Re: [edk2-devel] [PATCH 03/16] MdePkg/BaseLib: Add a new VMGEXIT instruction invocation for SVSM

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

On 1/30/24 05:51, Gerd Hoffmann wrote:
> On Mon, Jan 29, 2024 at 09:51:47AM -0600, Tom Lendacky wrote:
>> On 1/29/24 07:22, Gerd Hoffmann wrote:
>>>> +global ASM_PFX(AsmVmgExitSvsm)
>>>> +ASM_PFX(AsmVmgExitSvsm):
>>>> +;
>>>> +; NASM doesn't support the vmmcall instruction in 32-bit mode and NASM versions
>>>> +; before 2.12 cannot translate the 64-bit "rep vmmcall" instruction into elf32
>>>> +; format. Given that VMGEXIT does not make sense on IA32, provide a stub
>>>> +; implementation that is identical to CpuBreakpoint(). In practice,
>>>> +; AsmVmgExitSvsm() should never be called on IA32.
>>>> +;
>>>> +    int  3
>>>> +    ret
>>>
>>> Why?  I assume because the calling convention is only defined for X64?
>>>
>>> Why do we need this in the first place if this is never called on IA32?
>>>
>>> Wouldn't it be better to have an ASSERT(FALSE) for IA32 in the code
>>> calling this?
>>
>> An ASSERT() only works for DEBUG code.
>>
>> I was following in the steps of AsmVmgExit, where we did this. I suppose we
>> could just not have it at all for IA32 and cause a build failure if someone
>> was to try and call this from 32-bit code. Thoughts?
> 
> See also patch #13 sub-thread.  Maybe just move the 32-bit build to the
> Null versions of the Libraries.
> 
> SEV-SNP + SVSM apparently is 64-bit only already (there is no 32-bit
> calling convention).
> 
> Over the last year Intel landed full 64-bit PEI support in edk2, which
> means the pure 64-bit build (OvmfPkgX64.dsc) has feature parity with
> the 32-bit PEI / 64-bit DXE build (OvmfPkgIa32X64.dsc).
> 
> So maybe we can simply leave 32-bit support behind and remove SEV
> support from OvmfPkgIa32X64.dsc and OvmfPkgIa32.dsc builds ...

That would break anyone that is currently using OvmfPkgIa32X64.dsc for 
base SEV (not ES or SNP), but I'm not sure if that is a real concern. For 
OvmfPkgIa32.dsc, no version of SEV will work, so that is doable.

Can we look at doing that cleanup after this series?

Thanks,
Tom

> 
> take care,
>    Gerd
> 


-=-=-=-=-=-=-=-=-=-=-=-
Groups.io Links: You receive all messages sent to this group.
View/Reply Online (#114913): https://edk2.groups.io/g/devel/message/114913
Mute This Topic: https://groups.io/mt/103986440/7686176
Group Owner: devel+owner@edk2.groups.io
Unsubscribe: https://edk2.groups.io/g/devel/unsub [rebecca@openfw.io]
-=-=-=-=-=-=-=-=-=-=-=-