg_addr);
                /* Make sure the function was chosen before we start reading. */
                mb();
                /* Read from that function's config space. */
                switch (size) {
                case 1:
                        *val = readb(addr);
                        break;
                case 2:
                        *val = readw(addr);
                        break;
                default:
                        *val = readl(addr);
                        break;
                }
                /*
                 * Make sure the write was done before we release the spinlock
                 * allowing consecutive reads/writes.
                 */
                mb();
                spin_unlock_irqrestore(&hpdev->hbus->config_lock, flags);
        } else {
                dev_err(&hpdev->hbus->hdev->device,
                        "Attempt to read beyond a function's config space.\n");
        }
}

/**
 * _hv_pcifront_write_config() - Internal PCI config write
 * @hpdev:      The PCI driver's representation of the device
 * @where:      Offset within config space
 * @size:       Size of the transfer
 * @val:        The data being transferred
 */
static void _hv_pcifront_write_config(struct hv_pci_dev *hpdev, int where,
                                      int size, u32 val)
{
        unsigned long flags;
        void __iomem *addr = hpdev->hbus->cfg_addr + CFG_PAGE_OFFSET + where;

        if (where >= PCI_SUBSYSTEM_VENDOR_ID &&
            where + size <= PCI_CAPABILITY_LIST) {
                /* SSIDs and ROM BARs are read-only */
        } else if (where >= PCI_COMMAND && where + size <= CFG_PAGE_SIZE) {
                spin_lock_irqsave(&hpdev->hbus->config_lock, flags);
                /* Choose the function to be written. (See comment above) */
                writel(hpdev->desc.win_slot.slot, hpdev->hbus->cfg_addr);
                /* Make sure the function was chosen before we start writing. */
                wmb();
                /* Write to that function's config space. */
                switch (size) {
                case 1:
                        writeb(val, addr);
                        break;
                case 2:
                        writew(val, addr);
                        break;
                default:
                        writel(val, addr);
                        break;
                }
                /*
                 * Make sure the write was done before we release the spinlock
                 * allowing consecutive reads/writes.
                 */
                mb();
                spin_unlock_irqrestore(&hpdev->hbus->config_lock, flags);
        } else {
                dev_err(&hpdev->hbus->hdev->device,
                        "Attempt to write beyond a function's config space.\n");
        }
}

/**
 * hv_pcifront_read_config() - Read configuration space
 * @bus: PCI Bus structure
 * @devfn: Device/function
 * @where: Offset from base
 * @size: Byte/word/dword
 * @val: Value to be read
 *
 * Return: PCIBIOS_SUCCESSFUL on success
 *         PCIBIOS_DEVICE_NOT_FOUND on failure
 */
static int hv_pcifront_read_config(struct pci_bus *bus, unsigned int devfn,
                                   int where, int size, u32 *val)
{
        struct hv_pcibus_device *hbus =
                container_of(bus->sysdata, struct hv_pcibus_device, sysdata);
        struct hv_pci_dev *hpdev;

        hpdev = get_pcichild_wslot(hbus, devfn_to_wslot(devfn));
        if (!hpdev)
                return PCIBIOS_DEVICE_NOT_FOUND;

        _hv_pcifront_read_config(hpdev, where, size, val);

        put_pcichild(hpdev, hv_pcidev_ref_by_slot);
        return PCIBIOS_SUCCESSFUL;
}

/**
 * hv_pcifront_write_config() - Write configuration space
 * @bus: PCI Bus structure
 * @devfn: Device/function
 * @where: Offset from base
 * @size: Byte/word/dword
 * @val: Value to be written to device
 *
 * Return: PCIBIOS_SUCCESSFUL on success
 *         PCIBIOS_DEVICE_NOT_FOUND on failure
 */
static int hv_pcifront_write_config(struct pci_bus *bus, unsigned int devfn,
                                    int where, int size, u32 val)
{
        struct hv_pcibus_device *hbus =
            container_of(bus->sysdata, struct hv_pcibus_device, sysdata);
        struct hv_pci_dev *hpdev;

        hpdev = get_pcichild_wslot(hbus, devfn_to_wslot(devfn));
        if (!hpdev)
                return PCIBIOS_DEVICE_NOT_FOUND;

        _hv_pcifront_write_config(hpdev, where, size, val);

        put_pcichild(hpdev, hv_pcidev_ref_by_slot);
        return PCIBIOS_SUCCESSFUL;
}

/* PCIe operations */
static struct pci_ops hv_pcifront_ops = {
        .read  = hv_pcifront_read_config,
        .write = hv_pcifront_write_config,
};

/* Interrupt management hooks */
static void hv_int_desc_free(struct hv_pci_dev *hpdev,
                             struct tran_int_desc *int_desc)
{
        struct pci_delete_interrupt *int_pkt;
        struct {
                struct pci_packet pkt;
                u8 buffer[sizeof(struct pci_delete_interrupt)];
        } ctxt;

        memset(&ctxt, 0, sizeof(ctxt));
        int_pkt = (struct pci_delete_interrupt *)&ctxt.pkt.message;
        int_pkt->message_type.type =
                PCI_DELETE_INTERRUPT_MESSAGE;
        int_pkt->wslot.slot = hpdev->desc.win_slot.slot;
        int_pkt->int_desc = *int_desc;
        vmbus_sendpacket(hpdev->hbus->hdev->channel, int_pkt, sizeof(*int_pkt),
                         (unsigned long)&ctxt.pkt, VM_PKT_DATA_INBAND, 0);
        kfree(int_desc);
}

/**
 * hv_msi_free() - Free the MSI.
 * @domain:     The interrupt domain pointer
 * @info:       Extra MSI-related context
 * @irq:        Identifies the IRQ.
 *
 * The Hyper-V parent partition and hypervisor are tracking the
 * messages that are in use, keeping the interrupt redirection
 * table up to date.  This callback sends a message that frees
 * the IRT entry and related tracking nonsense.
 */
static void hv_msi_free(struct irq_domain *domain, struct msi_domain_info *info,
                        unsigned int irq)
{
        struct hv_pcibus_device *hbus;
        struct hv_pci_dev *hpdev;
        struct pci_dev *pdev;
        struct tran_int_desc *int_desc;
        struct irq_data *irq_data = irq_domain_get_irq_data(domain, irq);
        struct msi_desc *msi = irq_data_get_msi_desc(irq_data);

        pdev = msi_desc_to_pci_dev(msi);
        hbus = info->data;
        int_desc = irq_data_get_irq_chip_data(irq_data);
        if (!int_desc)
                return;

        irq_data->chip_data = NULL;
        hpdev = get_pcichild_wslot(hbus, devfn_to_wslot(pdev->devfn));
        if (!hpdev) {
                kfree(int_desc);
                return;
        }

        hv_int_desc_free(hpdev, int_desc);
        put_pcichild(hpdev, hv_pcidev_ref_by_slot);
}

static int hv_set_affinity(struct irq_data *data, const struct cpumask *dest,
                           bool force)
{
        struct irq_data *parent = data->parent_data;

        return parent->chip->irq_set_affinity(parent, dest, force);
}

static void hv_irq_mask(struct irq_data *data)
{
        pci_msi_mask_irq(data);
}

/**
 * hv_irq_unmask() - "Unmask" the IRQ by setting its current
 * affinity.
 * @data:       Describes the IRQ
 *
 * Build new a destination for the MSI and make a hypercall to
 * update the Interrupt Redirection Table. "Device Logical ID"
 * is built out of this PCI bus's instance GUID and the function
 * number of the device.
 */
static void hv_irq_unmask(struct irq_data *data)
{
        struct msi_desc *msi_desc = irq_data_get_msi_desc(data);
        struct irq_cfg *cfg = irqd_cfg(data);
        struct retarget_msi_interrupt *params;
        struct hv_pcibus_device *hbus;
        struct cpumask *dest;
        struct pci_bus *pbus;
        struct pci_dev *pdev;
        int cpu;
        unsigned long flags;

        dest = irq_data_get_affinity_mask(data);
        pdev = msi_desc_to_pci_dev(msi_desc);
        pbus = pdev->bus;
        hbus = container_of(pbus->sysdata, struct hv_pcibus_device, sysdata);

        spin_lock_irqsave(&hbus->retarget_msi_interrupt_lock, flags);

        params = &hbus->retarget_msi_interrupt_params;
        memset(params, 0, sizeof(*params));
        params->partition_id = HV_PARTITION_ID_SELF;
        params->source = 1; /* MSI(-X) */
        params->address = msi_desc->msg.address_lo;
        params->data = msi_desc->msg.data;
        params->device_id = (hbus->hdev->dev_instance.b[5] << 24) |
                           (hbus->hdev->dev_instance.b[4] << 16) |
                           (hbus->hdev->dev_instance.b[7] << 8) |
                           (hbus->hdev->dev_instance.b[6] & 0xf8) |
                           PCI_FUNC(pdev->devfn);
        params->vector = cfg->vector;

        for_each_cpu_and(cpu, dest, cpu_online_mask)
                params->vp_mask |= (1ULL << vmbus_cpu_number_to_vp_number(cpu));

        hv_do_hypercall(HVCALL_RETARGET_INTERRUPT, params, NULL);

        spin_unlock_irqrestore(&hbus->retarget_msi_interrupt_lock, flags);

        pci_msi_unmask_irq(data);
}

struct compose_comp_ctxt {
        struct hv_pci_compl comp_pkt;
        struct tran_int_desc int_desc;
};

static void hv_pci_compose_compl(void *context, struct pci_response *resp,
                                 int resp_packet_size)
{
        struct compose_comp_ctxt *comp_pkt = context;
        struct pci_create_int_response *int_resp =
                (struct pci_create_int_response *)resp;

        comp_pkt->comp_pkt.completion_status = resp->status;
        comp_pkt->int_desc = int_resp->int_desc;
        complete(&comp_pkt->comp_pkt.host_event);
}

/**
 * hv_compose_msi_msg() - Supplies a valid MSI address/data
 * @data:       Everything about this MSI
 * @msg:        Buffer that is filled in by this function
 *
 * This function unpacks the IRQ looking for target CPU set, IDT
 * vector and mode and sends a message to the parent partition
 * asking for a mapping for that tuple in this partition.  The
 * response supplies a data value and address to which that data
 * should be written to trigger that interrupt.
 */
static void hv_compose_msi_msg(struct irq_data *data, struct msi_msg *msg)
{
        struct irq_cfg *cfg = irqd_cfg(data);
        struct hv_pcibus_device *hbus;
        struct hv_pci_dev *hpdev;
        struct pci_bus *pbus;
        struct pci_dev *pdev;
        struct pci_create_interrupt *int_pkt;
        struct compose_comp_ctxt comp;
        struct tran_int_desc *int_desc;
        struct cpumask *affinity;
        struct {
                struct pci_packet pkt;
                u8 buffer[sizeof(struct pci_create_interrupt)];
        } ctxt;
        int cpu;
        int ret;

        pdev = msi_desc_to_pci_dev(irq_data_get_msi_desc(data));
        pbus = pdev->bus;
        hbus = container_of(pbus->sysdata, struct hv_pcibus_device, sysdata);
        hpdev = get_pcichild_wslot(hbus, devfn_to_wslot(pdev->devfn));
        if (!hpdev)
                goto return_null_message;

        /* Free any previous message that might have already been composed. */
        if (data->chip_data) {
                int_desc = data->chip_data;
                data->chip_data = NULL;
                hv_int_desc_free(hpdev, int_desc);
        }

        int_desc = kzalloc(sizeof(*int_desc), GFP_KERNEL);
        if (!int_desc)
                goto drop_reference;

        memset(&ctxt, 0, sizeof(ctxt));
        init_completion(&comp.comp_pkt.host_event);
        ctxt.pkt.completion_func = hv_pci_compose_compl;
        ctxt.pkt.compl_ctxt = &comp;
        int_pkt = (struct pci_create_interrupt *)&ctxt.pkt.message;
        int_pkt->message_type.type = PCI_CREATE_INTERRUPT_MESSAGE;
        int_pkt->wslot.slot = hpdev->desc.win_slot.slot;
        int_pkt->int_desc.vector = cfg->vector;
        int_pkt->int_desc.vector_count = 1;
        int_pkt->int_desc.delivery_mode =
                (apic->irq_delivery_mode == dest_LowestPrio) ? 1 : 0;

        /*
         * This bit doesn't have to work on machines with more than 64
         * processors because Hyper-V only supports 64 in a guest.
         */
        affinity = irq_data_get_affinity_mask(data);
        for_each_cpu_and(cpu, affinity, cpu_online_mask) {
                int_pkt->int_desc.cpu_mask |=
                        (1ULL << vmbus_cpu_number_to_vp_number(cpu));
        }

        ret = vmbus_sendpacket(hpdev->hbus->hdev->channel, int_pkt,
                               sizeof(*int_pkt), (unsigned long)&ctxt.pkt,
                               VM_PKT_DATA_INBAND,
                               VMBUS_DATA_PACKET_FLAG_COMPLETION_REQUESTED);
        if (ret)
                goto free_int_desc;

        wait_for_completion(&comp.comp_pkt.host_event);

        if (comp.comp_pkt.completion_status < 0) {
                dev_err(&hbus->hdev->device,
                        "Request for interrupt failed: 0x%x",
                        comp.comp_pkt.completion_status);
                goto free_int_desc;
        }

        /*
         * Record the assignment so that this can be unwound later. Using
         * irq_set_chip_data() here would be appropriate, but the lock it takes
         * is already held.
         */
        *int_desc = comp.int_desc;
        data->chip_data = int_desc;

        /* Pass up the result. */
        msg->address_hi = comp.int_desc.address >> 32;
        msg->address_lo = comp.int_desc.address & 0xffffffff;
        msg->data = comp.int_desc.data;

        put_pcichild(hpdev, hv_pcidev_ref_by_slot);
        return;

free_int_desc:
        kfree(int_desc);
drop_reference:
        put_pcichild(hpdev, hv_pcidev_ref_by_slot);
return_null_message:
        msg->address_hi = 0;
        msg->address_lo = 0;
        msg->data = 0;
}

/* HW Interrupt Chip Descriptor */
static struct irq_chip hv_msi_irq_chip = {
        .name                   = "Hyper-V PCIe MSI",
        .irq_compose_msi_msg    = hv_compose_msi_msg,
        .irq_set_affinity       = hv_set_affinity,
        .irq_ack                = irq_chip_ack_parent,
        .irq_mask               = hv_irq_mask,
        .irq_unmask             = hv_irq_unmask,
};

static irq_hw_number_t hv_msi_domain_ops_get_hwirq(struct msi_domain_info *info,
                                                   msi_alloc_info_t *arg)
{
        return arg->msi_hwirq;
}

static struct msi_domain_ops hv_msi_ops = {
        .get_hwirq      = hv_msi_domain_ops_get_hwirq,
        .msi_prepare    = pci_msi_prepare,
        .set_desc       = pci_msi_set_desc,
        .msi_free       = hv_msi_free,
};

/**
 * hv_pcie_init_irq_domain() - Initialize IRQ domain
 * @hbus:       The root PCI bus
 *
 * This function creates an IRQ domain which will be used for
 * interrupts from devices that have been passed through.  These
 * devices only support MSI and MSI-X, not line-based interrupts
 * or simulations of line-based interrupts through PCIe's
 * fabric-layer messages.  Because interrupts are remapped, we
 * can support multi-message MSI here.
 *
 * Return: '0' on success and error value on failure
 */
static int hv_pcie_init_irq_domain(struct hv_pcibus_device *hbus)
{
        hbus->msi_info.chip = &hv_msi_irq_chip;
        hbus->msi_info.ops = &hv_msi_ops;
        hbus->msi_info.flags = (MSI_FLAG_USE_DEF_DOM_OPS |
                MSI_FLAG_USE_DEF_CHIP_OPS | MSI_FLAG_MULTI_PCI_MSI |
                MSI_FLAG_PCI_MSIX);
        hbus->msi_info.handler = handle_edge_irq;
        hbus->msi_info.handler_name = "edge";
        hbus->msi_info.data = hbus;
        hbus->irq_domain = pci_msi_create_irq_domain(hbus->sysdata.fwnode,
                                                     &hbus->msi_info,
                                                     x86_vector_domain);
        if (!hbus->irq_domain) {
                dev_err(&hbus->hdev->device,
                        "Failed to build an MSI IRQ domain\n");
                return -ENODEV;
        }

        return 0;
}

/**
 * get_bar_size() - Get the address space consumed by a BAR
 * @bar_val:    Value that a BAR returned after -1 was written
 *              to it.
 *
 * This function returns the size of the BAR, rounded up to 1
 * page.  It has to be rounded up because the hypervisor's page
 * table entry that maps the BAR into the VM can't specify an
 * offset within a page.  The invariant is that the hypervisor
 * must place any BARs of smaller than page length at the
 * beginning of a page.
 *
 * Return:      Size in bytes of the consumed MMIO space.
 */
static u64 get_bar_size(u64 bar_val)
{
        return round_up((1 + ~(bar_val & PCI_BASE_ADDRESS_MEM_MASK)),
                        PAGE_SIZE);
}

/**
 * survey_child_resources() - Total all MMIO requirements
 * @hbus:       Root PCI bus, as understood by this driver
 */
static void survey_child_resources(struct hv_pcibus_device *hbus)
{
        struct list_head *iter;
        struct hv_pci_dev *hpdev;
        resource_size_t bar_size = 0;
        unsigned long flags;
        struct completion *event;
        u64 bar_val;
        int i;

        /* If nobody is waiting on the answer, don't compute it. */
        event = xchg(&hbus->survey_event, NULL);
        if (!event)
                return;

        /* If the answer has already been computed, go with it. */
        if (hbus->low_mmio_space || hbus->high_mmio_space) {
                complete(event);
                return;
        }

        spin_lock_irqsave(&hbus->device_list_lock, flags);

        /*
         * Due to an interesting quirk of the PCI spec, all memory regions
         * for a child device are a power of 2 in size and aligned in memory,
         * so it's sufficient to just add them up without tracking alignment.
         */
        list_for_each(iter, &hbus->children) {
                hpdev = container_of(iter, struct hv_pci_dev, list_entry);
                for (i = 0; i < 6; i++) {
                        if (hpdev->probed_bar[i] & PCI_BASE_ADDRESS_SPACE_IO)
                                dev_err(&hbus->hdev->device,
                                        "There's an I/O BAR in this list!\n");

                        if (hpdev->probed_bar[i] != 0) {
                                /*
                                 * A probed BAR has all the upper bits set that
                                 * can be changed.
                                 */

                                bar_val = hpdev->probed_bar[i];
                                if (bar_val & PCI_BASE_ADDRESS_MEM_TYPE_64)
                                        bar_val |=
                                        ((u64)hpdev->probed_bar[++i] << 32);
                                else
                                        bar_val |= 0xffffffff00000000ULL;

                                bar_size = get_bar_size(bar_val);

                                if (bar_val & PCI_BASE_ADDRESS_MEM_TYPE_64)
                                        hbus->high_mmio_space += bar_size;
                                else
                                        hbus->low_mmio_space += bar_size;
                        }
                }
        }

        spin_unlock_irqrestore(&hbus->device_list_lock, flags);
        complete(event);
}

/**
 * prepopulate_bars() - Fill in BARs with defaults
 * @hbus:       Root PCI bus, as understood by this driver
 *
 * The core PCI driver code seems much, much happier if the BARs
 * for a device have values upon first scan. So fill them in.
 * The algorithm below works down from large sizes to small,
 * attempting to pack the assignments optimally. The assumption,
 * enforced in other parts of the code, is that the beginning of
 * the memory-mapped I/O space will be aligned on the largest
 * BAR size.
 */
static void prepopulate_bars(struct hv_pcibus_device *hbus)
{
        resource_size_t high_size = 0;
        resource_size_t low_size = 0;
        resource_size_t high_base = 0;
        resource_size_t low_base = 0;
        resource_size_t bar_size;
        struct hv_pci_dev *hpdev;
        struct list_head *iter;
        unsigned long flags;
        u64 bar_val;
        u32 command;
        bool high;
        int i;

        if (hbus->low_mmio_space) {
                low_size = 1ULL << (63 - __builtin_clzll(hbus->low_mmio_space));
                low_base = hbus->low_mmio_res->start;
        }

        if (hbus->high_mmio_space) {
                high_size = 1ULL <<
                        (63 - __builtin_clzll(hbus->high_mmio_space));
                high_base = hbus->high_mmio_res->start;
        }

        spin_lock_irqsave(&hbus->device_list_lock, flags);

        /* Pick addresses for the BARs. */
        do {
                list_for_each(iter, &hbus->children) {
                        hpdev = container_of(iter, struct hv_pci_dev,
                                             list_entry);
                        for (i = 0; i < 6; i++) {
                                bar_val = hpdev->probed_bar[i];
                                if (bar_val == 0)
                                        continue;
                                high = bar_val & PCI_BASE_ADDRESS_MEM_TYPE_64;
                                if (high) {
                                        bar_val |=
                                                ((u64)hpdev->probed_bar[i + 1]
                                                 << 32);
                                } else {
                                        bar_val |= 0xffffffffULL << 32;
                                }
                                bar_size = get_bar_size(bar_val);
                                if (high) {
                                        if (high_size != bar_size) {
                                                i++;
                                                continue;
                                        }
                                        _hv_pcifront_write_config(hpdev,
                                                PCI_BASE_ADDRESS_0 + (4 * i),
                                                4,
                                                (u32)(high_base & 0xffffff00));
                                        i++;
                                        _hv_pcifront_write_config(hpdev,
                                                PCI_BASE_ADDRESS_0 + (4 * i),
                                                4, (u32)(high_base >> 32));
                                        high_base += bar_size;
                                } else {
                                        if (low_size != bar_size)
                                                continue;
                                        _hv_pcifront_write_config(hpdev,
                                                PCI_BASE_ADDRESS_0 + (4 * i),
                                                4,
                                                (u32)(low_base & 0xffffff00));
                                        low_base += bar_size;
                                }
                        }
                        if (high_size <= 1 && low_size <= 1) {
                                /* Set the memory enable bit. */
                                _hv_pcifront_read_config(hpdev, PCI_COMMAND, 2,
                                                         &command);
                                command |= PCI_COMMAND_MEMORY;
                                _hv_pcifront_write_config(hpdev, PCI_COMMAND, 2,
                                                          command);
                                break;
                        }
                }

                high_size >>= 1;
                low_size >>= 1;
        }  while (high_size || low_size);

        spin_unlock_irqrestore(&hbus->device_list_lock, flags);
}

/**
 * create_root_hv_pci_bus() - Expose a new root PCI bus
 * @hbus:       Root PCI bus, as understood by this driver
 *
 * Return: 0 on success, -errno on failure
 */
static int create_root_hv_pci_bus(struct hv_pcibus_device *hbus)
{
        /* Register the device */
        hbus->pci_bus = pci_create_root_bus(&hbus->hdev->device,
                                            0, /* bus number is always zero */
                                            &hv_pcifront_ops,
                                            &hbus->sysdata,
                                            &hbus->resources_for_children);
        if (!hbus->pci_bus)
                return -ENODEV;

        hbus->pci_bus->msi = &hbus->msi_chip;
        hbus->pci_bus->msi->dev = &hbus->hdev->device;

        pci_scan_child_bus(hbus->pci_bus);
        pci_bus_assign_resources(hbus->pci_bus);
        pci_bus_add_devices(hbus->pci_bus);
        hbus->state = hv_pcibus_installed;
        return 0;
}

struct q_res_req_compl {
        struct completion host_event;
        struct hv_pci_dev *hpdev;
};

/**
 * q_resource_requirements() - Query Resource Requirements
 * @context:            The completion context.
 * @resp:               The response that came from the host.
 * @resp_packet_size:   The size in bytes of resp.
 *
 * This function is invoked on completion of a Query Resource
 * Requirements packet.
 */
static void q_resource_requirements(void *context, struct pci_response *resp,
                                    int resp_packet_size)
{
        struct q_res_req_compl *completion = context;
        struct pci_q_res_req_response *q_res_req =
                (struct pci_q_res_req_response *)resp;
        int i;

        if (resp->status < 0) {
                dev_err(&completion->hpdev->hbus->hdev->device,
                        "query resource requirements failed: %x\n",
                        resp->status);
        } else {
                for (i = 0; i < 6; i++) {
                        completion->hpdev->probed_bar[i] =
                                q_res_req->probed_bar[i];
                }
        }

        complete(&completion->host_event);
}

static void get_pcichild(struct hv_pci_dev *hpdev,
                            enum hv_pcidev_ref_reason reason)
{
        atomic_inc(&hpdev->refs);
}

static void put_pcichild(struct hv_pci_dev *hpdev,
                            enum hv_pcidev_ref_reason reason)
{
        if (atomic_dec_and_test(&hpdev->refs))
                kfree(hpdev);
}

/**
 * new_pcichild_device() - Create a new child device
 * @hbus:       The internal struct tracking this root PCI bus.
 * @desc:       The information supplied so far from the host
 *              about the device.
 *
 * This function creates the tracking structure for a new child
 * device and kicks off the process of figuring out what it is.
 *
 * Return: Pointer to the new tracking struct
 */
static struct hv_pci_dev *new_pcichild_device(struct hv_pcibus_device *hbus,
                struct pci_function_description *desc)
{
        struct hv_pci_dev *hpdev;
        struct pci_child_message *res_req;
        struct q_res_req_compl comp_pkt;
        struct {
                struct pci_packet init_packet;
                u8 buffer[sizeof(struct pci_child_message)];
        } pkt;
        unsigned long flags;
        int ret;

        hpdev = kzalloc(sizeof(*hpdev), GFP_ATOMIC);
        if (!hpdev)
                return NULL;

        hpdev->hbus = hbus;

        memset(&pkt, 0, sizeof(pkt));
        init_completion(&comp_pkt.host_event);
        comp_pkt.hpdev = hpdev;
        pkt.init_packet.compl_ctxt = &comp_pkt;
        pkt.init_packet.completion_func = q_resource_requirements;
        res_req = (struct pci_child_message *)&pkt.init_packet.message;
        res_req->message_type.type = PCI_QUERY_RESOURCE_REQUIREMENTS;
        res_req->wslot.slot = desc->win_slot.slot;

        ret = vmbus_sendpacket(hbus->hdev->channel, res_req,
                               sizeof(struct pci_child_message),
                               (unsigned long)&pkt.init_packet,
                               VM_PKT_DATA_INBAND,
                               VMBUS_DATA_PACKET_FLAG_COMPLETION_REQUESTED);
        if (ret)
                goto error;

        wait_for_completion(&comp_pkt.host_event);

        hpdev->desc = *desc;
        get_pcichild(hpdev, hv_pcidev_ref_initial);
        get_pcichild(hpdev, hv_pcidev_ref_childlist);
        spin_lock_irqsave(&hbus->device_list_lock, flags);
        list_add_tail(&hpdev->list_entry, &hbus->children);
        spin_unlock_irqrestore(&hbus->device_list_lock, flags);
        return hpdev;

error:
        kfree(hpdev);
        return NULL;
}

/**
 * get_pcichild_wslot() - Find device from slot
 * @hbus:       Root PCI bus, as understood by this driver
 * @wslot:      Location on the bus
 *
 * This function looks up a PCI device and returns the internal
 * representation of it.  It acquires a reference on it, so that
 * the device won't be deleted while somebody is using it.  The
 * caller is responsible for calling put_pcichild() to release
 * this reference.
 *
 * Return:      Internal representation of a PCI device
 */
static struct hv_pci_dev *get_pcichild_wslot(struct hv_pcibus_device *hbus,
                                             u32 wslot)
{
        unsigned long flags;
        struct hv_pci_dev *iter, *hpdev = NULL;

        spin_lock_irqsave(&hbus->device_list_lock, flags);
        list_for_each_entry(iter, &hbus->children, list_entry) {
                if (iter->desc.win_slot.slot == wslot) {
                        hpdev = iter;
                        get_pcichild(hpdev, hv_pcidev_ref_by_slot);
                        break;
                }
        }
        spin_unlock_irqrestore(&hbus->device_list_lock, flags);

        return hpdev;
}

/**
 * pci_devices_present_work() - Handle new list of child devices
 * @work:       Work struct embedded in struct hv_dr_work
 *
 * "Bus Relations" is the Windows term for "children of this
 * bus."  The terminology is preserved here for people trying to
 * debug the interaction between Hyper-V and Linux.  This
 * function is called when the parent partition reports a list
 * of functions that should be observed under this PCI Express
 * port (bus).
 *
 * This function updates the list, and must tolerate being
 * called multiple times with the same information.  The typical
 * number of child devices is one, with very atypical cases
 * involving three or four, so the algorithms used here can be
 * simple and inefficient.
 *
 * It must also treat the omission of a previously observed device as
 * notification that the device no longer exists.
 *
 * Note that this function is a work item, and it may not be
 * invoked in the order that it was queued.  Back to back
 * updates of the list of present devices may involve queuing
 * multiple work items, and this one may run before ones that
 * were sent later. As such, this function only does something
 * if is the last one in the queue.
 */
static void pci_devices_present_work(struct work_struct *work)
{
        u32 child_no;
        bool found;
        struct list_head *iter;
        struct pci_function_description *new_desc;
        struct hv_pci_dev *hpdev;
        struct hv_pcibus_device *hbus;
        struct list_head removed;
        struct hv_dr_work *dr_wrk;
        struct hv_dr_state *dr = NULL;
        unsigned long flags;

        dr_wrk = container_of(work, struct hv_dr_work, wrk);
        hbus = dr_wrk->bus;
        kfree(dr_wrk);

        INIT_LIST_HEAD(&removed);

        if (down_interruptible(&hbus->enum_sem)) {
                put_hvpcibus(hbus);
                return;
        }

        /* Pull this off the queue and process it if it was the last one. */
        spin_lock_irqsave(&hbus->device_list_lock, flags);
        while (!list_empty(&hbus->dr_list)) {
                dr = list_first_entry(&hbus->dr_list, struct hv_dr_state,
                                      list_entry);
                list_del(&dr->list_entry);

                /* Throw this away if the list still has stuff in it. */
                if (!list_empty(&hbus->dr_list)) {
                        kfree(dr);
                        continue;
                }
        }
        spin_unlock_irqrestore(&hbus->device_list_lock, flags);

        if (!dr) {
                up(&hbus->enum_sem);
                put_hvpcibus(hbus);
                return;
        }

        /* First, mark all existing children as reported missing. */
        spin_lock_irqsave(&hbus->device_list_lock, flags);
        list_for_each(iter, &hbus->children) {
                        hpdev = container_of(iter, struct hv_pci_dev,
                                             list_entry);
                        hpdev->reported_missing = true;
        }
        spin_unlock_irqrestore(&hbus->device_list_lock, flags);

        /* Next, add back any reported devices. */
        for (child_no = 0; child_no < dr->device_count; child_no++) {
                found = false;
                new_desc = &dr->func[child_no];

                spin_lock_irqsave(&hbus->device_list_lock, flags);
                list_for_each(iter, &hbus->children) {
                        hpdev = container_of(iter, struct hv_pci_dev,
                                             list_entry);
                        if ((hpdev->desc.win_slot.slot ==
                             new_desc->win_slot.slot) &&
                            (hpdev->desc.v_id == new_desc->v_id) &&
                            (hpdev->desc.d_id == new_desc->d_id) &&
                            (hpdev->desc.ser == new_desc->ser)) {
                                hpdev->reported_missing = false;
                                found = true;
                        }
                }
                spin_unlock_irqrestore(&hbus->device_list_lock, flags);

                if (!found) {
                        hpdev = new_pcichild_device(hbus, new_desc);
                        if (!hpdev)
                                dev_err(&hbus->hdev->device,
                                        "couldn't record a child device.\n");
                }
        }

        /* Move missing children to a list on the stack. */
        spin_lock_irqsave(&hbus->device_list_lock, flags);
        do {
                found = false;
                list_for_each(iter, &hbus->children) {
                        hpdev = container_of(iter, struct hv_pci_dev,
                                             list_entry);
                        if (hpdev->reported_missing) {
                                found = true;
                                put_pcichild(hpdev, hv_pcidev_ref_childlist);
                                list_move_tail(&hpdev->list_entry, &removed);
                                break;
                        }
                }
        } while (found);
        spin_unlock_irqrestore(&hbus->device_list_lock, flags);

        /* Delete everything that should no longer exist. */
        while (!list_empty(&removed)) {
                hpdev = list_first_entry(&removed, struct hv_pci_dev,
                                         list_entry);
                list_del(&hpdev->list_entry);
                put_pcichild(hpdev, hv_pcidev_ref_initial);
        }

        /* Tell the core to rescan bus because there may have been changes. */
        if (hbus->state == hv_pcibus_installed) {
                pci_lock_rescan_remove();
                pci_scan_child_bus(hbus->pci_bus);
                pci_unlock_rescan_remove();
        } else {
                survey_child_resources(hbus);
        }

        up(&hbus->enum_sem);
        put_hvpcibus(hbus);
        kfree(dr);
}

/**
 * hv_pci_devices_present() - Handles list of new children
 * @hbus:       Root PCI bus, as understood by this driver
 * @relations:  Packet from host listing children
 *
 * This function is invoked whenever a new list of devices for
 * this bus appears.
 */
static void hv_pci_devices_present(struct hv_pcibus_device *hbus,
                                   struct pci_bus_relations *relations)
{
        struct hv_dr_state *dr;
        struct hv_dr_work *dr_wrk;
        unsigned long flags;

        dr_wrk = kzalloc(sizeof(*dr_wrk), GFP_NOWAIT);
        if (!dr_wrk)
                return;

        dr = kzalloc(offsetof(struct hv_dr_state, func) +
                     (sizeof(struct pci_function_description) *
                      (relations->device_count)), GFP_NOWAIT);
        if (!dr)  {
                kfree(dr_wrk);
                return;
        }

        INIT_WORK(&dr_wrk->wrk, pci_devices_present_work);
        dr_wrk->bus = hbus;
        dr->device_count = relations->device_count;
        if (dr->device_count != 0) {
                memcpy(dr->func, relations->func,
                       sizeof(struct pci_function_description) *
                       dr->device_count);
        }

        spin_lock_irqsave(&hbus->device_list_lock, flags);
        list_add_tail(&dr->list_entry, &hbus->dr_list);
        spin_unlock_irqrestore(&hbus->device_list_lock, flags);

        get_hvpcibus(hbus);
        schedule_work(&dr_wrk->wrk);
}

/**
 * hv_eject_device_work() - Asynchronously handles ejection
 * @work:       Work struct embedded in internal device struct
 *
 * This function handles ejecting a device.  Windows will
 * attempt to gracefully eject a device, waiting 60 seconds to
 * hear back from the guest OS that this completed successfully.
 * If this timer expires, the device will be forcibly removed.
 */
static void hv_eject_device_work(struct work_struct *work)
{
        struct pci_eject_response *ejct_pkt;
        struct hv_pci_dev *hpdev;
        struct pci_dev *pdev;
        unsigned long flags;
        int wslot;
        struct {
                struct pci_packet pkt;
                u8 buffer[sizeof(struct pci_eject_response)];
        } ctxt;

        hpdev = container_of(work, struct hv_pci_dev, wrk);

        if (hpdev->state != hv_pcichild_ejecting) {
                put_pcichild(hpdev, hv_pcidev_ref_pnp);
                return;
        }

        /*
         * Ejection can come before or after the PCI bus has been set up, so
         * attempt to find it and tear down the bus state, if it exists.  This
         * must be done without constructs like pci_domain_nr(hbus->pci_bus)
         * because hbus->pci_bus may not exist yet.
         */
        wslot = wslot_to_devfn(hpdev->desc.win_slot.slot);
        pdev = pci_get_domain_bus_and_slot(hpdev->hbus->sysdata.domain, 0,
                                           wslot);
        if (pdev) {
                pci_stop_and_remove_bus_device(pdev);
                pci_dev_put(pdev);
        }

        spin_lock_irqsave(&hpdev->hbus->device_list_lock, flags);
        list_del(&hpdev->list_entry);
        spin_unlock_irqrestore(&hpdev->hbus->device_list_lock, flags);

        memset(&ctxt, 0, sizeof(ctxt));
        ejct_pkt = (struct pci_eject_response *)&ctxt.pkt.message;
        ejct_pkt->message_type.type = PCI_EJECTION_COMPLETE;
        ejct_pkt->wslot.slot = hpdev->desc.win_slot.slot;
        vmbus_sendpacket(hpdev->hbus->hdev->channel, ejct_pkt,
                         sizeof(*ejct_pkt), (unsigned long)&ctxt.pkt,
                         VM_PKT_DATA_INBAND, 0);

        put_pcichild(hpdev, hv_pcidev_ref_childlist);
        put_pcichild(hpdev, hv_pcidev_ref_pnp);
        put_hvpcibus(hpdev->hbus);
}

/**
 * hv_pci_eject_device() - Handles device ejection
 * @hpdev:      Internal device tracking struct
 *
 * This function is invoked when an ejection packet arrives.  It
 * just schedules work so that we don't re-enter the packet
 * delivery code handling the ejection.
 */
static void hv_pci_eject_device(struct hv_pci_dev *hpdev)
{
        hpdev->state = hv_pcichild_ejecting;
        get_pcichild(hpdev, hv_pcidev_ref_pnp);
        INIT_WORK(&hpdev->wrk, hv_eject_device_work);
        get_hvpcibus(hpdev->hbus);
        schedule_work(&hpdev->wrk);
}

/**
 * hv_pci_onchannelcallback() - Handles incoming packets
 * @context:    Internal bus tracking struct
 *
 * This function is invoked whenever the host sends a packet to
 * this channel (which is private to this root PCI bus).
 */
static void hv_pci_onchannelcallback(void *context)
{
        const int packet_size = 0x100;
        int ret;
        struct hv_pcibus_device *hbus = context;
        u32 bytes_recvd;
        u64 req_id;
        struct vmpacket_descriptor *desc;
        unsigned char *buffer;
        int bufferlen = packet_size;
        struct pci_packet *comp_packet;
        struct pci_response *response;
        struct pci_incoming_message *new_message;
        struct pci_bus_relations *bus_rel;
        struct pci_dev_incoming *dev_message;
        struct hv_pci_dev *hpdev;

        buffer = kmalloc(bufferlen, GFP_ATOMIC);
        if (!buffer)
                return;

        while (1) {
                ret = vmbus_recvpacket_raw(hbus->hdev->channel, buffer,
                                           bufferlen, &bytes_recvd, &req_id);

                if (ret == -ENOBUFS) {
                        kfree(buffer);
                        /* Handle large packet */
                        bufferlen = bytes_recvd;
                        buffer = kmalloc(bytes_recvd, GFP_ATOMIC);
                        if (!buffer)
                                return;
                        continue;
                }

                /* Zero length indicates there are no more packets. */
                if (ret || !bytes_recvd)
                        break;

                /*
                 * All incoming packets must be at least as large as a
                 * response.
                 */
                if (bytes_recvd <= sizeof(struct pci_response))
                        continue;
                desc = (struct vmpacket_descriptor *)buffer;

                switch (desc->type) {
                case VM_PKT_COMP:

                        /*
                         * The host is trusted, and thus it's safe to interpret
                         * this transaction ID as a pointer.
                         */
                        comp_packet = (struct pci_packet *)req_id;
                        response = (struct pci_response *)buffer;
                        comp_packet->completion_func(comp_packet->compl_ctxt,
                                                     response,
                                                     bytes_recvd);
                        break;

                case VM_PKT_DATA_INBAND:

                        new_message = (struct pci_incoming_message *)buffer;
                        switch (new_message->message_type.type) {
                        case PCI_BUS_RELATIONS:

                                bus_rel = (struct pci_bus_relations *)buffer;
                                if (bytes_recvd <
                                    offsetof(struct pci_bus_relations, func) +
                                    (sizeof(struct pci_function_description) *
                                     (bus_rel->device_count))) {
                                        dev_err(&hbus->hdev->device,
                                                "bus relations too small\n");
                                        break;
                                }

                                hv_pci_devices_present(hbus, bus_rel);
                                break;

                        case PCI_EJECT:

                                dev_message = (struct pci_dev_incoming *)buffer;
                                hpdev = get_pcichild_wslot(hbus,
                                                      dev_message->wslot.slot);
                                if (hpdev) {
                                        hv_pci_eject_device(hpdev);
                                        put_pcichild(hpdev,
                                                        hv_pcidev_ref_by_slot);
                                }
                                break;

                        default:
                                dev_warn(&hbus->hdev->device,
                                        "Unimplemented protocol message %x\n",
                                        new_message->message_type.type);
                                break;
                        }
                        break;

                default:
                        dev_err(&hbus->hdev->device,
                                "unhandled packet type %d, tid %llx len %d\n",
                                desc->type, req_id, bytes_recvd);
                        break;
                }
        }

        kfree(buffer);
}

/**
 * hv_pci_protocol_negotiation() - Set up protocol
 * @hdev:       VMBus's tracking struct for this root PCI bus
 *
 * This driver is intended to support running on Windows 10
 * (server) and later versions. It will not run on earlier
 * versions, as they assume that many of the operations which
 * Linux needs accomplished with a spinlock held were done via
 * asynchronous messaging via VMBus.  Windows 10 increases the
 * surface area of PCI emulation so that these actions can take
 * place by suspending a virtual processor for their duration.
 *
 * This function negotiates the channel protocol version,
 * failing if the host doesn't support the necessary protocol
 * level.
 */
static int hv_pci_protocol_negotiation(struct hv_device *hdev)
{
        struct pci_version_request *version_req;
        struct hv_pci_compl comp_pkt;
        struct pci_packet *pkt;
        int ret;

        /*
         * Initiate the handshake with the host and negotiate
         * a version that the host can support. We start with the
         * highest version number and go down if the host cannot
         * support it.
         */
        pkt = kzalloc(sizeof(*pkt) + sizeof(*version_req), GFP_KERNEL);
        if (!pkt)
                return -ENOMEM;

        init_completion(&comp_pkt.host_event);
        pkt->completion_func = hv_pci_generic_compl;
        pkt->compl_ctxt = &comp_pkt;
        version_req = (struct pci_version_request *)&pkt->message;
        version_req->message_type.type = PCI_QUERY_PROTOCOL_VERSION;
        version_req->protocol_version = PCI_PROTOCOL_VERSION_CURRENT;

        ret = vmbus_sendpacket(hdev->channel, version_req,
                               sizeof(struct pci_version_request),
                               (unsigned long)pkt, VM_PKT_DATA_INBAND,
                               VMBUS_DATA_PACKET_FLAG_COMPLETION_REQUESTED);
        if (ret)
                goto exit;

        wait_for_completion(&comp_pkt.host_event);

        if (comp_pkt.completion_status < 0) {
                dev_err(&hdev->device,
                        "PCI Pass-through VSP failed version request %x\n",
                        comp_pkt.completion_status);
                ret = -EPROTO;
                goto exit;
        }

        ret = 0;

exit:
        kfree(pkt);
        return ret;
}

/**
 * hv_pci_free_bridge_windows() - Release memory regions for the
 * bus
 * @hbus:       Root PCI bus, as understood by this driver
 */
static void hv_pci_free_bridge_windows(struct hv_pcibus_device *hbus)
{
        /*
         * Set the resources back to the way they looked when they
         * were allocated by setting IORESOURCE_BUSY again.
         */

        if (hbus->low_mmio_space && hbus->low_mmio_res) {
                hbus->low_mmio_res->flags |= IORESOURCE_BUSY;
                vmbus_free_mmio(hbus->low_mmio_res->start,
                                resource_size(hbus->low_mmio_res));
        }

        if (hbus->high_mmio_space && hbus->high_mmio_res) {
                hbus->high_mmio_res->flags |= IORESOURCE_BUSY;
                vmbus_free_mmio(hbus->high_mmio_res->start,
                                resource_size(hbus->high_mmio_res));
        }
}

/**
 * hv_pci_allocate_bridge_windows() - Allocate memory regions
 * for the bus
 * @hbus:       Root PCI bus, as understood by this driver
 *
 * This function calls vmbus_allocate_mmio(), which is itself a
 * bit of a compromise.  Ideally, we might change the pnp layer
 * in the kernel such that it comprehends either PCI devices
 * which are "grandchildren of ACPI," with some intermediate bus
 * node (in this case, VMBus) or change it such that it
 * understands VMBus.  The pnp layer, however, has been declared
 * deprecated, and not subject to change.
 *
 * The workaround, implemented here, is to ask VMBus to allocate
 * MMIO space for this bus.  VMBus itself knows which ranges are
 * appropriate by looking at its own ACPI objects.  Then, after
 * these ranges are claimed, they're modified to look like they
 * would have looked if the ACPI and pnp code had allocated
 * bridge windows.  These descriptors have to exist in this form
 * in order to satisfy the code which will get invoked when the
 * endpoint PCI function driver calls request_mem_region() or
 * request_mem_region_exclusive().
 *
 * Return: 0 on success, -errno on failure
 */
static int hv_pci_allocate_bridge_windows(struct hv_pcibus_device *hbus)
{
        resource_size_t align;
        int ret;

        if (hbus->low_mmio_space) {
                align = 1ULL << (63 - __builtin_clzll(hbus->low_mmio_space));
                ret = vmbus_allocate_mmio(&hbus->low_mmio_res, hbus->hdev, 0,
                                          (u64)(u32)0xffffffff,
                                          hbus->low_mmio_space,
                                          align, false);
                if (ret) {
                        dev_err(&hbus->hdev->device,
                                "Need %#llx of low MMIO space. Consider reconfiguring the VM.\n",
                                hbus->low_mmio_space);
                        return ret;
                }

                /* Modify this resource to become a bridge window. */
                hbus->low_mmio_res->flags |= IORESOURCE_WINDOW;
                hbus->low_mmio_res->flags &= ~IORESOURCE_BUSY;
                pci_add_resource(&hbus->resources_for_children,
                                 hbus->low_mmio_res);
        }

        if (hbus->high_mmio_space) {
                align = 1ULL << (63 - __builtin_clzll(hbus->high_mmio_space));
                ret = vmbus_allocate_mmio(&hbus->high_mmio_res, hbus->hdev,
                                          0x100000000, -1,
                                          hbus->high_mmio_space, align,
                                          false);
                if (ret) {
                        dev_err(&hbus->hdev->device,
                                "Need %#llx of high MMIO space. Consider reconfiguring the VM.\n",
                                hbus->high_mmio_space);
                        goto release_low_mmio;
                }

                /* Modify this resource to become a bridge window. */
                hbus->high_mmio_res->flags |= IORESOURCE_WINDOW;
                hbus->high_mmio_res->flags &= ~IORESOURCE_BUSY;
                pci_add_resource(&hbus->resources_for_children,
                                 hbus->high_mmio_res);
        }

        return 0;

release_low_mmio:
        if (hbus->low_mmio_res) {
                vmbus_free_mmio(hbus->low_mmio_res->start,
                                resource_size(hbus->low_mmio_res));
        }

        return ret;
}

/**
 * hv_allocate_config_window() - Find MMIO space for PCI Config
 * @hbus:       Root PCI bus, as understood by this driver
 *
 * This function claims memory-mapped I/O space for accessing
 * configuration space for the functions on this bus.
 *
 * Return: 0 on success, -errno on failure
 */
static int hv_allocate_config_window(struct hv_pcibus_device *hbus)
{
        int ret;

        /*
         * Set up a region of MMIO space to use for accessing configuration
         * space.
         */
        ret = vmbus_allocate_mmio(&hbus->mem_config, hbus->hdev, 0, -1,
                                  PCI_CONFIG_MMIO_LENGTH, 0x1000, false);
        if (ret)
                return ret;

        /*
         * vmbus_allocate_mmio() gets used for allocating both device endpoint
         * resource claims (those which cannot be overlapped) and the ranges
         * which are valid for the children of this bus, which are intended
         * to be overlapped by those children.  Set the flag on this claim
         * meaning that this region can't be overlapped.
         */

        hbus->mem_config->flags |= IORESOURCE_BUSY;

        return 0;
}

static void hv_free_config_window(struct hv_pcibus_device *hbus)
{
        vmbus_free_mmio(hbus->mem_config->start, PCI_CONFIG_MMIO_LENGTH);
}

/**
 * hv_pci_enter_d0() - Bring the "bus" into the D0 power state
 * @hdev:       VMBus's tracking struct for this root PCI bus
 *
 * Return: 0 on success, -errno on failure
 */
static int hv_pci_enter_d0(struct hv_device *hdev)
{
        struct hv_pcibus_device *hbus = hv_get_drvdata(hdev);
        struct pci_bus_d0_entry *d0_entry;
        struct hv_pci_compl comp_pkt;
        struct pci_packet *pkt;
        int ret;

        /*
         * Tell the host that the bus is ready to use, and moved into the
         * powered-on state.  This includes telling the host which region
         * of memory-mapped I/O space has been chosen for configuration space
         * access.
         */
        pkt = kzalloc(sizeof(*pkt) + sizeof(*d0_entry), GFP_KERNEL);
        if (!pkt)
                return -ENOMEM;

        init_completion(&comp_pkt.host_event);
        pkt->completion_func = hv_pci_generic_compl;
        pkt->compl_ctxt = &comp_pkt;
        d0_entry = (struct pci_bus_d0_entry *)&pkt->message;
        d0_entry->message_type.type = PCI_BUS_D0ENTRY;
        d0_entry->mmio_base = hbus->mem_config->start;

        ret = vmbus_sendpacket(hdev->channel, d0_entry, sizeof(*d0_entry),
                               (unsigned long)pkt, VM_PKT_DATA_INBAND,
                               VMBUS_DATA_PACKET_FLAG_COMPLETION_REQUESTED);
        if (ret)
                goto exit;

        wait_for_completion(&comp_pkt.host_event);

        if (comp_pkt.completion_status < 0) {
                dev_err(&hdev->device,
                        "PCI Pass-through VSP failed D0 Entry with status %x\n",
                        comp_pkt.completion_status);
                ret = -EPROTO;
                goto exit;
        }

        ret = 0;

exit:
        kfree(pkt);
        return ret;
}

/**
 * hv_pci_query_relations() - Ask host to send list of child
 * devices
 * @hdev:       VMBus's tracking struct for this root PCI bus
 *
 * Return: 0 on success, -errno on failure
 */
static int hv_pci_query_relations(struct hv_device *hdev)
{
        struct hv_pcibus_device *hbus = hv_get_drvdata(hdev);
        struct pci_message message;
        struct completion comp;
        int ret;

        /* Ask the host to send along the list of child devices */
        init_completion(&comp);
        if (cmpxchg(&hbus->survey_event, NULL, &comp))
                return -ENOTEMPTY;

        memset(&message, 0, sizeof(message));
        message.type = PCI_QUERY_BUS_RELATIONS;

        ret = vmbus_sendpacket(hdev->channel, &message, sizeof(message),
                               0, VM_PKT_DATA_INBAND, 0);
        if (ret)
                return ret;

        wait_for_completion(&comp);
        return 0;
}

/**
 * hv_send_resources_allocated() - Report local resource choices
 * @hdev:       VMBus's tracking struct for this root PCI bus
 *
 * The host OS is expecting to be sent a request as a message
 * which contains all the resources that the device will use.
 * The response contains those same resources, "translated"
 * which is to say, the values which should be used by the
 * hardware, when it delivers an interrupt.  (MMIO resources are
 * used in local terms.)  This is nice for Windows, and lines up
 * with the FDO/PDO split, which doesn't exist in Linux.  Linux
 * is deeply expecting to scan an emulated PCI configuration
 * space.  So this message is sent here only to drive the state
 * machine on the host forward.
 *
 * Return: 0 on success, -errno on failure
 */
static int hv_send_resources_allocated(struct hv_device *hdev)
{
        struct hv_pcibus_device *hbus = hv_get_drvdata(hdev);
        struct pci_resources_assigned *res_assigned;
        struct hv_pci_compl comp_pkt;
        struct hv_pci_dev *hpdev;
        struct pci_packet *pkt;
        u32 wslot;
        int ret;

        pkt = kmalloc(sizeof(*pkt) + sizeof(*res_assigned), GFP_KERNEL);
        if (!pkt)
                return -ENOMEM;

        ret = 0;

        for (wslot = 0; wslot < 256; wslot++) {
                hpdev = get_pcichild_wslot(hbus, wslot);
                if (!hpdev)
                        continue;

                memset(pkt, 0, sizeof(*pkt) + sizeof(*res_assigned));
                init_completion(&comp_pkt.host_event);
                pkt->completion_func = hv_pci_generic_compl;
                pkt->compl_ctxt = &comp_pkt;
                res_assigned = (struct pci_resources_assigned *)&pkt->message;
                res_assigned->message_type.type = PCI_RESOURCES_ASSIGNED;
                res_assigned->wslot.slot = hpdev->desc.win_slot.slot;

                put_pcichild(hpdev, hv_pcidev_ref_by_slot);

                ret = vmbus_sendpacket(
                        hdev->channel, &pkt->message,
                        sizeof(*res_assigned),
                        (unsigned long)pkt,
                        VM_PKT_DATA_INBAND,
                        VMBUS_DATA_PACKET_FLAG_COMPLETION_REQUESTED);
                if (ret)
                        break;

                wait_for_completion(&comp_pkt.host_event);

                if (comp_pkt.completion_status < 0) {
                        ret = -EPROTO;
                        dev_err(&hdev->device,
                                "resource allocated returned 0x%x",
                                comp_pkt.completion_status);
                        break;
                }
        }

        kfree(pkt);
        return ret;
}

/**
 * hv_send_resources_released() - Report local resources
 * released
 * @hdev:       VMBus's tracking struct for this root PCI bus
 *
 * Return: 0 on success, -errno on failure
 */
static int hv_send_resources_released(struct hv_device *hdev)
{
        struct hv_pcibus_device *hbus = hv_get_drvdata(hdev);
        struct pci_child_message pkt;
        struct hv_pci_dev *hpdev;
        u32 wslot;
        int ret;

        for (wslot = 0; wslot < 256; wslot++) {
                hpdev = get_pcichild_wslot(hbus, wslot);
                if (!hpdev)
                        continue;

                memset(&pkt, 0, sizeof(pkt));
                pkt.message_type.type = PCI_RESOURCES_RELEASED;
                pkt.wslot.slot = hpdev->desc.win_slot.slot;

                put_pcichild(hpdev, hv_pcidev_ref_by_slot);

                ret = vmbus_sendpacket(hdev->channel, &pkt, sizeof(pkt), 0,
                                       VM_PKT_DATA_INBAND, 0);
                if (ret)
                        return ret;
        }

        return 0;
}

static void get_hvpcibus(struct hv_pcibus_device *hbus)
{
        atomic_inc(&hbus->remove_lock);
}

static void put_hvpcibus(struct hv_pcibus_device *hbus)
{
        if (atomic_dec_and_test(&hbus->remove_lock))
                complete(&hbus->remove_event);
}

/**
 * hv_pci_probe() - New VMBus channel probe, for a root PCI bus
 * @hdev:       VMBus's tracking struct for this root PCI bus
 * @dev_id:     Identifies the device itself
 *
 * Return: 0 on success, -errno on failure
 */
static int hv_pci_probe(struct hv_device *hdev,
                        const struct hv_vmbus_device_id *dev_id)
{
        struct hv_pcibus_device *hbus;
        int ret;

        hbus = kzalloc(sizeof(*hbus), GFP_KERNEL);
        if (!hbus)
                return -ENOMEM;

        /*
         * The PCI bus "domain" is what is called "segment" in ACPI and
         * other specs.  Pull it from the instance ID, to get something
         * unique.  Bytes 8 and 9 are what is used in Windows guests, so
         * do the same thing for consistency.  Note that, since this code
         * only runs in a Hyper-V VM, Hyper-V can (and does) guarantee
         * that (1) the only domain in use for something that looks like
         * a physical PCI bus (which is actually emulated by the
         * hypervisor) is domain 0 and (2) there will be no overlap
         * between domains derived from these instance IDs in the same
         * VM.
         */
        hbus->sysdata.domain = hdev->dev_instance.b[9] |
                               hdev->dev_instance.b[8] << 8;

        hbus->hdev = hdev;
        atomic_inc(&hbus->remove_lock);
        INIT_LIST_HEAD(&hbus->children);
        INIT_LIST_HEAD(&hbus->dr_list);
        INIT_LIST_HEAD(&hbus->resources_for_children);
        spin_lock_init(&hbus->config_lock);
        spin_lock_init(&hbus->device_list_lock);
        spin_lock_init(&hbus->retarget_msi_interrupt_lock);
        sema_init(&hbus->enum_sem, 1);
        init_completion(&hbus->remove_event);

        ret = vmbus_open(hdev->channel, pci_ring_size, pci_ring_size, NULL, 0,
                         hv_pci_onchannelcallback, hbus);
        if (ret)
                goto free_bus;

        hv_set_drvdata(hdev, hbus);

        ret = hv_pci_protocol_negotiation(hdev);
        if (ret)
                goto close;

        ret = hv_allocate_config_window(hbus);
        if (ret)
                goto close;

        hbus->cfg_addr = ioremap(hbus->mem_config->start,
                                 PCI_CONFIG_MMIO_LENGTH);
        if (!hbus->cfg_addr) {
                dev_err(&hdev->device,
                        "Unable to map a virtual address for config space\n");
                ret = -ENOMEM;
                goto free_config;
        }

        hbus->sysdata.fwnode = irq_domain_alloc_fwnode(hbus);
        if (!hbus->sysdata.fwnode) {
                ret = -ENOMEM;
                goto unmap;
        }

        ret = hv_pcie_init_irq_domain(hbus);
        if (ret)
                goto free_fwnode;

        ret = hv_pci_query_relations(hdev);
        if (ret)
                goto free_irq_domain;

        ret = hv_pci_enter_d0(hdev);
        if (ret)
                goto free_irq_domain;

        ret = hv_pci_allocate_bridge_windows(hbus);
        if (ret)
                goto free_irq_domain;

        ret = hv_send_resources_allocated(hdev);
        if (ret)
                goto free_windows;

        prepopulate_bars(hbus);

        hbus->state = hv_pcibus_probed;

        ret = create_root_hv_pci_bus(hbus);
        if (ret)
                goto free_windows;

        return 0;

free_windows:
        hv_pci_free_bridge_windows(hbus);
free_irq_domain:
        irq_domain_remove(hbus->irq_domain);
free_fwnode:
        irq_domain_free_fwnode(hbus->sysdata.fwnode);
unmap:
        iounmap(hbus->cfg_addr);
free_config:
        hv_free_config_window(hbus);
close:
        vmbus_close(hdev->channel);
free_bus:
        kfree(hbus);
        return ret;
}

static void hv_pci_bus_exit(struct hv_device *hdev)
{
        struct hv_pcibus_device *hbus = hv_get_drvdata(hdev);
        struct {
                struct pci_packet teardown_packet;
                u8 buffer[sizeof(struct pci_message)];
        } pkt;
        struct pci_bus_relations relations;
        struct hv_pci_compl comp_pkt;
        int ret;

        /*
         * After the host sends the RESCIND_CHANNEL message, it doesn't
         * access the per-channel ringbuffer any longer.
         */
        if (hdev->channel->rescind)
                return;

        /* Delete any children which might still exist. */
        memset(&relations, 0, sizeof(relations));
        hv_pci_devices_present(hbus, &relations);

        ret = hv_send_resources_released(hdev);
        if (ret)
                dev_err(&hdev->device,
                        "Couldn't send resources released packet(s)\n");

        memset(&pkt.teardown_packet, 0, sizeof(pkt.teardown_packet));
        init_completion(&comp_pkt.host_event);
        pkt.teardown_packet.completion_func = hv_pci_generic_compl;
        pkt.teardown_packet.compl_ctxt = &comp_pkt;
        pkt.teardown_packet.message[0].type = PCI_BUS_D0EXIT;

        ret = vmbus_sendpacket(hdev->channel, &pkt.teardown_packet.message,
                               sizeof(struct pci_message),
                               (unsigned long)&pkt.teardown_packet,
                               VM_PKT_DATA_INBAND,
                               VMBUS_DATA_PACKET_FLAG_COMPLETION_REQUESTED);
        if (!ret)
                wait_for_completion_timeout(&comp_pkt.host_event, 10 * HZ);
}

/**
 * hv_pci_remove() - Remove routine for this VMBus channel
 * @hdev:       VMBus's tracking struct for this root PCI bus
 *
 * Return: 0 on success, -errno on failure
 */
static int hv_pci_remove(struct hv_device *hdev)
{
        struct hv_pcibus_device *hbus;

        hbus = hv_get_drvdata(hdev);
        if (hbus->state == hv_pcibus_installed) {
                /* Remove the bus from PCI's point of view. */
                pci_lock_rescan_remove();
                pci_stop_root_bus(hbus->pci_bus);
                pci_remove_root_bus(hbus->pci_bus);
                pci_unlock_rescan_remove();
        }

        hv_pci_bus_exit(hdev);

        vmbus_close(hdev->channel);

        iounmap(hbus->cfg_addr);
        hv_free_config_window(hbus);
        pci_free_resource_list(&hbus->resources_for_children);
        hv_pci_free_bridge_windows(hbus);
        irq_domain_remove(hbus->irq_domain);
        irq_domain_free_fwnode(hbus->sysdata.fwnode);
        put_hvpcibus(hbus);
        wait_for_completion(&hbus->remove_event);
        kfree(hbus);
        return 0;
}

static const struct hv_vmbus_device_id hv_pci_id_table[] = {
        /* PCI Pass-through Class ID */
        /* 44C4F61D-4444-4400-9D52-802E27EDE19F */
        { HV_PCIE_GUID, },
        { },
};

MODULE_DEVICE_TABLE(vmbus, hv_pci_id_table);

static struct hv_driver hv_pci_drv = {
        .name           = "hv_pci",
        .id_table       = hv_pci_id_table,
        .probe          = hv_pci_probe,
        .remove         = hv_pci_remove,
};

static void __exit exit_hv_pci_drv(void)
{
        vmbus_driver_unregister(&hv_pci_drv);
}

static int __init init_hv_pci_drv(void)
{
        return vmbus_driver_register(&hv_pci_drv);
}

module_init(init_hv_pci_drv);
module_exit(exit_hv_pci_drv);

MODULE_DESCRIPTION("Hyper-V PCI");
MODULE_LICENSE("GPL v2");