The CPUID_EXTENDED_TOPOLOGY CPUID leaf takes a subleaf as input when
returning CPUID information. However, the AsmCpuid() function does not
zero out ECX before the CPUID instruction, so the input leaf is used as
the sub-leaf for the CPUID request and returns erroneous/invalid CPUID
data, since the intent of the request was to get data related to sub-leaf
0. Instead, use AsmCpuidEx() for the CPUID_EXTENDED_TOPOLOGY leaf.

Fixes: d4d7c9ad5fe5 ("UefiCpuPkg/MpInitLib: use BSP to do extended ...")
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
---
 UefiCpuPkg/Library/MpInitLib/AmdSev.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/UefiCpuPkg/Library/MpInitLib/AmdSev.c b/UefiCpuPkg/Library/MpInitLib/AmdSev.c
index bda4960f6fd3..d34f9513e002 100644
--- a/UefiCpuPkg/Library/MpInitLib/AmdSev.c
+++ b/UefiCpuPkg/Library/MpInitLib/AmdSev.c
@@ -256,7 +256,14 @@ FillExchangeInfoDataSevEs (
   if (StdRangeMax >= CPUID_EXTENDED_TOPOLOGY) {
     CPUID_EXTENDED_TOPOLOGY_EBX  ExtTopoEbx;
 
-    AsmCpuid (CPUID_EXTENDED_TOPOLOGY, NULL, &ExtTopoEbx.Uint32, NULL, NULL);
+    AsmCpuidEx (
+      CPUID_EXTENDED_TOPOLOGY,
+      0,
+      NULL,
+      &ExtTopoEbx.Uint32,
+      NULL,
+      NULL
+      );
     ExchangeInfo->ExtTopoAvail = !!ExtTopoEbx.Bits.LogicalProcessors;
   }
 }
-- 
2.42.0



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Reviewed-by: Ray Ni <ray.ni@intel.com>

Thanks,
Ray
> -----Original Message-----
> From: Tom Lendacky <thomas.lendacky@amd.com>
> Sent: Tuesday, November 7, 2023 6:46 AM
> To: devel@edk2.groups.io
> Cc: Dong, Eric <eric.dong@intel.com>; Ni, Ray <ray.ni@intel.com>; Kumar,
> Rahul R <rahul.r.kumar@intel.com>; Gerd Hoffmann <kraxel@redhat.com>;
> Ard Biesheuvel <ardb+tianocore@kernel.org>; Michael Roth
> <michael.roth@amd.com>
> Subject: [PATCH 1/2] UefiCpuPkg/MpInitLib: Use AsmCpuidEx() for
> CPUID_EXTENDED_TOPOLOGY leaf
> 
> The CPUID_EXTENDED_TOPOLOGY CPUID leaf takes a subleaf as input when
> returning CPUID information. However, the AsmCpuid() function does not
> zero out ECX before the CPUID instruction, so the input leaf is used as
> the sub-leaf for the CPUID request and returns erroneous/invalid CPUID
> data, since the intent of the request was to get data related to sub-leaf
> 0. Instead, use AsmCpuidEx() for the CPUID_EXTENDED_TOPOLOGY leaf.
> 
> Fixes: d4d7c9ad5fe5 ("UefiCpuPkg/MpInitLib: use BSP to do extended ...")
> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
> ---
>  UefiCpuPkg/Library/MpInitLib/AmdSev.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/UefiCpuPkg/Library/MpInitLib/AmdSev.c
> b/UefiCpuPkg/Library/MpInitLib/AmdSev.c
> index bda4960f6fd3..d34f9513e002 100644
> --- a/UefiCpuPkg/Library/MpInitLib/AmdSev.c
> +++ b/UefiCpuPkg/Library/MpInitLib/AmdSev.c
> @@ -256,7 +256,14 @@ FillExchangeInfoDataSevEs (
>    if (StdRangeMax >= CPUID_EXTENDED_TOPOLOGY) {
>      CPUID_EXTENDED_TOPOLOGY_EBX  ExtTopoEbx;
> 
> -    AsmCpuid (CPUID_EXTENDED_TOPOLOGY, NULL, &ExtTopoEbx.Uint32,
> NULL, NULL);
> +    AsmCpuidEx (
> +      CPUID_EXTENDED_TOPOLOGY,
> +      0,
> +      NULL,
> +      &ExtTopoEbx.Uint32,
> +      NULL,
> +      NULL
> +      );
>      ExchangeInfo->ExtTopoAvail = !!ExtTopoEbx.Bits.LogicalProcessors;
>    }
>  }
> --
> 2.42.0



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