Re: [PATCH v4 2/4] OvmfPkg/BaseMemEncryptLib: Support to issue unencrypted hypercall


Lendacky, Thomas
 

On 6/21/21 8:57 AM, Ashish Kalra wrote:
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/DxeMemEncryptSevLib.inf | 1 +
OvmfPkg/Library/BaseMemEncryptSevLib/PeiMemEncryptSevLib.inf | 1 +
OvmfPkg/Library/BaseMemEncryptSevLib/X64/PeiDxeVirtualMemory.c | 22 ++++++++++++++++++++
3 files changed, 24 insertions(+)

diff --git a/OvmfPkg/Library/BaseMemEncryptSevLib/DxeMemEncryptSevLib.inf b/OvmfPkg/Library/BaseMemEncryptSevLib/DxeMemEncryptSevLib.inf
index f2e162d680..aefcd7c0f7 100644
--- a/OvmfPkg/Library/BaseMemEncryptSevLib/DxeMemEncryptSevLib.inf
+++ b/OvmfPkg/Library/BaseMemEncryptSevLib/DxeMemEncryptSevLib.inf
@@ -49,6 +49,7 @@
DebugLib
MemoryAllocationLib
PcdLib
+ MemEncryptHypercallLib

[FeaturePcd]
gUefiOvmfPkgTokenSpaceGuid.PcdSmmSmramRequire
diff --git a/OvmfPkg/Library/BaseMemEncryptSevLib/PeiMemEncryptSevLib.inf b/OvmfPkg/Library/BaseMemEncryptSevLib/PeiMemEncryptSevLib.inf
index 03a78c32df..7503f56a0b 100644
--- a/OvmfPkg/Library/BaseMemEncryptSevLib/PeiMemEncryptSevLib.inf
+++ b/OvmfPkg/Library/BaseMemEncryptSevLib/PeiMemEncryptSevLib.inf
@@ -49,6 +49,7 @@
DebugLib
MemoryAllocationLib
PcdLib
+ MemEncryptHypercallLib

[FeaturePcd]
gUefiOvmfPkgTokenSpaceGuid.PcdSmmSmramRequire
diff --git a/OvmfPkg/Library/BaseMemEncryptSevLib/X64/PeiDxeVirtualMemory.c b/OvmfPkg/Library/BaseMemEncryptSevLib/X64/PeiDxeVirtualMemory.c
index c696745f9d..12b3a9fcfb 100644
--- a/OvmfPkg/Library/BaseMemEncryptSevLib/X64/PeiDxeVirtualMemory.c
+++ b/OvmfPkg/Library/BaseMemEncryptSevLib/X64/PeiDxeVirtualMemory.c
@@ -15,6 +15,7 @@
#include <Library/MemEncryptSevLib.h>
#include <Register/Amd/Cpuid.h>
#include <Register/Cpuid.h>
+#include <Library/MemEncryptHypercallLib.h>

#include "VirtualMemory.h"

@@ -585,6 +586,9 @@ SetMemoryEncDec (
UINT64 AddressEncMask;
BOOLEAN IsWpEnabled;
RETURN_STATUS Status;
+ UINTN Size;
+ BOOLEAN CBitChanged;
+ PHYSICAL_ADDRESS OrigPhysicalAddress;

//
// Set PageMapLevel4Entry to suppress incorrect compiler/analyzer warnings.
@@ -636,6 +640,10 @@ SetMemoryEncDec (

Status = EFI_SUCCESS;

+ Size = Length;
+ CBitChanged = FALSE;
+ OrigPhysicalAddress = PhysicalAddress;
+
while (Length != 0)
{
//
@@ -695,6 +703,7 @@ SetMemoryEncDec (
));
PhysicalAddress += BIT30;
Length -= BIT30;
+ CBitChanged = TRUE;
} else {
//
// We must split the page
@@ -749,6 +758,7 @@ SetMemoryEncDec (
SetOrClearCBit (&PageDirectory2MEntry->Uint64, Mode);
PhysicalAddress += BIT21;
Length -= BIT21;
+ CBitChanged = TRUE;
} else {
//
// We must split up this page into 4K pages
@@ -791,6 +801,7 @@ SetMemoryEncDec (
SetOrClearCBit (&PageTableEntry->Uint64, Mode);
PhysicalAddress += EFI_PAGE_SIZE;
Length -= EFI_PAGE_SIZE;
+ CBitChanged = TRUE;
}
}
}
@@ -808,6 +819,17 @@ SetMemoryEncDec (
//
CpuFlushTlb();

+ //
+ // Notify Hypervisor on C-bit status
+ //
+ if (CBitChanged) {
+ SetMemoryEncDecHypercall3 (
+ OrigPhysicalAddress,
+ EFI_SIZE_TO_PAGES(Size),
+ KVM_MAP_GPA_RANGE_ENC_STAT(!Mode)
+ );
+ }
Maybe add a comment here that the "Mode" doesn't care whether the change
was for 4k vs 2mb vs 1gb. It is just tracking the total number of pages
changed (should you just remove those #defines for the page sizes then?)
which can be done by calculating everything at the 4k level.

Thanks,
Tom

+
Done:
//
// Restore page table write protection, if any.

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