Currently OVMF tries to rely on the base size advertised via the CPUID
table entries corresponding to leaf 0xD, sub-leafs 0x0/0x1. This will
generally work for KVM guests, but might not for other SEV-SNP
hypervisor implementations. Make the handling more robust by simply
using the base area size documented by the APM.

Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
Acked-by: Jiewen Yao <jiewen.yao@intel.com>
Signed-off-by: Michael Roth <michael.roth@amd.com>
---
 OvmfPkg/Library/CcExitLib/CcExitVcHandler.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/OvmfPkg/Library/CcExitLib/CcExitVcHandler.c b/OvmfPkg/Library/CcExitLib/CcExitVcHandler.c
index 94f0c4872c..0fc30f7bc4 100644
--- a/OvmfPkg/Library/CcExitLib/CcExitVcHandler.c
+++ b/OvmfPkg/Library/CcExitLib/CcExitVcHandler.c
@@ -1114,8 +1114,6 @@ SnpEnabled (
 

   @param[in]      XFeaturesEnabled  Bit-mask of enabled XSAVE features/areas as

                                     indicated by XCR0/MSR_IA32_XSS bits

-  @param[in]      XSaveBaseSize     Base/legacy XSAVE area size (e.g. when

-                                    XCR0 is 1)

   @param[in, out] XSaveSize         Pointer to storage for calculated XSAVE area

                                     size

   @param[in]      Compacted         Whether or not the calculation is for the

@@ -1130,7 +1128,6 @@ STATIC
 BOOLEAN

 GetCpuidXSaveSize (

   IN     UINT64   XFeaturesEnabled,

-  IN     UINT32   XSaveBaseSize,

   IN OUT UINT32   *XSaveSize,

   IN     BOOLEAN  Compacted

   )

@@ -1139,7 +1136,10 @@ GetCpuidXSaveSize (
   UINT64              XFeaturesFound = 0;

   UINT32              Idx;

 

-  *XSaveSize = XSaveBaseSize;

+  //

+  // The base/legacy XSave size is documented to be 0x240 in the APM.

+  //

+  *XSaveSize = 0x240;

   CpuidInfo  = (SEV_SNP_CPUID_INFO *)(UINT64)PcdGet32 (PcdOvmfCpuidBase);

 

   for (Idx = 0; Idx < CpuidInfo->Count; Idx++) {

@@ -1355,7 +1355,6 @@ GetCpuidFw (
 

     if (!GetCpuidXSaveSize (

            XCr0 | XssMsr.Uint64,

-           *Ebx,

            &XSaveSize,

            Compacted

            ))

-- 
2.25.1



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On Wed, Mar 15, 2023 at 04:57:47PM -0500, Michael Roth wrote:
> Currently OVMF tries to rely on the base size advertised via the CPUID
> table entries corresponding to leaf 0xD, sub-leafs 0x0/0x1. This will
> generally work for KVM guests, but might not for other SEV-SNP
> hypervisor implementations. Make the handling more robust by simply
> using the base area size documented by the APM.
> 
> Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
> Acked-by: Jiewen Yao <jiewen.yao@intel.com>
> Signed-off-by: Michael Roth <michael.roth@amd.com>

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



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