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

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Date: Tue, 16 Apr 2024 19:02:30 -0400
From: boris.ostrovsky@...cle.com
To: Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM/x86: Do not clear SIPI while in SMM



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@...cle.com> 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