Re: [PATCH] UefiCpuPkg: Bug fix in 5LPage handling

["Michael D Kinney" <michael.d.kinney@intel.com>]

+UefiCpuPkg maintainers/reviewers.


> -----Original Message-----
> From: devel@edk2.groups.io <devel@edk2.groups.io> On Behalf Of Guenzel, Robert
> Sent: Thursday, November 10, 2022 5:51 AM
> To: devel@edk2.groups.io
> Subject: [edk2-devel] [PATCH] UefiCpuPkg: Bug fix in 5LPage handling
> 
> When build in DEBUG, the code asserts that 5LPage support is there
> when the physical address width is larger than 48.
> In a RELEASE build it will just force LA57 to 1 in CR4
> even if CPUID(7).ECX[16] says it is not supported.
> 
> The hang (in the ASSERT) in DEBUG is not warranted as there are
> legal configurations with CPUID(7).ECX[16](==LA57)=0
> and with a physical address width of larger than 48 (like 52).
> 
> This is also supported by this code:
> https://github.com/tianocore/edk2/blob/master/UefiCpuPkg/PiSmmCpuDxeSmm/X64/PageTbl.c#L221
> There (as long as physical address width is smaller or equal to 52)
> any address width above 48 will be reduced to 48 and the
> system can and will work without 5LPaging.
> 
> The forced setting of LA57 in CR4 (in the absence of LA57 in CPUID(7).ECX)
> is a spec violation and should not happen.
> 
> Hence the proposed fix
> a) removes the assert.
> b) only returns TRUE from Is5LevelPagingNeeded if 5LPaging is actually
>    supported by HW.
> 
> Signed-off-by: Robert Guenzel mailto:robert.guenzel@intel.com
> ---
>  UefiCpuPkg/PiSmmCpuDxeSmm/X64/PageTbl.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/UefiCpuPkg/PiSmmCpuDxeSmm/X64/PageTbl.c b/UefiCpuPkg/PiSmmCpuDxeSmm/X64/PageTbl.c
> index 6587212f4e..f8b1ac31f1 100644
> --- a/UefiCpuPkg/PiSmmCpuDxeSmm/X64/PageTbl.c
> +++ b/UefiCpuPkg/PiSmmCpuDxeSmm/X64/PageTbl.c
> @@ -104,8 +104,8 @@ Is5LevelPagingNeeded (
>      ExtFeatureEcx.Bits.FiveLevelPage
>      ));
> 
> -  if (VirPhyAddressSize.Bits.PhysicalAddressBits > 4 * 9 + 12) {
> -    ASSERT (ExtFeatureEcx.Bits.FiveLevelPage == 1);
> +  if ((VirPhyAddressSize.Bits.PhysicalAddressBits > 4 * 9 + 12) &&
> +      (ExtFeatureEcx.Bits.FiveLevelPage == 1)) {
>      return TRUE;
>    } else {
>      return FALSE;
> --
> 2.34.1
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