[PATCH v2 2/3] OvmfPkg/BaseMemEncryptLib: Support to issue unencrypted hypercall

["Ashish Kalra" <ashish.kalra@amd.com>]

From: Brijesh Singh <brijesh.singh@amd.com>

By default all the SEV guest memory regions are considered encrypted,
if a guest changes the encryption attribute of the page (e.g mark a
page as decrypted) then notify hypervisor. Hypervisor will need to
track the unencrypted pages. The information will be used during
guest live migration, guest page migration and guest debugging.

Invoke hypercall via the new hypercall library.

This hypercall is used to notify hypervisor when a page is marked as
'decrypted' (i.e C-bit removed).

Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Ard Biesheuvel <ard.biesheuvel@arm.com>

Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
---
 OvmfPkg/Library/BaseMemEncryptSevLib/BaseMemEncryptSevLib.inf |  1 +
 OvmfPkg/Library/BaseMemEncryptSevLib/X64/VirtualMemory.c      | 18 ++++++++++++++++++
 2 files changed, 19 insertions(+)

diff --git a/OvmfPkg/Library/BaseMemEncryptSevLib/BaseMemEncryptSevLib.inf b/OvmfPkg/Library/BaseMemEncryptSevLib/BaseMemEncryptSevLib.inf
index 7c44d09528..95ee707918 100644
--- a/OvmfPkg/Library/BaseMemEncryptSevLib/BaseMemEncryptSevLib.inf
+++ b/OvmfPkg/Library/BaseMemEncryptSevLib/BaseMemEncryptSevLib.inf
@@ -46,6 +46,7 @@
   DebugLib
   MemoryAllocationLib
   PcdLib
+  MemEncryptHypercallLib
 
 [FeaturePcd]
   gUefiOvmfPkgTokenSpaceGuid.PcdSmmSmramRequire
diff --git a/OvmfPkg/Library/BaseMemEncryptSevLib/X64/VirtualMemory.c b/OvmfPkg/Library/BaseMemEncryptSevLib/X64/VirtualMemory.c
index 5e110c84ff..1e670b6200 100644
--- a/OvmfPkg/Library/BaseMemEncryptSevLib/X64/VirtualMemory.c
+++ b/OvmfPkg/Library/BaseMemEncryptSevLib/X64/VirtualMemory.c
@@ -14,6 +14,7 @@
 #include <Library/CpuLib.h>
 #include <Register/Amd/Cpuid.h>
 #include <Register/Cpuid.h>
+#include <Library/MemEncryptHypercallLib.h>
 
 #include "VirtualMemory.h"
 
@@ -589,6 +590,9 @@ SetMemoryEncDec (
   UINT64                         AddressEncMask;
   BOOLEAN                        IsWpEnabled;
   RETURN_STATUS                  Status;
+  UINTN                          Size;
+  BOOLEAN                        CBitChanged;
+  PHYSICAL_ADDRESS               OrigPhysicalAddress;
 
   //
   // Set PageMapLevel4Entry to suppress incorrect compiler/analyzer warnings.
@@ -640,6 +644,10 @@ SetMemoryEncDec (
 
   Status = EFI_SUCCESS;
 
+  Size = Length;
+  CBitChanged = FALSE;
+  OrigPhysicalAddress = PhysicalAddress;
+
   while (Length)
   {
     //
@@ -699,6 +707,7 @@ SetMemoryEncDec (
           ));
         PhysicalAddress += BIT30;
         Length -= BIT30;
+        CBitChanged = TRUE;
       } else {
         //
         // We must split the page
@@ -753,6 +762,7 @@ SetMemoryEncDec (
           SetOrClearCBit (&PageDirectory2MEntry->Uint64, Mode);
           PhysicalAddress += BIT21;
           Length -= BIT21;
+          CBitChanged = TRUE;
         } else {
           //
           // We must split up this page into 4K pages
@@ -795,6 +805,7 @@ SetMemoryEncDec (
         SetOrClearCBit (&PageTableEntry->Uint64, Mode);
         PhysicalAddress += EFI_PAGE_SIZE;
         Length -= EFI_PAGE_SIZE;
+        CBitChanged = TRUE;
       }
     }
   }
@@ -812,6 +823,13 @@ SetMemoryEncDec (
   //
   CpuFlushTlb();
 
+  //
+  // Notify Hypervisor on C-bit status
+  //
+  if (CBitChanged) {
+    SetMemoryEncDecHypercall3 (OrigPhysicalAddress, EFI_SIZE_TO_PAGES(Size), !Mode);
+  }
+
 Done:
   //
   // Restore page table write protection, if any.
-- 
2.17.1