Re: [edk2-devel] [PATCH v2 1/1] UefiCpuPkg/BaseXApicX2ApicLib: fix CPUID_V2_EXTENDED_TOPOLOGY detection

["Laszlo Ersek" <lersek@redhat.com>]

On 10/17/23 13:28, Gerd Hoffmann wrote:
> Checking the max cpuid leaf is not enough to figure whenever
> CPUID_V2_EXTENDED_TOPOLOGY is supported.  Intel SDM says:
> 
>    Software must detect the presence of CPUID leaf 1FH by verifying
>    (a) the highest leaf index supported by CPUID is >= 1FH, and
>    (b) CPUID.1FH:EBX[15:0] reports a non-zero value.
> 
> The same is true for CPUID leaf 0BH.
> 
> This patch adds the EBX check to GetProcessorLocation2ByApicId().  The
> patch also fixes the existing check in GetProcessorLocationByApicId() to
> be in line with the spec by looking at bits 15:0.  The comments are
> updated with a quote from the Intel SDM.
> 
> Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2241388
> Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
> ---
>  .../BaseXApicX2ApicLib/BaseXApicX2ApicLib.c   | 21 ++++++++++++++-----
>  1 file changed, 16 insertions(+), 5 deletions(-)
> 
> diff --git a/UefiCpuPkg/Library/BaseXApicX2ApicLib/BaseXApicX2ApicLib.c b/UefiCpuPkg/Library/BaseXApicX2ApicLib/BaseXApicX2ApicLib.c
> index aa4eb11181f6..c0a847583330 100644
> --- a/UefiCpuPkg/Library/BaseXApicX2ApicLib/BaseXApicX2ApicLib.c
> +++ b/UefiCpuPkg/Library/BaseXApicX2ApicLib/BaseXApicX2ApicLib.c
> @@ -1294,11 +1294,12 @@ GetProcessorLocationByApicId (
>        NULL
>        );
>      //
> -    // If CPUID.(EAX=0BH, ECX=0H):EBX returns zero and maximum input value for
> -    // basic CPUID information is greater than 0BH, then CPUID.0BH leaf is not
> -    // supported on that processor.
> +    // Quoting Intel SDM:
> +    // Software must detect the presence of CPUID leaf 0BH by
> +    // verifying (a) the highest leaf index supported by CPUID is >=
> +    // 0BH, and (b) CPUID.0BH:EBX[15:0] reports a non-zero value.
>      //
> -    if (ExtendedTopologyEbx.Uint32 != 0) {
> +    if (ExtendedTopologyEbx.Bits.LogicalProcessors != 0) {
>        TopologyLeafSupported = TRUE;
>  
>        //
> @@ -1424,6 +1425,7 @@ GetProcessorLocation2ByApicId (
>    )
>  {
>    CPUID_EXTENDED_TOPOLOGY_EAX  ExtendedTopologyEax;
> +  CPUID_EXTENDED_TOPOLOGY_EBX  ExtendedTopologyEbx;
>    CPUID_EXTENDED_TOPOLOGY_ECX  ExtendedTopologyEcx;
>    UINT32                       MaxStandardCpuIdIndex;
>    UINT32                       Index;
> @@ -1436,10 +1438,19 @@ GetProcessorLocation2ByApicId (
>    }
>  
>    //
> -  // Get max index of CPUID
> +  // Quoting Intel SDM:
> +  // Software must detect the presence of CPUID leaf 1FH by verifying
> +  // (a) the highest leaf index supported by CPUID is >= 1FH, and (b)
> +  // CPUID.1FH:EBX[15:0] reports a non-zero value.
>    //
>    AsmCpuid (CPUID_SIGNATURE, &MaxStandardCpuIdIndex, NULL, NULL, NULL);
>    if (MaxStandardCpuIdIndex < CPUID_V2_EXTENDED_TOPOLOGY) {
> +    ExtendedTopologyEbx.Bits.LogicalProcessors = 0;
> +  } else {
> +    AsmCpuidEx (CPUID_V2_EXTENDED_TOPOLOGY, 0, NULL, &ExtendedTopologyEbx.Uint32, NULL, NULL);
> +  }
> +
> +  if (ExtendedTopologyEbx.Bits.LogicalProcessors == 0) {
>      if (Die != NULL) {
>        *Die = 0;
>      }

Commit 170d4ce8e90abb1eff03852940a69c9d17f8afe5 (via #4954).

Laszlo



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