x86/sev: Allow for use of the early boot GHCB for PSC requests

Using a GHCB for a page stage change (as opposed to the MSR protocol)
allows for multiple pages to be processed in a single request. In prep
for early PSC requests in support of unaccepted memory, update the
invocation of vmgexit_psc() to be able to use the early boot GHCB and not
just the per-CPU GHCB structure.

In order to use the proper GHCB (early boot vs per-CPU), set a flag that
indicates when the per-CPU GHCBs are available and registered. For APs,
the per-CPU GHCBs are created before they are started and registered upon
startup, so this flag can be used globally for the BSP and APs instead of
creating a per-CPU flag. This will allow for a significant reduction in
the number of MSR protocol page state change requests when accepting
memory.

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/d6cbb21f87f81eb8282dd3bf6c34d9698c8a4bbc.1686063086.git.thomas.lendacky@amd.com

diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index 7b0144acd7bfbe522081cc04e82b4897132718c3..973756c89dac83d615aa3b045bd2301443cadc2b 100644 (file)
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -119,7 +119,19 @@ static DEFINE_PER_CPU(struct sev_es_save_area *, sev_vmsa);
 
 struct sev_config {
        __u64 debug             : 1,
-             __reserved        : 63;
+
+             /*
+              * A flag used by __set_pages_state() that indicates when the
+              * per-CPU GHCB has been created and registered and thus can be
+              * used by the BSP instead of the early boot GHCB.
+              *
+              * For APs, the per-CPU GHCB is created before they are started
+              * and registered upon startup, so this flag can be used globally
+              * for the BSP and APs.
+              */
+             ghcbs_initialized : 1,
+
+             __reserved        : 62;
 };
 
 static struct sev_config sev_cfg __read_mostly;
@@ -662,7 +674,7 @@ static void pvalidate_pages(unsigned long vaddr, unsigned long npages, bool vali
        }
 }
 
-static void __init early_set_pages_state(unsigned long paddr, unsigned long npages, enum psc_op op)
+static void early_set_pages_state(unsigned long paddr, unsigned long npages, enum psc_op op)
 {
        unsigned long paddr_end;
        u64 val;
@@ -756,26 +768,13 @@ void __init snp_prep_memory(unsigned long paddr, unsigned int sz, enum psc_op op
                WARN(1, "invalid memory op %d\n", op);
 }
 
-static int vmgexit_psc(struct snp_psc_desc *desc)
+static int vmgexit_psc(struct ghcb *ghcb, struct snp_psc_desc *desc)
 {
        int cur_entry, end_entry, ret = 0;
        struct snp_psc_desc *data;
-       struct ghcb_state state;
        struct es_em_ctxt ctxt;
-       unsigned long flags;
-       struct ghcb *ghcb;
 
-       /*
-        * __sev_get_ghcb() needs to run with IRQs disabled because it is using
-        * a per-CPU GHCB.
-        */
-       local_irq_save(flags);
-
-       ghcb = __sev_get_ghcb(&state);
-       if (!ghcb) {
-               ret = 1;
-               goto out_unlock;
-       }
+       vc_ghcb_invalidate(ghcb);
 
        /* Copy the input desc into GHCB shared buffer */
        data = (struct snp_psc_desc *)ghcb->shared_buffer;
@@ -832,20 +831,18 @@ static int vmgexit_psc(struct snp_psc_desc *desc)
        }
 
 out:
-       __sev_put_ghcb(&state);
-
-out_unlock:
-       local_irq_restore(flags);
-
        return ret;
 }
 
 static void __set_pages_state(struct snp_psc_desc *data, unsigned long vaddr,
                              unsigned long vaddr_end, int op)
 {
+       struct ghcb_state state;
        struct psc_hdr *hdr;
        struct psc_entry *e;
+       unsigned long flags;
        unsigned long pfn;
+       struct ghcb *ghcb;
        int i;
 
        hdr = &data->hdr;
@@ -875,8 +872,20 @@ static void __set_pages_state(struct snp_psc_desc *data, unsigned long vaddr,
                i++;
        }
 
-       if (vmgexit_psc(data))
+       local_irq_save(flags);
+
+       if (sev_cfg.ghcbs_initialized)
+               ghcb = __sev_get_ghcb(&state);
+       else
+               ghcb = boot_ghcb;
+
+       if (!ghcb || vmgexit_psc(ghcb, data))
                sev_es_terminate(SEV_TERM_SET_LINUX, GHCB_TERM_PSC);
+
+       if (sev_cfg.ghcbs_initialized)
+               __sev_put_ghcb(&state);
+
+       local_irq_restore(flags);
 }
 
 static void set_pages_state(unsigned long vaddr, unsigned long npages, int op)
@@ -884,6 +893,10 @@ static void set_pages_state(unsigned long vaddr, unsigned long npages, int op)
        unsigned long vaddr_end, next_vaddr;
        struct snp_psc_desc desc;
 
+       /* Use the MSR protocol when a GHCB is not available. */
+       if (!boot_ghcb)
+               return early_set_pages_state(__pa(vaddr), npages, op);
+
        vaddr = vaddr & PAGE_MASK;
        vaddr_end = vaddr + (npages << PAGE_SHIFT);
 
@@ -1261,6 +1274,8 @@ void setup_ghcb(void)
                if (cc_platform_has(CC_ATTR_GUEST_SEV_SNP))
                        snp_register_per_cpu_ghcb();
 
+               sev_cfg.ghcbs_initialized = true;
+
                return;
        }