OvmfPkg/MemEncryptSevLib: find pages of initial SMRAM save state map

In the next three patches, we're going to modify three modules under
OvmfPkg. When OVMF is built with -D SMM_REQUIRE and runs in an SEV guest,
each affected module will have to know the page range that covers the
initial (pre-SMBASE relocation) SMRAM save state map. Add a helper
function to MemEncryptSevLib that calculates the "base address" and
"number of pages" constants for this page range.

(In a RELEASE build -- i.e., with assertions disabled and optimization
enabled --, the helper function can be compiled to store two constants
determined at compile time.)

Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Brijesh Singh <brijesh.singh@amd.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Tested-by: Brijesh Singh <brijesh.singh@amd.com>
Reviewed-by: Brijesh Singh <brijesh.singh@amd.com>

2 files changed, 55 insertions, 0 deletions

diff --git a/OvmfPkg/Library/BaseMemEncryptSevLib/BaseMemEncryptSevLib.inf b/OvmfPkg/Library/BaseMemEncryptSevLib/BaseMemEncryptSevLib.inf
index 2f0a2392a7..464fe1f33e 100644
--- a/OvmfPkg/Library/BaseMemEncryptSevLib/BaseMemEncryptSevLib.inf
+++ b/OvmfPkg/Library/BaseMemEncryptSevLib/BaseMemEncryptSevLib.inf
@@ -51,3 +51,7 @@
   CpuLib

   DebugLib

   MemoryAllocationLib

+  PcdLib

+

+[FeaturePcd]

+  gUefiOvmfPkgTokenSpaceGuid.PcdSmmSmramRequire

diff --git a/OvmfPkg/Library/BaseMemEncryptSevLib/MemEncryptSevLibInternal.c b/OvmfPkg/Library/BaseMemEncryptSevLib/MemEncryptSevLibInternal.c
index 7078ab0d3f..b92ba50c61 100644
--- a/OvmfPkg/Library/BaseMemEncryptSevLib/MemEncryptSevLibInternal.c
+++ b/OvmfPkg/Library/BaseMemEncryptSevLib/MemEncryptSevLibInternal.c
@@ -17,9 +17,13 @@
 #include <Library/BaseLib.h>

 #include <Library/DebugLib.h>

 #include <Library/MemEncryptSevLib.h>

+#include <Library/PcdLib.h>

 #include <Register/Amd/Cpuid.h>

 #include <Register/Amd/Msr.h>

 #include <Register/Cpuid.h>

+#include <Register/QemuSmramSaveStateMap.h>

+#include <Register/SmramSaveStateMap.h>

+#include <Uefi/UefiBaseType.h>

 

 STATIC BOOLEAN mSevStatus = FALSE;

 STATIC BOOLEAN mSevStatusChecked = FALSE;

@@ -87,3 +91,50 @@ MemEncryptSevIsEnabled (
 

   return mSevStatus;

 }

+

+

+/**

+  Locate the page range that covers the initial (pre-SMBASE-relocation) SMRAM

+  Save State Map.

+

+  @param[out] BaseAddress     The base address of the lowest-address page that

+                              covers the initial SMRAM Save State Map.

+

+  @param[out] NumberOfPages   The number of pages in the page range that covers

+                              the initial SMRAM Save State Map.

+

+  @retval RETURN_SUCCESS      BaseAddress and NumberOfPages have been set on

+                              output.

+

+  @retval RETURN_UNSUPPORTED  SMM is unavailable.

+**/

+RETURN_STATUS

+EFIAPI

+MemEncryptSevLocateInitialSmramSaveStateMapPages (

+  OUT UINTN *BaseAddress,

+  OUT UINTN *NumberOfPages

+  )

+{

+  UINTN MapStart;

+  UINTN MapEnd;

+  UINTN MapPagesStart; // MapStart rounded down to page boundary

+  UINTN MapPagesEnd;   // MapEnd rounded up to page boundary

+  UINTN MapPagesSize;  // difference between MapPagesStart and MapPagesEnd

+

+  if (!FeaturePcdGet (PcdSmmSmramRequire)) {

+    return RETURN_UNSUPPORTED;

+  }

+

+  MapStart      = SMM_DEFAULT_SMBASE + SMRAM_SAVE_STATE_MAP_OFFSET;

+  MapEnd        = MapStart + sizeof (QEMU_SMRAM_SAVE_STATE_MAP);

+  MapPagesStart = MapStart & ~(UINTN)EFI_PAGE_MASK;

+  MapPagesEnd   = ALIGN_VALUE (MapEnd, EFI_PAGE_SIZE);

+  MapPagesSize  = MapPagesEnd - MapPagesStart;

+

+  ASSERT ((MapPagesSize & EFI_PAGE_MASK) == 0);

+

+  *BaseAddress   = MapPagesStart;

+  *NumberOfPages = MapPagesSize >> EFI_PAGE_SHIFT;

+

+  return RETURN_SUCCESS;

+}