[PATCH 0/2] SEV BaseMemEncryptLib cleanup

[PATCH 0/2] SEV BaseMemEncryptLib cleanup

[Brijesh Singh]

This is the first of cleanup for SEV MemEncryptLib. The library uses
the CPUID followed by the MSR read to determine whether SEV is enabled.

Now that we have a workarea concept, the logic can be simplified to
store the msr status in workarea and use that to build PCDs and then
later simply use the PCDs instead of going through the CPUID and RDMSR.

The complete branch is available at
  https://github.com/codomania/edk2/tree/sev-workarea-cleanup

Brijesh Singh (2):
  OvmfPkg/ResetVector: cache the SEV status MSR value in workarea
  OvmfPkg/BaseMemEncryptLib: use the SEV_STATUS MSR value from workarea

 .../DxeMemEncryptSevLib.inf                   |   1 +
 .../PeiMemEncryptSevLib.inf                   |   1 +
 .../SecMemEncryptSevLib.inf                   |   1 +
 OvmfPkg/Include/WorkArea.h                    |  12 +-
 .../DxeMemEncryptSevLibInternal.c             | 142 ++++++++----------
 .../PeiMemEncryptSevLibInternal.c             | 139 ++++++-----------
 .../SecMemEncryptSevLibInternal.c             |  80 +++++-----
 OvmfPkg/Sec/AmdSev.c                          |   2 +-
 OvmfPkg/ResetVector/Ia32/AmdSev.asm           |  38 +++--
 OvmfPkg/ResetVector/Ia32/Flat32ToFlat64.asm   |   3 +-
 OvmfPkg/ResetVector/ResetVector.nasmb         |   3 +
 11 files changed, 189 insertions(+), 233 deletions(-)

-- 
2.25.1

[PATCH 1/2] OvmfPkg/ResetVector: cache the SEV status MSR value in workarea

[Brijesh Singh]

In order to probe the SEV feature the BaseMemEncryptLib and Reset vector
reads the SEV_STATUS MSR. Cache the value on the first read in the
workarea. In the next patches the value saved in the workarea will
be used by the BaseMemEncryptLib. This not only eliminates the extra
MSR reads it also helps cleaning up the code in BaseMemEncryptLib.

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>
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
---
 OvmfPkg/Include/WorkArea.h                  | 12 +++++--
 OvmfPkg/Sec/AmdSev.c                        |  2 +-
 OvmfPkg/ResetVector/Ia32/AmdSev.asm         | 38 +++++++++++++--------
 OvmfPkg/ResetVector/Ia32/Flat32ToFlat64.asm |  3 +-
 OvmfPkg/ResetVector/ResetVector.nasmb       |  3 ++
 5 files changed, 39 insertions(+), 19 deletions(-)

diff --git a/OvmfPkg/Include/WorkArea.h b/OvmfPkg/Include/WorkArea.h
index ce60d97aa886..d982e026def7 100644
--- a/OvmfPkg/Include/WorkArea.h
+++ b/OvmfPkg/Include/WorkArea.h
@@ -46,12 +46,20 @@ typedef struct _CONFIDENTIAL_COMPUTING_WORK_AREA_HEADER {
 // any changes must stay in sync with its usage.
 //
 typedef struct _SEC_SEV_ES_WORK_AREA {
-  UINT8     SevEsEnabled;
-  UINT8     Reserved1[7];
+  //
+  // Hold the SevStatus MSR value read by OvmfPkg/ResetVector/Ia32/AmdSev.c
+  //
+  UINT64    SevStatusMsrValue;
 
   UINT64    RandomData;
 
   UINT64    EncryptionMask;
+
+  //
+  // Indicator that the VC handler is called. It is used during the SevFeature
+  // detection in OvmfPkg/ResetVector/Ia32/AmdSev.c
+  //
+  UINT8     ReceivedVc;
 } SEC_SEV_ES_WORK_AREA;
 
 //
diff --git a/OvmfPkg/Sec/AmdSev.c b/OvmfPkg/Sec/AmdSev.c
index 499d0c27d8fa..d8fd35650d7d 100644
--- a/OvmfPkg/Sec/AmdSev.c
+++ b/OvmfPkg/Sec/AmdSev.c
@@ -278,7 +278,7 @@ SevEsIsEnabled (
 
   SevEsWorkArea = (SEC_SEV_ES_WORK_AREA *)FixedPcdGet32 (PcdSevEsWorkAreaBase);
 
-  return (SevEsWorkArea->SevEsEnabled != 0);
+  return ((SevEsWorkArea->SevStatusMsrValue & BIT1) != 0);
 }
 
 /**
diff --git a/OvmfPkg/ResetVector/Ia32/AmdSev.asm b/OvmfPkg/ResetVector/Ia32/AmdSev.asm
index 1f827da3b929..864d68385342 100644
--- a/OvmfPkg/ResetVector/Ia32/AmdSev.asm
+++ b/OvmfPkg/ResetVector/Ia32/AmdSev.asm
@@ -157,8 +157,9 @@ SevClearPageEncMaskForGhcbPage:
     jnz       SevClearPageEncMaskForGhcbPageExit
 
     ; Check if SEV-ES is enabled
-    cmp       byte[SEV_ES_WORK_AREA], 1
-    jnz       SevClearPageEncMaskForGhcbPageExit
+    mov       ecx, 1
+    bt        [SEV_ES_WORK_AREA_STATUS_MSR], ecx
+    jnc       SevClearPageEncMaskForGhcbPageExit
 
     ;
     ; The initial GHCB will live at GHCB_BASE and needs to be un-encrypted.
@@ -219,12 +220,16 @@ GetSevCBitMaskAbove31Exit:
 ; If SEV is disabled then EAX will be zero.
 ;
 CheckSevFeatures:
-    ; Set the first byte of the workarea to zero to communicate to the SEC
-    ; phase that SEV-ES is not enabled. If SEV-ES is enabled, the CPUID
-    ; instruction will trigger a #VC exception where the first byte of the
-    ; workarea will be set to one or, if CPUID is not being intercepted,
-    ; the MSR check below will set the first byte of the workarea to one.
-    mov     byte[SEV_ES_WORK_AREA], 0
+    ;
+    ; Clear the workarea, if SEV is enabled then later part of routine
+    ; will populate the workarea fields.
+    ;
+    mov    ecx, SEV_ES_WORK_AREA_SIZE
+    mov    eax, SEV_ES_WORK_AREA
+ClearSevEsWorkArea:
+    mov    byte [eax], 0
+    inc    eax
+    loop   ClearSevEsWorkArea
 
     ;
     ; Set up exception handlers to check for SEV-ES
@@ -265,6 +270,10 @@ CheckSevFeatures:
     ; Set the work area header to indicate that the SEV is enabled
     mov     byte[WORK_AREA_GUEST_TYPE], 1
 
+    ; Save the SevStatus MSR value in the workarea
+    mov     [SEV_ES_WORK_AREA_STATUS_MSR], eax
+    mov     [SEV_ES_WORK_AREA_STATUS_MSR + 4], edx
+
     ; Check for SEV-ES memory encryption feature:
     ; CPUID  Fn8000_001F[EAX] - Bit 3
     ;   CPUID raises a #VC exception if running as an SEV-ES guest
@@ -280,10 +289,6 @@ CheckSevFeatures:
     bt        eax, 1
     jnc       GetSevEncBit
 
-    ; Set the first byte of the workarea to one to communicate to the SEC
-    ; phase that SEV-ES is enabled.
-    mov       byte[SEV_ES_WORK_AREA], 1
-
 GetSevEncBit:
     ; Get pte bit position to enable memory encryption
     ; CPUID Fn8000_001F[EBX] - Bits 5:0
@@ -313,7 +318,10 @@ NoSev:
     ;
     ; Perform an SEV-ES sanity check by seeing if a #VC exception occurred.
     ;
-    cmp       byte[SEV_ES_WORK_AREA], 0
+    ; If SEV-ES is enabled, the CPUID instruction will trigger a #VC exception
+    ; where the RECEIVED_VC offset in the workarea will be set to one.
+    ;
+    cmp       byte[SEV_ES_WORK_AREA_RECEIVED_VC], 0
     jz        NoSevPass
 
     ;
@@ -407,9 +415,9 @@ SevEsIdtVmmComm:
     ; If we're here, then we are an SEV-ES guest and this
     ; was triggered by a CPUID instruction
     ;
-    ; Set the first byte of the workarea to one to communicate that
+    ; Set the recievedVc field in the workarea to communicate that
     ; a #VC was taken.
-    mov     byte[SEV_ES_WORK_AREA], 1
+    mov     byte[SEV_ES_WORK_AREA_RECEIVED_VC], 1
 
     pop     ecx                     ; Error code
     cmp     ecx, 0x72               ; Be sure it was CPUID
diff --git a/OvmfPkg/ResetVector/Ia32/Flat32ToFlat64.asm b/OvmfPkg/ResetVector/Ia32/Flat32ToFlat64.asm
index eb3546668ef8..c5c683ebed3e 100644
--- a/OvmfPkg/ResetVector/Ia32/Flat32ToFlat64.asm
+++ b/OvmfPkg/ResetVector/Ia32/Flat32ToFlat64.asm
@@ -42,7 +42,8 @@ Transition32FlatTo64Flat:
     ;
     xor     ebx, ebx
 
-    cmp     byte[SEV_ES_WORK_AREA], 0
+    mov     ecx, 1
+    bt      [SEV_ES_WORK_AREA_STATUS_MSR], ecx
     jz      EnablePaging
 
     ;
diff --git a/OvmfPkg/ResetVector/ResetVector.nasmb b/OvmfPkg/ResetVector/ResetVector.nasmb
index cc364748b592..9421f4818907 100644
--- a/OvmfPkg/ResetVector/ResetVector.nasmb
+++ b/OvmfPkg/ResetVector/ResetVector.nasmb
@@ -100,8 +100,11 @@
   %define GHCB_BASE (FixedPcdGet32 (PcdOvmfSecGhcbBase))
   %define GHCB_SIZE (FixedPcdGet32 (PcdOvmfSecGhcbSize))
   %define SEV_ES_WORK_AREA (FixedPcdGet32 (PcdSevEsWorkAreaBase))
+  %define SEV_ES_WORK_AREA_SIZE 25
+  %define SEV_ES_WORK_AREA_STATUS_MSR (FixedPcdGet32 (PcdSevEsWorkAreaBase))
   %define SEV_ES_WORK_AREA_RDRAND (FixedPcdGet32 (PcdSevEsWorkAreaBase) + 8)
   %define SEV_ES_WORK_AREA_ENC_MASK (FixedPcdGet32 (PcdSevEsWorkAreaBase) + 16)
+  %define SEV_ES_WORK_AREA_RECEIVED_VC (FixedPcdGet32 (PcdSevEsWorkAreaBase) + 24)
   %define SEV_ES_VC_TOP_OF_STACK (FixedPcdGet32 (PcdOvmfSecPeiTempRamBase) + FixedPcdGet32 (PcdOvmfSecPeiTempRamSize))
   %define SEV_SNP_SECRETS_BASE  (FixedPcdGet32 (PcdOvmfSnpSecretsBase))
   %define SEV_SNP_SECRETS_SIZE  (FixedPcdGet32 (PcdOvmfSnpSecretsSize))
-- 
2.25.1

[PATCH 2/2] OvmfPkg/BaseMemEncryptLib: use the SEV_STATUS MSR value from workarea

[Brijesh Singh]

Improve the MemEncryptSev{Es,Snp}IsEnabled() to use the SEV_STATUS MSR
value saved in the workarea. Since workarea is valid until the PEI phase,
so, for the Dxe phase use the PcdConfidentialComputingGuestAttr to
determine which SEV technology is enabled.

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>
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
---
 .../DxeMemEncryptSevLib.inf                   |   1 +
 .../PeiMemEncryptSevLib.inf                   |   1 +
 .../SecMemEncryptSevLib.inf                   |   1 +
 .../DxeMemEncryptSevLibInternal.c             | 142 ++++++++----------
 .../PeiMemEncryptSevLibInternal.c             | 139 ++++++-----------
 .../SecMemEncryptSevLibInternal.c             |  80 +++++-----
 6 files changed, 150 insertions(+), 214 deletions(-)

diff --git a/OvmfPkg/Library/BaseMemEncryptSevLib/DxeMemEncryptSevLib.inf b/OvmfPkg/Library/BaseMemEncryptSevLib/DxeMemEncryptSevLib.inf
index f613bb314f5f..35b7d519d938 100644
--- a/OvmfPkg/Library/BaseMemEncryptSevLib/DxeMemEncryptSevLib.inf
+++ b/OvmfPkg/Library/BaseMemEncryptSevLib/DxeMemEncryptSevLib.inf
@@ -58,3 +58,4 @@ [FeaturePcd]
 
 [Pcd]
   gEfiMdeModulePkgTokenSpaceGuid.PcdPteMemoryEncryptionAddressOrMask
+  gEfiMdePkgTokenSpaceGuid.PcdConfidentialComputingGuestAttr
diff --git a/OvmfPkg/Library/BaseMemEncryptSevLib/PeiMemEncryptSevLib.inf b/OvmfPkg/Library/BaseMemEncryptSevLib/PeiMemEncryptSevLib.inf
index 50c83859d7e7..714da3323765 100644
--- a/OvmfPkg/Library/BaseMemEncryptSevLib/PeiMemEncryptSevLib.inf
+++ b/OvmfPkg/Library/BaseMemEncryptSevLib/PeiMemEncryptSevLib.inf
@@ -58,6 +58,7 @@ [FeaturePcd]
 
 [FixedPcd]
   gUefiCpuPkgTokenSpaceGuid.PcdSevEsWorkAreaBase
+  gUefiOvmfPkgTokenSpaceGuid.PcdOvmfWorkAreaBase
   gUefiOvmfPkgTokenSpaceGuid.PcdOvmfPeiMemFvBase
   gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecPageTablesBase
   gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecValidatedEnd
diff --git a/OvmfPkg/Library/BaseMemEncryptSevLib/SecMemEncryptSevLib.inf b/OvmfPkg/Library/BaseMemEncryptSevLib/SecMemEncryptSevLib.inf
index 939af0a91ea4..284e5acc1177 100644
--- a/OvmfPkg/Library/BaseMemEncryptSevLib/SecMemEncryptSevLib.inf
+++ b/OvmfPkg/Library/BaseMemEncryptSevLib/SecMemEncryptSevLib.inf
@@ -52,3 +52,4 @@ [LibraryClasses]
 
 [FixedPcd]
   gUefiCpuPkgTokenSpaceGuid.PcdSevEsWorkAreaBase
+  gUefiOvmfPkgTokenSpaceGuid.PcdOvmfWorkAreaBase
diff --git a/OvmfPkg/Library/BaseMemEncryptSevLib/DxeMemEncryptSevLibInternal.c b/OvmfPkg/Library/BaseMemEncryptSevLib/DxeMemEncryptSevLibInternal.c
index 15fcd5529587..25768daf5467 100644
--- a/OvmfPkg/Library/BaseMemEncryptSevLib/DxeMemEncryptSevLibInternal.c
+++ b/OvmfPkg/Library/BaseMemEncryptSevLib/DxeMemEncryptSevLibInternal.c
@@ -16,83 +16,77 @@
 #include <Register/Amd/Msr.h>
 #include <Register/Cpuid.h>
 #include <Uefi/UefiBaseType.h>
-
-STATIC BOOLEAN  mSevStatus        = FALSE;
-STATIC BOOLEAN  mSevEsStatus      = FALSE;
-STATIC BOOLEAN  mSevSnpStatus     = FALSE;
-STATIC BOOLEAN  mSevStatusChecked = FALSE;
+#include <ConfidentialComputingGuestAttr.h>
 
 STATIC UINT64   mSevEncryptionMask      = 0;
 STATIC BOOLEAN  mSevEncryptionMaskSaved = FALSE;
 
 /**
-  Reads and sets the status of SEV features.
+  The function check if the specified Attr is set.
 
-  **/
+  @param[in]  CurrentAttr   The current attribute.
+  @param[in]  Attr          The attribute to check.
+
+  @retval  TRUE      The specified Attr is set.
+  @retval  FALSE     The specified Attr is not set.
+
+**/
+STATIC
+BOOLEAN
+AmdMemEncryptionAttrCheck (
+  IN  UINT64                             CurrentAttr,
+  IN  CONFIDENTIAL_COMPUTING_GUEST_ATTR  Attr
+  )
+{
+  switch (Attr) {
+    case CCAttrAmdSev:
+      //
+      // SEV is automatically enabled if SEV-ES or SEV-SNP is active.
+      //
+      return CurrentAttr >= CCAttrAmdSev;
+    case CCAttrAmdSevEs:
+      //
+      // SEV-ES is automatically enabled if SEV-SNP is active.
+      //
+      return CurrentAttr >= CCAttrAmdSevEs;
+    case CCAttrAmdSevSnp:
+      return CurrentAttr == CCAttrAmdSevSnp;
+    default:
+      return FALSE;
+  }
+}
+
+/**
+  Check if the specified confidential computing attribute is active.
+
+  @param[in]  Attr          The attribute to check.
+
+  @retval TRUE   The specified Attr is active.
+  @retval FALSE  The specified Attr is not active.
+
+**/
 STATIC
-VOID
+BOOLEAN
 EFIAPI
-InternalMemEncryptSevStatus (
-  VOID
+ConfidentialComputingGuestHas (
+  IN  CONFIDENTIAL_COMPUTING_GUEST_ATTR  Attr
   )
 {
-  UINT32                            RegEax;
-  MSR_SEV_STATUS_REGISTER           Msr;
-  CPUID_MEMORY_ENCRYPTION_INFO_EAX  Eax;
-  BOOLEAN                           ReadSevMsr;
-  UINT64                            EncryptionMask;
-
-  ReadSevMsr = FALSE;
-
-  EncryptionMask = PcdGet64 (PcdPteMemoryEncryptionAddressOrMask);
-  if (EncryptionMask != 0) {
-    //
-    // The MSR has been read before, so it is safe to read it again and avoid
-    // having to validate the CPUID information.
-    //
-    ReadSevMsr = TRUE;
-  } else {
-    //
-    // Check if memory encryption leaf exist
-    //
-    AsmCpuid (CPUID_EXTENDED_FUNCTION, &RegEax, NULL, NULL, NULL);
-    if (RegEax >= CPUID_MEMORY_ENCRYPTION_INFO) {
-      //
-      // CPUID Fn8000_001F[EAX] Bit 1 (Sev supported)
-      //
-      AsmCpuid (CPUID_MEMORY_ENCRYPTION_INFO, &Eax.Uint32, NULL, NULL, NULL);
-
-      if (Eax.Bits.SevBit) {
-        ReadSevMsr = TRUE;
-      }
-    }
-  }
-
-  if (ReadSevMsr) {
-    //
-    // Check MSR_0xC0010131 Bit 0 (Sev Enabled)
-    //
-    Msr.Uint32 = AsmReadMsr32 (MSR_SEV_STATUS);
-    if (Msr.Bits.SevBit) {
-      mSevStatus = TRUE;
-    }
-
-    //
-    // Check MSR_0xC0010131 Bit 1 (Sev-Es Enabled)
-    //
-    if (Msr.Bits.SevEsBit) {
-      mSevEsStatus = TRUE;
-    }
-
-    //
-    // Check MSR_0xC0010131 Bit 2 (Sev-Snp Enabled)
-    //
-    if (Msr.Bits.SevSnpBit) {
-      mSevSnpStatus = TRUE;
-    }
+  UINT64  CurrentAttr;
+
+  //
+  // Get the current CC attribute.
+  //
+  CurrentAttr = PcdGet64 (PcdConfidentialComputingGuestAttr);
+
+  //
+  // If attr is for the AMD group then call AMD specific checks.
+  //
+  if (((RShiftU64 (CurrentAttr, 8)) & 0xff) == 1) {
+    return AmdMemEncryptionAttrCheck (CurrentAttr, Attr);
   }
 
-  mSevStatusChecked = TRUE;
+  return (CurrentAttr == Attr);
 }
 
 /**
@@ -107,11 +101,7 @@ MemEncryptSevSnpIsEnabled (
   VOID
   )
 {
-  if (!mSevStatusChecked) {
-    InternalMemEncryptSevStatus ();
-  }
-
-  return mSevSnpStatus;
+  return ConfidentialComputingGuestHas (CCAttrAmdSevSnp);
 }
 
 /**
@@ -126,11 +116,7 @@ MemEncryptSevEsIsEnabled (
   VOID
   )
 {
-  if (!mSevStatusChecked) {
-    InternalMemEncryptSevStatus ();
-  }
-
-  return mSevEsStatus;
+  return ConfidentialComputingGuestHas (CCAttrAmdSevEs);
 }
 
 /**
@@ -145,11 +131,7 @@ MemEncryptSevIsEnabled (
   VOID
   )
 {
-  if (!mSevStatusChecked) {
-    InternalMemEncryptSevStatus ();
-  }
-
-  return mSevStatus;
+  return ConfidentialComputingGuestHas (CCAttrAmdSev);
 }
 
 /**
diff --git a/OvmfPkg/Library/BaseMemEncryptSevLib/PeiMemEncryptSevLibInternal.c b/OvmfPkg/Library/BaseMemEncryptSevLib/PeiMemEncryptSevLibInternal.c
index d68ff08c3ea6..3f8f91a5da12 100644
--- a/OvmfPkg/Library/BaseMemEncryptSevLib/PeiMemEncryptSevLibInternal.c
+++ b/OvmfPkg/Library/BaseMemEncryptSevLib/PeiMemEncryptSevLibInternal.c
@@ -17,82 +17,51 @@
 #include <Register/Cpuid.h>
 #include <Uefi/UefiBaseType.h>
 
-STATIC BOOLEAN  mSevStatus        = FALSE;
-STATIC BOOLEAN  mSevEsStatus      = FALSE;
-STATIC BOOLEAN  mSevSnpStatus     = FALSE;
-STATIC BOOLEAN  mSevStatusChecked = FALSE;
+/**
+   Read the workarea to determine whether SEV is enabled. If enabled,
+   then return the SevEsWorkArea pointer.
+
+  **/
+STATIC
+SEC_SEV_ES_WORK_AREA *
+EFIAPI
+GetSevEsWorkArea (
+  VOID
+  )
+{
+  OVMF_WORK_AREA  *WorkArea;
+
+  WorkArea = (OVMF_WORK_AREA *)FixedPcdGet32 (PcdOvmfWorkAreaBase);
+
+  //
+  // If its not SEV guest then SevEsWorkArea is not valid.
+  //
+  if ((WorkArea == NULL) || (WorkArea->Header.GuestType != GUEST_TYPE_AMD_SEV)) {
+    return NULL;
+  }
 
-STATIC UINT64   mSevEncryptionMask      = 0;
-STATIC BOOLEAN  mSevEncryptionMaskSaved = FALSE;
+  return (SEC_SEV_ES_WORK_AREA *)FixedPcdGet32 (PcdSevEsWorkAreaBase);
+}
 
 /**
-  Reads and sets the status of SEV features.
+  Read the SEV Status MSR value from the workarea
 
   **/
 STATIC
-VOID
+UINT32
 EFIAPI
 InternalMemEncryptSevStatus (
   VOID
   )
 {
-  UINT32                            RegEax;
-  MSR_SEV_STATUS_REGISTER           Msr;
-  CPUID_MEMORY_ENCRYPTION_INFO_EAX  Eax;
-  BOOLEAN                           ReadSevMsr;
-  SEC_SEV_ES_WORK_AREA              *SevEsWorkArea;
+  SEC_SEV_ES_WORK_AREA  *SevEsWorkArea;
 
-  ReadSevMsr = FALSE;
-
-  SevEsWorkArea = (SEC_SEV_ES_WORK_AREA *)FixedPcdGet32 (PcdSevEsWorkAreaBase);
-  if ((SevEsWorkArea != NULL) && (SevEsWorkArea->EncryptionMask != 0)) {
-    //
-    // The MSR has been read before, so it is safe to read it again and avoid
-    // having to validate the CPUID information.
-    //
-    ReadSevMsr = TRUE;
-  } else {
-    //
-    // Check if memory encryption leaf exist
-    //
-    AsmCpuid (CPUID_EXTENDED_FUNCTION, &RegEax, NULL, NULL, NULL);
-    if (RegEax >= CPUID_MEMORY_ENCRYPTION_INFO) {
-      //
-      // CPUID Fn8000_001F[EAX] Bit 1 (Sev supported)
-      //
-      AsmCpuid (CPUID_MEMORY_ENCRYPTION_INFO, &Eax.Uint32, NULL, NULL, NULL);
-
-      if (Eax.Bits.SevBit) {
-        ReadSevMsr = TRUE;
-      }
-    }
-  }
-
-  if (ReadSevMsr) {
-    //
-    // Check MSR_0xC0010131 Bit 0 (Sev Enabled)
-    //
-    Msr.Uint32 = AsmReadMsr32 (MSR_SEV_STATUS);
-    if (Msr.Bits.SevBit) {
-      mSevStatus = TRUE;
-    }
-
-    //
-    // Check MSR_0xC0010131 Bit 1 (Sev-Es Enabled)
-    //
-    if (Msr.Bits.SevEsBit) {
-      mSevEsStatus = TRUE;
-    }
-
-    //
-    // Check MSR_0xC0010131 Bit 2 (Sev-Snp Enabled)
-    //
-    if (Msr.Bits.SevSnpBit) {
-      mSevSnpStatus = TRUE;
-    }
+  SevEsWorkArea = GetSevEsWorkArea ();
+  if (SevEsWorkArea == NULL) {
+    return 0;
   }
 
-  mSevStatusChecked = TRUE;
+  return (UINT32)(UINTN)SevEsWorkArea->SevStatusMsrValue;
 }
 
 /**
@@ -107,11 +76,11 @@ MemEncryptSevSnpIsEnabled (
   VOID
   )
 {
-  if (!mSevStatusChecked) {
-    InternalMemEncryptSevStatus ();
-  }
+  MSR_SEV_STATUS_REGISTER  Msr;
 
-  return mSevSnpStatus;
+  Msr.Uint32 = InternalMemEncryptSevStatus ();
+
+  return Msr.Bits.SevSnpBit ? TRUE : FALSE;
 }
 
 /**
@@ -126,11 +95,11 @@ MemEncryptSevEsIsEnabled (
   VOID
   )
 {
-  if (!mSevStatusChecked) {
-    InternalMemEncryptSevStatus ();
-  }
+  MSR_SEV_STATUS_REGISTER  Msr;
 
-  return mSevEsStatus;
+  Msr.Uint32 = InternalMemEncryptSevStatus ();
+
+  return Msr.Bits.SevEsBit ? TRUE : FALSE;
 }
 
 /**
@@ -145,11 +114,11 @@ MemEncryptSevIsEnabled (
   VOID
   )
 {
-  if (!mSevStatusChecked) {
-    InternalMemEncryptSevStatus ();
-  }
+  MSR_SEV_STATUS_REGISTER  Msr;
 
-  return mSevStatus;
+  Msr.Uint32 = InternalMemEncryptSevStatus ();
+
+  return Msr.Bits.SevBit ? TRUE : FALSE;
 }
 
 /**
@@ -163,24 +132,12 @@ MemEncryptSevGetEncryptionMask (
   VOID
   )
 {
-  if (!mSevEncryptionMaskSaved) {
-    SEC_SEV_ES_WORK_AREA  *SevEsWorkArea;
+  SEC_SEV_ES_WORK_AREA  *SevEsWorkArea;
 
-    SevEsWorkArea = (SEC_SEV_ES_WORK_AREA *)FixedPcdGet32 (PcdSevEsWorkAreaBase);
-    if (SevEsWorkArea != NULL) {
-      mSevEncryptionMask = SevEsWorkArea->EncryptionMask;
-    } else {
-      CPUID_MEMORY_ENCRYPTION_INFO_EBX  Ebx;
-
-      //
-      // CPUID Fn8000_001F[EBX] Bit 0:5 (memory encryption bit position)
-      //
-      AsmCpuid (CPUID_MEMORY_ENCRYPTION_INFO, NULL, &Ebx.Uint32, NULL, NULL);
-      mSevEncryptionMask = LShiftU64 (1, Ebx.Bits.PtePosBits);
-    }
-
-    mSevEncryptionMaskSaved = TRUE;
+  SevEsWorkArea = GetSevEsWorkArea ();
+  if (SevEsWorkArea == NULL) {
+    return 0;
   }
 
-  return mSevEncryptionMask;
+  return SevEsWorkArea->EncryptionMask;
 }
diff --git a/OvmfPkg/Library/BaseMemEncryptSevLib/SecMemEncryptSevLibInternal.c b/OvmfPkg/Library/BaseMemEncryptSevLib/SecMemEncryptSevLibInternal.c
index 5d912b2a4a5e..80aceba01bcf 100644
--- a/OvmfPkg/Library/BaseMemEncryptSevLib/SecMemEncryptSevLibInternal.c
+++ b/OvmfPkg/Library/BaseMemEncryptSevLib/SecMemEncryptSevLibInternal.c
@@ -18,7 +18,33 @@
 #include <Uefi/UefiBaseType.h>
 
 /**
-  Reads and sets the status of SEV features.
+   Read the workarea to determine whether SEV is enabled. If enabled,
+   then return the SevEsWorkArea pointer.
+
+  **/
+STATIC
+SEC_SEV_ES_WORK_AREA *
+EFIAPI
+GetSevEsWorkArea (
+  VOID
+  )
+{
+  OVMF_WORK_AREA  *WorkArea;
+
+  WorkArea = (OVMF_WORK_AREA *)FixedPcdGet32 (PcdOvmfWorkAreaBase);
+
+  //
+  // If its not SEV guest then SevEsWorkArea is not valid.
+  //
+  if ((WorkArea == NULL) || (WorkArea->Header.GuestType != GUEST_TYPE_AMD_SEV)) {
+    return NULL;
+  }
+
+  return (SEC_SEV_ES_WORK_AREA *)FixedPcdGet32 (PcdSevEsWorkAreaBase);
+}
+
+/**
+  Read the SEV Status MSR value from the workarea
 
   **/
 STATIC
@@ -28,38 +54,14 @@ InternalMemEncryptSevStatus (
   VOID
   )
 {
-  UINT32                            RegEax;
-  CPUID_MEMORY_ENCRYPTION_INFO_EAX  Eax;
-  BOOLEAN                           ReadSevMsr;
-  SEC_SEV_ES_WORK_AREA              *SevEsWorkArea;
+  SEC_SEV_ES_WORK_AREA  *SevEsWorkArea;
 
-  ReadSevMsr = FALSE;
-
-  SevEsWorkArea = (SEC_SEV_ES_WORK_AREA *)FixedPcdGet32 (PcdSevEsWorkAreaBase);
-  if ((SevEsWorkArea != NULL) && (SevEsWorkArea->EncryptionMask != 0)) {
-    //
-    // The MSR has been read before, so it is safe to read it again and avoid
-    // having to validate the CPUID information.
-    //
-    ReadSevMsr = TRUE;
-  } else {
-    //
-    // Check if memory encryption leaf exist
-    //
-    AsmCpuid (CPUID_EXTENDED_FUNCTION, &RegEax, NULL, NULL, NULL);
-    if (RegEax >= CPUID_MEMORY_ENCRYPTION_INFO) {
-      //
-      // CPUID Fn8000_001F[EAX] Bit 1 (Sev supported)
-      //
-      AsmCpuid (CPUID_MEMORY_ENCRYPTION_INFO, &Eax.Uint32, NULL, NULL, NULL);
-
-      if (Eax.Bits.SevBit) {
-        ReadSevMsr = TRUE;
-      }
-    }
+  SevEsWorkArea = GetSevEsWorkArea ();
+  if (SevEsWorkArea == NULL) {
+    return 0;
   }
 
-  return ReadSevMsr ? AsmReadMsr32 (MSR_SEV_STATUS) : 0;
+  return (UINT32)(UINTN)SevEsWorkArea->SevStatusMsrValue;
 }
 
 /**
@@ -130,22 +132,14 @@ MemEncryptSevGetEncryptionMask (
   VOID
   )
 {
-  CPUID_MEMORY_ENCRYPTION_INFO_EBX  Ebx;
-  SEC_SEV_ES_WORK_AREA              *SevEsWorkArea;
-  UINT64                            EncryptionMask;
+  SEC_SEV_ES_WORK_AREA  *SevEsWorkArea;
 
-  SevEsWorkArea = (SEC_SEV_ES_WORK_AREA *)FixedPcdGet32 (PcdSevEsWorkAreaBase);
-  if (SevEsWorkArea != NULL) {
-    EncryptionMask = SevEsWorkArea->EncryptionMask;
-  } else {
-    //
-    // CPUID Fn8000_001F[EBX] Bit 0:5 (memory encryption bit position)
-    //
-    AsmCpuid (CPUID_MEMORY_ENCRYPTION_INFO, NULL, &Ebx.Uint32, NULL, NULL);
-    EncryptionMask = LShiftU64 (1, Ebx.Bits.PtePosBits);
+  SevEsWorkArea = GetSevEsWorkArea ();
+  if (SevEsWorkArea == NULL) {
+    return 0;
   }
 
-  return EncryptionMask;
+  return SevEsWorkArea->EncryptionMask;
 }
 
 /**
-- 
2.25.1

Re: [PATCH 0/2] SEV BaseMemEncryptLib cleanup

[Gerd Hoffmann]

On Wed, Jan 19, 2022 at 05:03:30PM -0600, Brijesh Singh wrote:
> This is the first of cleanup for SEV MemEncryptLib. The library uses
> the CPUID followed by the MSR read to determine whether SEV is enabled.
> 
> Now that we have a workarea concept, the logic can be simplified to
> store the msr status in workarea and use that to build PCDs and then
> later simply use the PCDs instead of going through the CPUID and RDMSR.
> 
> The complete branch is available at
>   https://github.com/codomania/edk2/tree/sev-workarea-cleanup
> 
> Brijesh Singh (2):
>   OvmfPkg/ResetVector: cache the SEV status MSR value in workarea
>   OvmfPkg/BaseMemEncryptLib: use the SEV_STATUS MSR value from workarea

Looks good to me.

Acked-by: Gerd Hoffmann <kraxel@redhat.com>

take care,
  Gerd

Re: [edk2-devel] [PATCH 0/2] SEV BaseMemEncryptLib cleanup

[Brijesh Singh]

On 1/21/22 2:04 AM, Gerd Hoffmann via groups.io wrote:
> On Wed, Jan 19, 2022 at 05:03:30PM -0600, Brijesh Singh wrote:
>> This is the first of cleanup for SEV MemEncryptLib. The library uses
>> the CPUID followed by the MSR read to determine whether SEV is enabled.
>>
>> Now that we have a workarea concept, the logic can be simplified to
>> store the msr status in workarea and use that to build PCDs and then
>> later simply use the PCDs instead of going through the CPUID and RDMSR.
>>
>> The complete branch is available at
>>    https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fcodomania%2Fedk2%2Ftree%2Fsev-workarea-cleanup&data=04%7C01%7Cbrijesh.singh%40amd.com%7C72f26427ada24f9fc2aa08d9dcb4bc74%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637783491097406747%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=DKsibiI3OYAJkR09fMPCUz0JGyh7ZrGJGj55VmO5%2FsQ%3D&reserved=0
>>
>> Brijesh Singh (2):
>>    OvmfPkg/ResetVector: cache the SEV status MSR value in workarea
>>    OvmfPkg/BaseMemEncryptLib: use the SEV_STATUS MSR value from workarea
> 
> Looks good to me.
> 
> Acked-by: Gerd Hoffmann <kraxel@redhat.com>
> 

I ran into a regression for non-SEV guest, let me work to fix and post v2.

-Brijesh