linux-kernel - Re: [PATCH 4/7] KVM: x86: SVM: fix avic_kick_target_vcpus

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Message-ID: <c7fb78e2-2650-f9a2-3062-5d5ecc34332b@redhat.com>
Date:   Wed, 8 Jun 2022 15:21:42 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Maxim Levitsky <mlevitsk@...hat.com>, kvm@...r.kernel.org
Cc:     Wanpeng Li <wanpengli@...cent.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Jim Mattson <jmattson@...gle.com>,
        "H. Peter Anvin" <hpa@...or.com>, Joerg Roedel <joro@...tes.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>,
        Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
        linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        x86@...nel.org, Borislav Petkov <bp@...en8.de>,
        stable@...r.kernel.org
Subject: Re: [PATCH 4/7] KVM: x86: SVM: fix avic_kick_target_vcpus_fast

On 6/6/22 20:08, Maxim Levitsky wrote:
> There are two issues in avic_kick_target_vcpus_fast
> 
> 1. It is legal to issue an IPI request with APIC_DEST_NOSHORT
>     and a physical destination of 0xFF (or 0xFFFFFFFF in case of x2apic),
>     which must be treated as a broadcast destination.
> 
>     Fix this by explicitly checking for it.
>     Also don’t use ‘index’ in this case as it gives no new information.
> 
> 2. It is legal to issue a logical IPI request to more than one target.
>     Index field only provides index in physical id table of first
>     such target and therefore can't be used before we are sure
>     that only a single target was addressed.
> 
>     Instead, parse the ICRL/ICRH, double check that a unicast interrupt
>     was requested, and use that info to figure out the physical id
>     of the target vCPU.
>     At that point there is no need to use the index field as well.
> 
> 
> In addition to fixing the above	issues,	also skip the call to
> kvm_apic_match_dest.
> 
> It is possible to do this now, because now as long as AVIC is not
> inhibited, it is guaranteed that none of the vCPUs changed their
> apic id from its default value.
> 
> 
> This fixes boot of windows guest with AVIC enabled because it uses
> IPI with 0xFF destination and no destination shorthand.
> 
> Fixes: 7223fd2d5338 ("KVM: SVM: Use target APIC ID to complete AVIC IRQs when possible")
> Cc: stable@...r.kernel.org
> 
> Signed-off-by: Maxim Levitsky <mlevitsk@...hat.com>

Is it possible to use kvm_intr_is_single_vcpu_fast, or am I missing 
something?

Series queued, thanks.

Paolo