Re: [PATCH] UefiCpuPkg/LocalApicLib: Exclude second SendIpi sequence on AMD processors.

[Paolo Bonzini <pbonzini@redhat.com>]

On 13/06/2018 22:49, Laszlo Ersek wrote:
> Hello Leo,
> 
> On 06/13/18 22:11, Leo Duran wrote:
>> On AMD processors the second SendIpi in the SendInitSipiSipi and
>> SendInitSipiSipiAllExcludingSelf routines is not required, and may cause
>> undesired side-effects during MP initialization.
>>
>> This patch leverages the StandardSignatureIsAuthenticAMD check to exclude
>> the second SendIpi and its associated MicroSecondDelay (200).
> 
> QEMU and KVM emulate some AMD processors too; of particular interest is
> the recent EPYC addition, I believe (for SME/SEV, minimally).
> 
> Did you check whether the StandardSignatureIsAuthenticAMD() check
> applies to those QEMU VCPU models, and if so, whether omitting the
> second Startup IPI interferes with *V*CPU startup in OVMF guests? (In
> multiprocessing modules, such as CpuMpPei, CpuDxe, and PiSmmCpuDxeSmm.)
> 
> Adding Brijesh, Paolo and Igor.

Actually I would be surprised if any recent processor needs the
INIT-SIPI-SIPI (though I'm not sure what undesired side effects it might
trigger).

Paolo