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

[Laszlo Ersek <lersek@redhat.com>]

On 10/09/18 04:15, Ni, Ruiyu wrote:
> On 10/9/2018 10:05 AM, Dong, Eric wrote:
>> Add BZ link for this issue:
>> https://bugzilla.tianocore.org/show_bug.cgi?id=1232
>>
>> Thanks,
>> Eric
>>
>>> -----Original Message-----
>>> From: edk2-devel [mailto:edk2-devel-bounces@lists.01.org] On Behalf Of
>>> Eric Dong
>>> Sent: Tuesday, October 9, 2018 9:51 AM
>>> To: edk2-devel@lists.01.org
>>> Cc: Ni, Ruiyu <ruiyu.ni@intel.com>; Laszlo Ersek <lersek@redhat.com>
>>> Subject: [edk2] [Patch] UefiCpuPkg/S3Resume2Pei: disable paging before
>>> creating new page table.
>>>
>>> PEI Stack Guard needs to enable paging. This might cause #GP in the
>>> transition from 32-bit PEI to 64-bit SMM due to the code trying to
>>> write CR3
>>> register with PML4 page table while the processor is enabled with PAE
>>> paging.
>>>
>>> Simply disabling paging before updating CR3 can solve this conflict.
>>>
>>> Change-Id: I99bfdba5daa48a95a4c4ef97eeca1af086558957
>>> Cc: Ruiyu Ni <ruiyu.ni@intel.com>
>>> Cc: Laszlo Ersek <lersek@redhat.com>
>>> Cc: Jian J Wang <jian.j.wang@intel.com>
>>> Contributed-under: TianoCore Contribution Agreement 1.1 Signed-off-
>>> by:Eric Dong <eric.dong@intel.com>
>>> Signed-off-by: Eric Dong <eric.dong@intel.com>
>>> ---
>>>   UefiCpuPkg/Universal/Acpi/S3Resume2Pei/S3Resume.c       | 7 +++++++
>>>   UefiCpuPkg/Universal/Acpi/S3Resume2Pei/S3Resume2Pei.inf | 1 +
>>>   2 files changed, 8 insertions(+)
>>>
>>> diff --git a/UefiCpuPkg/Universal/Acpi/S3Resume2Pei/S3Resume.c
>>> b/UefiCpuPkg/Universal/Acpi/S3Resume2Pei/S3Resume.c
>>> index f164c1713b..b3bf56e13d 100644
>>> --- a/UefiCpuPkg/Universal/Acpi/S3Resume2Pei/S3Resume.c
>>> +++ b/UefiCpuPkg/Universal/Acpi/S3Resume2Pei/S3Resume.c
>>> @@ -1105,6 +1105,13 @@ S3RestoreConfig2 (
>>>         //
>>>         SetInterruptState (InterruptStatus);
>>>
>>> +      if (PcdGetBool (PcdCpuStackGuard)) {
>>> +        //
>>> +        // Paging already been enabled, to avoid conflict
>>> configuration,
>>> +        // disable paging first anyway.
>>> +        //
>>> +        AsmWriteCr0 (AsmReadCr0 () & (~BIT31));
>>> +      }
> 
> 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.

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.

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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> 
>