Re: [PATCH] KVM/x86: Do not clear SIPI while in SMM

[boris . ostrovsky]

On 4/16/24 6:14 PM, Sean Christopherson wrote:
> On Wed, Apr 17, 2024, Paolo Bonzini wrote:
> > On Tue, Apr 16, 2024 at 10:57 PM <boris.ostrovsky@xxxxxxxxxx> wrote:
> > > On 4/16/24 4:53 PM, Paolo Bonzini wrote:
> > > > On 4/16/24 22:47, Boris Ostrovsky wrote:
> > > > > Keeping the SIPI pending avoids this scenario.
> > > >
> > > > This is incorrect - it's yet another ugly legacy facet of x86, but we
> > > > have to live with it.  SIPI is discarded because the code is supposed
> > > > to retry it if needed ("INIT-SIPI-SIPI").
> > >
> > > I couldn't find in the SDM/APM a definitive statement about whether SIPI
> > > is supposed to be dropped.
> >
> > I think the manual is pretty consistent that SIPIs are never latched,
> > they're only ever used in wait-for-SIPI state.
>
> Ya, the "Interrupt Command Register (ICR)" section for "110 (Start-Up)" explicitly
> says it's software's responsibility to detect whether or not the SIPI was delivered,
> and to resend SIPI(s) if needed.
>
>    IPIs sent with this delivery mode are not automatically retried if the source
>    APIC is unable to deliver it. It is up to the software to determine if the
>    SIPI was not successfully delivered and to reissue the SIPI if necessary.


Right, I saw that. I was hoping to see something about SIPI being 
dropped. IOW my question was what happens to a SIPI that was delivered 
to a processor in SMM and not what should I do if it wasn't.

-boris