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

["Ni, Ruiyu" <ruiyu.ni@intel.com>]

Thanks/Ray

> -----Original Message-----
> From: edk2-devel <edk2-devel-bounces@lists.01.org> On Behalf Of Paolo
> Bonzini
> Sent: Thursday, June 14, 2018 4:52 AM
> To: Laszlo Ersek <lersek@redhat.com>; Leo Duran <leo.duran@amd.com>;
> edk2-devel@lists.01.org
> Cc: Justen, Jordan L <jordan.l.justen@intel.com>; Brijesh Singh
> <brijesh.singh@amd.com>; Jeff Fan <jeff.fan@intel.com>; Gao, Liming
> <liming.gao@intel.com>
> Subject: Re: [edk2] [PATCH] UefiCpuPkg/LocalApicLib: Exclude second
> SendIpi sequence on AMD processors.
> 
> 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).

Why the recent processors don't need INIT-SIPI-SIPI?
I thought it is the only way to wake up processors when it's halted (HLT).

> 
> Paolo
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