Re: [Patch] UefiCpuPkg/S3Resume2Pei: disable paging before creating new page table.

["Ni, Ruiyu" <ruiyu.ni@Intel.com>]

On 10/9/2018 4:09 PM, Laszlo Ersek wrote:
>>
>> Two comments:
>> 1. We'd better not map the PcdCpuStackGuard to paging-enable. Maybe some
>> other feature also enables the paging in PEI phase but the
>> PcdCpuStackGuard is FALSE.
> 
> I think I agree.
> 
>> 2. When PEI is in 64bit mode, disabling paging may not work because
>> paging-enable is a must in 64bit mode.
> 
> I think this case is academic. S3Resume2Pei does not support 64-bit PEI
> with SMM enabled. This is why we have commit 5133d1f1d297 ("OvmfPkg:
> replace README fine print about X64 SMM S3 with PlatformPei check",
> 2015-11-30) in OVMF.

I found that commit. I just checked S3Resume2Pei module. It does assumes 
it's running in 32bit mode. And CpuS3.c also assumes S3Resume2Pei is 
running in 32bit mode.

> 
> Anyway, I'm making this comment in the general sense only. I'm not
> suggesting that we disable paging unconditionally. Actually, I believe,
> I will suggest (under the v3 posting) restricting the write to CR0 even
> more.
Why?

> 
> Thanks!
> Laszlo
> 
>>
>>>>          AsmWriteCr3 ((UINTN)SmmS3ResumeState->SmmS3Cr3);
>>>>
>>>>          //
>>>> diff --git a/UefiCpuPkg/Universal/Acpi/S3Resume2Pei/S3Resume2Pei.inf
>>>> b/UefiCpuPkg/Universal/Acpi/S3Resume2Pei/S3Resume2Pei.inf
>>>> index 6ce1bf944c..0f131d19df 100644
>>>> --- a/UefiCpuPkg/Universal/Acpi/S3Resume2Pei/S3Resume2Pei.inf
>>>> +++ b/UefiCpuPkg/Universal/Acpi/S3Resume2Pei/S3Resume2Pei.inf
>>>> @@ -90,6 +90,7 @@
>>>>    [Pcd]
>>>>      gEfiMdeModulePkgTokenSpaceGuid.PcdUse1GPageTable  ##
>>>> SOMETIMES_CONSUMES
>>>>
>>>> gEfiMdeModulePkgTokenSpaceGuid.PcdPteMemoryEncryptionAddressOrM
>>>> ask    ## CONSUMES
>>>> +
>>>> gEfiMdeModulePkgTokenSpaceGuid.PcdCpuStackGuard                       ##
>>>> CONSUMES
>>>>
>>>>    [Depex]
>>>>      TRUE
>>>> -- 
>>>> 2.15.0.windows.1
>>>>
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>>
> 
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-- 
Thanks,
Ray