Re: [edk2-devel] [PATCH v3 00/13] Add SmmRelocationLib

["Lendacky, Thomas via groups.io" <thomas.lendacky=amd.com@groups.io>]

On 4/25/24 01:58, Gerd Hoffmann wrote:
>    Hi,
> 
>> That means the SMMRevId is 0_xx64h for AMD64 processor. But I am not
>> sure what the value is for AMD32 processor. Maybe 0 according to the
>> OVMF logic.
> 
> The smm emulation in the linux kernel uses 0 and 0x64.
> 
>> But, I am very suspicious about the logic in AMD's version as below:
>> --- AMD's version
>>    SmmSaveStateRegisterLma = (UINT8)EFI_MM_SAVE_STATE_REGISTER_LMA_32BIT;
>>
>>    LMAValue = (UINT32)AsmReadMsr64 (EFER_ADDRESS) & LMA;
>>    if (LMAValue) {
>>      SmmSaveStateRegisterLma = (UINT8)EFI_MM_SAVE_STATE_REGISTER_LMA_64BIT;
>>    }
>> ---
>> The above logic detects the current CPU mode and 64bit save state area layout is used if it's running in 64bit.
> 
>> But if a AMD64 CPU runs in 32bit mode, the above logic causes the
>> 32bit save state area layout is used. It's not right!  The save state
>> area layout does not depend on the CPU running mode, but whether it's
>> a legacy CPU or a 64-capable CPU.
> 
> Well, that is not entirely clear to me.  Could it be 64-bit processors
> support both 32-bit and 64-bit format, for backward compatibility
> reasons?
> 
> So OvmfPkgIa32 builds could use the 32-bit format, OvmfPkgX64 builds use
> the 64-bit format, everything works fine?
> 
> The tricky corner case is OvmfPkgIa32X64, where (after applying this
> series) 32-bit PEI should setup things for 64-bit SMM/DXE, and checking
> the current processor mode will not give use the result we need.
> 
>> Jiaxin, I agree that the confusion should be cleaned up by AMD
>> experts. Let's not change any existing behavior.
> 
> Agree.  Tom?

I don't have a lot of experience with SMM. I believe Paolo first ported 
over the support into OVMF and might have more insight?

I'll try to take a look at it when I can, but maybe @Abner or @Abdul might 
have more understanding of SMM with which they can comment.

Thanks,
Tom

> 
> take care,
>    Gerd
> 


-=-=-=-=-=-=-=-=-=-=-=-
Groups.io Links: You receive all messages sent to this group.
View/Reply Online (#118340): https://edk2.groups.io/g/devel/message/118340
Mute This Topic: https://groups.io/mt/105593568/7686176
Group Owner: devel+owner@edk2.groups.io
Unsubscribe: https://edk2.groups.io/g/devel/unsub [rebecca@openfw.io]
-=-=-=-=-=-=-=-=-=-=-=-