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

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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.


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