x86/apic: Initialize Secure AVIC APIC backing page

With Secure AVIC, the APIC backing page is owned and managed by the guest.
Allocate and initialize APIC backing page for all guest CPUs.

The NPT entry for a vCPU's APIC backing page must always be present when the
vCPU is running in order for Secure AVIC to function. A VMEXIT_BUSY is
returned on VMRUN and the vCPU cannot be resumed otherwise.

To handle this, notify GPA of the vCPU's APIC backing page to the hypervisor
by using the SVM_VMGEXIT_SECURE_AVIC GHCB protocol event. Before executing
VMRUN, the hypervisor makes use of this information to make sure the APIC
backing page is mapped in the NPT.

  [ bp: Massage commit message. ]

Co-developed-by: Kishon Vijay Abraham I <kvijayab@amd.com>
Signed-off-by: Kishon Vijay Abraham I <kvijayab@amd.com>
Signed-off-by: Neeraj Upadhyay <Neeraj.Upadhyay@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Tianyu Lan <tiala@microsoft.com>
Link: https://lore.kernel.org/20250828070334.208401-3-Neeraj.Upadhyay@amd.com

diff --git a/arch/x86/coco/sev/core.c b/arch/x86/coco/sev/core.c
index f7a549f650e9c4e7dd1a384069eb333e857ede7b..7669aafcad95be5563767bcfc8a8a3593dbc3640 100644 (file)
--- a/arch/x86/coco/sev/core.c
+++ b/arch/x86/coco/sev/core.c
@@ -1108,6 +1108,28 @@ int __init sev_es_efi_map_ghcbs_cas(pgd_t *pgd)
        return 0;
 }
 
+enum es_result savic_register_gpa(u64 gpa)
+{
+       struct ghcb_state state;
+       struct es_em_ctxt ctxt;
+       enum es_result res;
+       struct ghcb *ghcb;
+
+       guard(irqsave)();
+
+       ghcb = __sev_get_ghcb(&state);
+       vc_ghcb_invalidate(ghcb);
+
+       ghcb_set_rax(ghcb, SVM_VMGEXIT_SAVIC_SELF_GPA);
+       ghcb_set_rbx(ghcb, gpa);
+       res = sev_es_ghcb_hv_call(ghcb, &ctxt, SVM_VMGEXIT_SAVIC,
+                                 SVM_VMGEXIT_SAVIC_REGISTER_GPA, 0);
+
+       __sev_put_ghcb(&state);
+
+       return res;
+}
+
 static void snp_register_per_cpu_ghcb(void)
 {
        struct sev_es_runtime_data *data;

diff --git a/arch/x86/include/asm/apic.h b/arch/x86/include/asm/apic.h
index 07ba4935e8732009a16a7026104dc425c0ccde0f..44b4080721a62548a4a8249f9658acb6e730327c 100644 (file)
--- a/arch/x86/include/asm/apic.h
+++ b/arch/x86/include/asm/apic.h
@@ -305,6 +305,7 @@ struct apic {
 
        /* Probe, setup and smpboot functions */
        int     (*probe)(void);
+       void    (*setup)(void);
        int     (*acpi_madt_oem_check)(char *oem_id, char *oem_table_id);
 
        void    (*init_apic_ldr)(void);

diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
index 02236962fdb108009e419e010d3862688e1f694d..9036122a6d455d97ad09545821ee55e613e60176 100644 (file)
--- a/arch/x86/include/asm/sev.h
+++ b/arch/x86/include/asm/sev.h
@@ -533,6 +533,7 @@ int snp_svsm_vtpm_send_command(u8 *buffer);
 
 void __init snp_secure_tsc_prepare(void);
 void __init snp_secure_tsc_init(void);
+enum es_result savic_register_gpa(u64 gpa);
 
 static __always_inline void vc_ghcb_invalidate(struct ghcb *ghcb)
 {
@@ -605,6 +606,7 @@ static inline int snp_send_guest_request(struct snp_msg_desc *mdesc,
 static inline int snp_svsm_vtpm_send_command(u8 *buffer) { return -ENODEV; }
 static inline void __init snp_secure_tsc_prepare(void) { }
 static inline void __init snp_secure_tsc_init(void) { }
+static inline enum es_result savic_register_gpa(u64 gpa) { return ES_UNSUPPORTED; }
 
 #endif /* CONFIG_AMD_MEM_ENCRYPT */
 

diff --git a/arch/x86/include/uapi/asm/svm.h b/arch/x86/include/uapi/asm/svm.h
index 9c640a521a67006da1e59df64e167808e9794252..650e3256ea7d7339091b86adfbd317ac5d25d61a 100644 (file)
--- a/arch/x86/include/uapi/asm/svm.h
+++ b/arch/x86/include/uapi/asm/svm.h
@@ -118,6 +118,10 @@
 #define SVM_VMGEXIT_AP_CREATE                  1
 #define SVM_VMGEXIT_AP_DESTROY                 2
 #define SVM_VMGEXIT_SNP_RUN_VMPL               0x80000018
+#define SVM_VMGEXIT_SAVIC                      0x8000001a
+#define SVM_VMGEXIT_SAVIC_REGISTER_GPA         0
+#define SVM_VMGEXIT_SAVIC_UNREGISTER_GPA       1
+#define SVM_VMGEXIT_SAVIC_SELF_GPA             ~0ULL
 #define SVM_VMGEXIT_HV_FEATURES                        0x8000fffd
 #define SVM_VMGEXIT_TERM_REQUEST               0x8000fffe
 #define SVM_VMGEXIT_TERM_REASON(reason_set, reason_code)       \

diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index ff4029b57e95676f1ad444d88943d88c495fe551..7874284c1ca7fdcafdaee1501efcf6caac1bcc8e 100644 (file)
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -1501,6 +1501,9 @@ static void setup_local_APIC(void)
                return;
        }
 
+       if (apic->setup)
+               apic->setup();
+
        /*
         * If this comes from kexec/kcrash the APIC might be enabled in
         * SPIV. Soft disable it before doing further initialization.

diff --git a/arch/x86/kernel/apic/x2apic_savic.c b/arch/x86/kernel/apic/x2apic_savic.c
index bea844f28192c1fc9aa7aa639ec7531cf44871bd..948d89497baafdd026b9171c986ec894c3aefccf 100644 (file)
--- a/arch/x86/kernel/apic/x2apic_savic.c
+++ b/arch/x86/kernel/apic/x2apic_savic.c
@@ -8,17 +8,47 @@
  */
 
 #include <linux/cc_platform.h>
+#include <linux/percpu-defs.h>
 
 #include <asm/apic.h>
 #include <asm/sev.h>
 
 #include "local.h"
 
+struct secure_avic_page {
+       u8 regs[PAGE_SIZE];
+} __aligned(PAGE_SIZE);
+
+static struct secure_avic_page __percpu *savic_page __ro_after_init;
+
 static int savic_acpi_madt_oem_check(char *oem_id, char *oem_table_id)
 {
        return x2apic_enabled() && cc_platform_has(CC_ATTR_SNP_SECURE_AVIC);
 }
 
+static void savic_setup(void)
+{
+       void *ap = this_cpu_ptr(savic_page);
+       enum es_result res;
+       unsigned long gpa;
+
+       gpa = __pa(ap);
+
+       /*
+        * The NPT entry for a vCPU's APIC backing page must always be
+        * present when the vCPU is running in order for Secure AVIC to
+        * function. A VMEXIT_BUSY is returned on VMRUN and the vCPU cannot
+        * be resumed if the NPT entry for the APIC backing page is not
+        * present. Notify GPA of the vCPU's APIC backing page to the
+        * hypervisor by calling savic_register_gpa(). Before executing
+        * VMRUN, the hypervisor makes use of this information to make sure
+        * the APIC backing page is mapped in NPT.
+        */
+       res = savic_register_gpa(gpa);
+       if (res != ES_OK)
+               snp_abort();
+}
+
 static int savic_probe(void)
 {
        if (!cc_platform_has(CC_ATTR_SNP_SECURE_AVIC))
@@ -30,6 +60,10 @@ static int savic_probe(void)
                /* unreachable */
        }
 
+       savic_page = alloc_percpu(struct secure_avic_page);
+       if (!savic_page)
+               snp_abort();
+
        return 1;
 }
 
@@ -38,6 +72,7 @@ static struct apic apic_x2apic_savic __ro_after_init = {
        .name                           = "secure avic x2apic",
        .probe                          = savic_probe,
        .acpi_madt_oem_check            = savic_acpi_madt_oem_check,
+       .setup                          = savic_setup,
 
        .dest_mode_logical              = false,