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Subject: Re: [edk2-devel] [PATCH v2] UefiCpuPkg/MpInitLib: Allocate a separate SEV-ES AP reset stack area
To: devel@edk2.groups.io, thomas.lendacky@amd.com
Cc: Brijesh Singh <brijesh.singh@amd.com>, Eric Dong <eric.dong@intel.com>,
 Ray Ni <ray.ni@intel.com>, Rahul Kumar <rahul1.kumar@intel.com>,
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From: "Laszlo Ersek" <lersek@redhat.com>
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Date: Wed, 19 May 2021 09:27:39 +0200
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On 05/17/21 17:03, Lendacky, Thomas wrote:
> On 5/16/21 11:22 PM, Laszlo Ersek wrote:

>> But now, with SEV-ES enabled, we'll have a separate, discontiguous area
>> -- and neither BackupAndPrepareWakeupBuffer(), nor its counterpart
>> RestoreWakeupBuffer() take that into account.
>>
>> Therefore I think, while this patch is regression-free for the SEV-ES
>> *disabled* case, it may corrupt memory (through not restoring the AP
>> stack area's original contents) with SEV-ES enabled.
> 
> This is the current behavior for SEV-ES. The wakeup buffer memory is
> marked as reserved, at least in the DXE phase.

Another question that occurred to me later: where does this reservation
happen? If we have a separate allocation for the AP stacks now, do we
need to reserve that too, separately?

What about PEI in general? Why is there no risk of corruption there?

(Sorry if these are lame questions!)

Thanks,
Laszlo