[edk2-devel] [PATCH] UefiCpuPkg/CpuDxe: Fix boot error

[Ni, Ray]

> 
> [Guo] From my view point, it is not necessary to have these code for X64 since CS base
> address would always use 0 in long mode. But I will leave this to package owner
> to decide to remove it or not.
> For now to support AMD case, maybe we could check rax value to decide to use
> dword jump or qword jump. If high 4 bytes of rax is zero, dword jump will be used.
> With this, it has exact same behavior when CpuDxe driver is dispatch below 4GB.
> 
> >
> > If more time is needed to figure it out, though, it is probably best to
> > revert this in the mean time since I can't launch a VM (be it legacy or
> > SEV) on the latest tree.
> 
> [Guo] If we agree the above change to check rax, I could create a patch today.
> Let me know if having other comments.
> 

Tom,
We don't need to consider shadow stack because shadow stack is only enabled in SMM environment.

Guo,
I suggest we either revert the patch to keep the original 4G limitation, or use RETF to be maximum
compatible to Intel and AMD processors.
Checking high 4 bytes of RAX hides the problem in AMD processors.

Thanks,
Ray


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