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Message-ID: <d0f915ddd337ae3ce6ecb19f7d5f3faa6980b1de.camel@infradead.org>
Subject: Re: [PATCH] KVM: x86: ioapic: Fix level-triggered EOI and userspace
 IOAPIC reconfigure race
From:   David Woodhouse <dwmw2@infradead.org>
To:     Adamos Ttofari <attofari@amazon.de>, Thomas Huth <thuth@redhat.com>
Cc:     Sean Christopherson <seanjc@google.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>, x86@kernel.org,
        "H. Peter Anvin" <hpa@zytor.com>,
        Nikita Leshenko <nikita.leshchenko@oracle.com>,
        Liran Alon <liran.alon@oracle.com>,
        Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
        Radim =?UTF-8?Q?Kr=C4=8Dm=C3=A1=C5=99?= <rkrcmar@redhat.com>,
        kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Date:   Wed, 07 Dec 2022 09:42:15 +0000
In-Reply-To: <20221207091324.89619-1-attofari@amazon.de>
References: <20221207091324.89619-1-attofari@amazon.de>
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On Wed, 2022-12-07 at 09:13 +0000, Adamos Ttofari wrote:
> When split-irqchip is used KVM uses ioapic_handled_vectors to identify
> which vectors require an exit to userspace IOAPIC. Unfortunately, when th=
e
> IOAPIC is reconfigured while the interrupt is being handled, it will use
> the newest configuration; therefore, the EOI will not be delivered to
> IOAPIC.
>=20
> A previous commit 0fc5a36dd6b3
> ("KVM: x86: ioapic: Fix level-triggered EOI and IOAPIC reconfigure race")
> fixed the race for kernel ioapic, but the issue still persists for
> userspace IOAPIC:
>=20
> 1) Userspace IOAPIC sends a level triggered interrupt to VCPU0.
> 2) VCPU0's handler reconfigures the IOAPIC to route the interrupts to
>    VCPU1. (This can cause userspace IOAPIC to commit a new routing table,
>    eventually leading KVM to unset the vector in ioapic_handled_vectors)
> 3) VCPU0 triggers an EOI, and it's not delivered to userspace IOAPIC
>    because the vector bit is not set in ioapic_handled_vectors.
> 4) The loss of EOI, leaves remote_irr in IOAPIC set. Eventually blocking
>    new interrupts.
>=20
> To avoid the above scenario, we should apply a similar fix like
> commit 0fc5a36dd6b3 ("KVM: x86: ioapic: Fix level-triggered EOI and IOAPI=
C
> reconfigure race") Which is to add all pending and running vectors to
> ioapic_handled_vectors.
>=20
> Fixes: 0fc5a36dd6b3 ("KVM: x86: ioapic: Fix level-triggered EOI and IOAPI=
C reconfigure race")
>=20
> Signed-off-by: Adamos Ttofari <attofari@amazon.de>

Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>

Thanks.

This should fix https://gitlab.com/kvm-unit-tests/kvm-unit-tests/-/issues/1
shouldn't it?

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