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Date: Tue, 16 Apr 2024 15:14:53 -0700
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Subject: Re: [PATCH] KVM/x86: Do not clear SIPI while in SMM
From: Sean Christopherson <seanjc@google.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: boris.ostrovsky@oracle.com, kvm@vger.kernel.org, 
	linux-kernel@vger.kernel.org
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On Wed, Apr 17, 2024, Paolo Bonzini wrote:
> On Tue, Apr 16, 2024 at 10:57=E2=80=AFPM <boris.ostrovsky@oracle.com> wro=
te:
> > 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 SIP=
I
> > is supposed to be dropped.
>=20
> 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)" exp=
licitly
says it's software's responsibility to detect whether or not the SIPI was d=
elivered,
and to resend SIPI(s) if needed.

  IPIs sent with this delivery mode are not automatically retried if the so=
urce
  APIC is unable to deliver it. It is up to the software to determine if th=
e
  SIPI was not successfully delivered and to reissue the SIPI if necessary.