[RFC PATCH v4 15/27] OvmfPkg/BaseMemEncryptSevLib: skip the pre-validated system RAM

["Brijesh Singh" <brijesh.singh@amd.com>]

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

The MemEncryptSevSnpPreValidateSystemRam() is used for pre-validating the
system RAM. As the boot progress, each phase validates a fixed region of
the RAM. In the PEI phase, the PlatformPei detects all the available RAM
and calls to pre-validate the detected system RAM.

While validating the system RAM in PEI phase, we must skip previously
validated system RAM to avoid the double validation.

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: Laszlo Ersek <lersek@redhat.com>
Cc: Erdem Aktas <erdemaktas@google.com>
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
---
 .../PeiMemEncryptSevLib.inf                   |  2 +
 .../X64/PeiSnpSystemRamValidate.c             | 65 ++++++++++++++++++-
 2 files changed, 66 insertions(+), 1 deletion(-)

diff --git a/OvmfPkg/Library/BaseMemEncryptSevLib/PeiMemEncryptSevLib.inf b/OvmfPkg/Library/BaseMemEncryptSevLib/PeiMemEncryptSevLib.inf
index 0402e49a1028..f4058911e7b6 100644
--- a/OvmfPkg/Library/BaseMemEncryptSevLib/PeiMemEncryptSevLib.inf
+++ b/OvmfPkg/Library/BaseMemEncryptSevLib/PeiMemEncryptSevLib.inf
@@ -58,3 +58,5 @@ [FeaturePcd]
 
 [FixedPcd]
   gUefiCpuPkgTokenSpaceGuid.PcdSevEsWorkAreaBase
+  gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSnpHypervisorPreValidatedEnd
+  gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSnpHypervisorPreValidatedStart
diff --git a/OvmfPkg/Library/BaseMemEncryptSevLib/X64/PeiSnpSystemRamValidate.c b/OvmfPkg/Library/BaseMemEncryptSevLib/X64/PeiSnpSystemRamValidate.c
index 64aab7f45b6d..3e692a3b869d 100644
--- a/OvmfPkg/Library/BaseMemEncryptSevLib/X64/PeiSnpSystemRamValidate.c
+++ b/OvmfPkg/Library/BaseMemEncryptSevLib/X64/PeiSnpSystemRamValidate.c
@@ -14,6 +14,44 @@
 
 #include "SnpPageStateChange.h"
 
+typedef struct {
+  UINT64    StartAddress;
+  UINT64    EndAddress;
+} SNP_PRE_VALIDATED_RANGE;
+
+STATIC SNP_PRE_VALIDATED_RANGE mPreValidatedRange[] = {
+  // This range is pre-validated by the Hypervisor.
+  {
+    FixedPcdGet32 (PcdOvmfSnpHypervisorPreValidatedStart),
+    FixedPcdGet32 (PcdOvmfSnpHypervisorPreValidatedEnd)
+  }
+};
+
+STATIC
+BOOLEAN
+DetectPreValidatedOverLap (
+  IN    PHYSICAL_ADDRESS            StartAddress,
+  IN    PHYSICAL_ADDRESS            EndAddress,
+  OUT   SNP_PRE_VALIDATED_RANGE     *OverlapRange
+  )
+{
+  UINTN               i;
+
+  //
+  // Check if the specified address range exist in pre-validated array.
+  //
+  for (i = 0; i < ARRAY_SIZE (mPreValidatedRange); i++) {
+    if ((mPreValidatedRange[i].StartAddress < EndAddress) &&
+        (StartAddress < mPreValidatedRange[i].EndAddress)) {
+      OverlapRange->StartAddress = mPreValidatedRange[i].StartAddress;
+      OverlapRange->EndAddress = mPreValidatedRange[i].EndAddress;
+      return TRUE;
+    }
+  }
+
+  return FALSE;
+}
+
 /**
   Pre-validate the system RAM when SEV-SNP is enabled in the guest VM.
 
@@ -28,9 +66,34 @@ MemEncryptSevSnpPreValidateSystemRam (
   IN UINTN                              NumPages
   )
 {
+  PHYSICAL_ADDRESS          EndAddress;
+  SNP_PRE_VALIDATED_RANGE   OverlapRange;
+
   if (!MemEncryptSevSnpIsEnabled ()) {
     return;
   }
 
-  InternalSetPageState (BaseAddress, NumPages, SevSnpPagePrivate, TRUE);
+  EndAddress = BaseAddress + EFI_PAGES_TO_SIZE (NumPages);
+
+  while (BaseAddress < EndAddress) {
+    //
+    // Check if the range overlaps with the pre-validated ranges.
+    //
+    if (DetectPreValidatedOverLap (BaseAddress, EndAddress, &OverlapRange)) {
+      // Validate the non-overlap regions.
+      if (BaseAddress < OverlapRange.StartAddress) {
+        NumPages = EFI_SIZE_TO_PAGES (OverlapRange.StartAddress - BaseAddress);
+
+        InternalSetPageState (BaseAddress, NumPages, SevSnpPagePrivate, TRUE);
+      }
+
+      BaseAddress = OverlapRange.EndAddress;
+      continue;
+    }
+
+    // Validate the remaining pages.
+    NumPages = EFI_SIZE_TO_PAGES (EndAddress - BaseAddress);
+    InternalSetPageState (BaseAddress, NumPages, SevSnpPagePrivate, TRUE);
+    BaseAddress = EndAddress;
+  }
 }
-- 
2.17.1