linux-kernel - Re: [PATCH v2] KVM: x86: ioapic: Fix level-triggered EOI and userspace I/OAPIC reconfigure race

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Date:   Fri, 9 Dec 2022 01:34:23 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Adamos Ttofari <attofari@...zon.de>
Cc:     dwmw@...zon.co.uk, Paolo Bonzini <pbonzini@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        Nikita Leshenko <nikita.leshchenko@...cle.com>,
        Liran Alon <liran.alon@...cle.com>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] KVM: x86: ioapic: Fix level-triggered EOI and
 userspace I/OAPIC reconfigure race

On Thu, Dec 08, 2022, Adamos Ttofari wrote:
> When scanning userspace I/OAPIC entries, intercept EOI for level-triggered
> IRQs if the current vCPU has a pending and/or in-service IRQ for the
> vector in its local API, even if the vCPU doesn't match the new entry's
> destination.  This fixes a race between userspace I/OAPIC reconfiguration
> and IRQ delivery that results in the vector's bit being left set in the
> remote IRR due to the eventual EOI not being forwarded to the userspace
> I/OAPIC.
> 
> Commit 0fc5a36dd6b3 ("KVM: x86: ioapic: Fix level-triggered EOI and IOAPIC
> reconfigure race") fixed the in-kernel IOAPIC, but not the userspace
> IOAPIC configuration, which has a similar race.
> 
> Fixes: 0fc5a36dd6b3 ("KVM: x86: ioapic: Fix level-triggered EOI and IOAPIC reconfigure race")
> 
> Signed-off-by: Adamos Ttofari <attofari@...zon.de>
> ---

Reviewed-by: Sean Christopherson <seanjc@...gle.com>