OvmfPkg/SecMain: register GHCB gpa for the SEV-SNP guest

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=3275

The SEV-SNP guest requires that GHCB GPA must be registered before using.
See the GHCB specification section 2.3.2 for more details.

Cc: Michael Roth <michael.roth@amd.com>
Cc: James Bottomley <jejb@linux.ibm.com>
Cc: Min Xu <min.m.xu@intel.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
Cc: Erdem Aktas <erdemaktas@google.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Acked-by: Jiewen Yao <Jiewen.yao@intel.com>
Acked-by: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>

OvmfPkg/Sec/AmdSev.c

@@ -48,6 +48,104 @@ SevEsProtocolFailure (
   CpuDeadLoop ();
 }
 
+/**
+  Determine if SEV-SNP is active.
+
+  @retval TRUE   SEV-SNP is enabled
+  @retval FALSE  SEV-SNP is not enabled
+
+**/
+STATIC
+BOOLEAN
+SevSnpIsEnabled (
+  VOID
+  )
+{
+  MSR_SEV_STATUS_REGISTER  Msr;
+
+  //
+  // Read the SEV_STATUS MSR to determine whether SEV-SNP is active.
+  //
+  Msr.Uint32 = AsmReadMsr32 (MSR_SEV_STATUS);
+
+  //
+  // Check MSR_0xC0010131 Bit 2 (Sev-Snp Enabled)
+  //
+  if (Msr.Bits.SevSnpBit) {
+    return TRUE;
+  }
+
+  return FALSE;
+}
+
+/**
+ Register the GHCB GPA
+
+*/
+STATIC
+VOID
+SevSnpGhcbRegister (
+  EFI_PHYSICAL_ADDRESS  Address
+  )
+{
+  MSR_SEV_ES_GHCB_REGISTER  Msr;
+
+  //
+  // Use the GHCB MSR Protocol to request to register the GPA.
+  //
+  Msr.GhcbPhysicalAddress      = Address & ~EFI_PAGE_MASK;
+  Msr.GhcbGpaRegister.Function = GHCB_INFO_GHCB_GPA_REGISTER_REQUEST;
+  AsmWriteMsr64 (MSR_SEV_ES_GHCB, Msr.GhcbPhysicalAddress);
+
+  AsmVmgExit ();
+
+  Msr.GhcbPhysicalAddress = AsmReadMsr64 (MSR_SEV_ES_GHCB);
+
+  //
+  // If hypervisor responded with a different GPA than requested then fail.
+  //
+  if ((Msr.GhcbGpaRegister.Function != GHCB_INFO_GHCB_GPA_REGISTER_RESPONSE) ||
+      ((Msr.GhcbPhysicalAddress & ~EFI_PAGE_MASK) != Address))
+  {
+    SevEsProtocolFailure (GHCB_TERMINATE_GHCB_GENERAL);
+  }
+}
+
+/**
+ Verify that Hypervisor supports the SNP feature.
+
+ */
+STATIC
+BOOLEAN
+HypervisorSnpFeatureCheck (
+  VOID
+  )
+{
+  MSR_SEV_ES_GHCB_REGISTER  Msr;
+  UINT64                    Features;
+
+  //
+  // Use the GHCB MSR Protocol to query the hypervisor capabilities
+  //
+  Msr.GhcbPhysicalAddress             = 0;
+  Msr.GhcbHypervisorFeatures.Function = GHCB_HYPERVISOR_FEATURES_REQUEST;
+  AsmWriteMsr64 (MSR_SEV_ES_GHCB, Msr.GhcbPhysicalAddress);
+
+  AsmVmgExit ();
+
+  Msr.GhcbPhysicalAddress = AsmReadMsr64 (MSR_SEV_ES_GHCB);
+
+  Features =  RShiftU64 (Msr.GhcbPhysicalAddress, 12);
+
+  if ((Msr.GhcbHypervisorFeatures.Function != GHCB_HYPERVISOR_FEATURES_RESPONSE) ||
+      (!(Features & GHCB_HV_FEATURES_SNP)))
+  {
+    return FALSE;
+  }
+
+  return TRUE;
+}
+
 /**
   Validate the SEV-ES/GHCB protocol level.
 
@@ -89,6 +187,27 @@ SevEsProtocolCheck (
     SevEsProtocolFailure (GHCB_TERMINATE_GHCB_PROTOCOL);
   }
 
+  //
+  // We cannot use the MemEncryptSevSnpIsEnabled () because the
+  // ProcessLibraryConstructorList () is not called yet.
+  //
+  if (SevSnpIsEnabled ()) {
+    //
+    // Check if hypervisor supports the SNP feature
+    //
+    if (!HypervisorSnpFeatureCheck ()) {
+      SevEsProtocolFailure (GHCB_TERMINATE_GHCB_PROTOCOL);
+    }
+
+    //
+    // Unlike the SEV-ES guest, the SNP requires that GHCB GPA must be
+    // registered with the Hypervisor before the use. This can be done
+    // using the new VMGEXIT defined in the GHCB v2. Register the GPA
+    // before it is used.
+    //
+    SevSnpGhcbRegister ((EFI_PHYSICAL_ADDRESS)(UINTN)FixedPcdGet32 (PcdOvmfSecGhcbBase));
+  }
+
   //
   // SEV-ES protocol checking succeeded, set the initial GHCB address
   //