linux-kernel - Re: [PATCH v3 2/2] KVM: x86/xen: Stop Xen timer before changing IRQ

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Message-ID: <c648744c096588d30771a22efa6d65c31fffd06c.camel@infradead.org>
Date:   Tue, 09 Aug 2022 10:22:17 +0100
From:   David Woodhouse <dwmw2@...radead.org>
To:     Coleman Dietsch <dietschc@....edu>, kvm@...r.kernel.org
Cc:     Sean Christopherson <seanjc@...gle.com>,
        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>, linux-kernel@...r.kernel.org,
        skhan@...uxfoundation.org, Pavel Skripkin <paskripkin@...il.com>,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        stable@...r.kernel.org,
        syzbot+e54f930ed78eb0f85281@...kaller.appspotmail.com
Subject: Re: [PATCH v3 2/2] KVM: x86/xen: Stop Xen timer before changing IRQ

On Mon, 2022-08-08 at 14:06 -0500, Coleman Dietsch wrote:
> Stop Xen timer (if it's running) prior to changing the IRQ vector and
> potentially (re)starting the timer. Changing the IRQ vector while the
> timer is still running can result in KVM injecting a garbage event, e.g.
> vm_xen_inject_timer_irqs() could see a non-zero xen.timer_pending from
> a previous timer but inject the new xen.timer_virq.

Hm, wasn't that already addressed in the first patch I saw, which just
called kvm_xen_stop_timer() unconditionally before (possibly) setting
it up again?

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