Re: [edk2-devel] [PATCH 1/1] UefiCpuPkg/MpInitLib: fix apic mode for cpu hotplug

["Ni, Ray" <ray.ni@intel.com>]

Thanks for confirming that.

> -----Original Message-----
> From: devel@edk2.groups.io <devel@edk2.groups.io> On Behalf Of Gerd
> Hoffmann
> Sent: Tuesday, March 21, 2023 7:54 PM
> To: Ni, Ray <ray.ni@intel.com>
> Cc: devel@edk2.groups.io; Pawel Polawski <ppolawsk@redhat.com>; Kumar,
> Rahul R <rahul.r.kumar@intel.com>; Oliver Steffen <osteffen@redhat.com>;
> Dong, Eric <eric.dong@intel.com>
> Subject: Re: [edk2-devel] [PATCH 1/1] UefiCpuPkg/MpInitLib: fix apic mode
> for cpu hotplug
> 
> On Tue, Mar 21, 2023 at 07:28:44AM +0000, Ni, Ray wrote:
> > > +  } else if ((PcdGet32 (PcdCpuBootLogicalProcessorNumber) > 0) &&
> > > +             (PcdGet32 (PcdCpuMaxLogicalProcessorNumber) > 255))
> > > +  {
> > > +    X2Apic = TRUE;
> >
> > Gerd,
> > I agree with your needs that want X2 APIC even the actual processor
> number in BIOS phase <= 255.
> >
> > Question: Is it possible that BIOS stays at XAPIC, and later OS switches to X2
> APIC when the maximum CPU count > 255?
> 
> Linux doesn't do that.  In case x2apic mode is not active at boot the
> number of CPUs will be limited to 255.
> 
> > I am thinking about adding a new PCD to tell MP code switch to x2 apic
> > in the first time AP wakes up. Possible timeline for the code change
> > is about within 1 month. Do you think it can meet your needs?
> 
> So the idea being that OVMF simply sets that PCD if needed (probably at
> the same place where PcdCpuMaxLogicalProcessorNumber is set)?  That
> would work too.
> 
> take care,
>   Gerd
> 
> 
> 
> 
>