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From: Thomas Gleixner <tglx@linutronix.de>
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To: Sean Christopherson <seanjc@google.com>, David Woodhouse
 <dwmw2@infradead.org>, Lu Baolu <baolu.lu@linux.intel.com>, Joerg Roedel
 <joro@8bytes.org>, Will Deacon <will@kernel.org>
Cc: iommu@lists.linux.dev, linux-kernel@vger.kernel.org, Robert Lippert
 <rlippert@google.com>, Wentao Yang <wentaoyang@google.com>, Sean
 Christopherson <seanjc@google.com>
Subject: Re: [PATCH] iommu/vt-d: Wire up irq_ack() to irq_move_irq() for
 posted MSIs
In-Reply-To: <20250321194249.1217961-1-seanjc@google.com>
References: <20250321194249.1217961-1-seanjc@google.com>
Date: Fri, 21 Mar 2025 21:43:38 +0100
Message-ID: <87ldsy15dx.ffs@tglx>
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On Fri, Mar 21 2025 at 12:42, Sean Christopherson wrote:
> Set the posted MSI irq_chip's irq_ack() hook to irq_move_irq() instead of
> a dummy/empty callback so that posted MSIs process pending changes to the
> IRQ's SMP affinity.  Failure to honor a pending set-affinity results in
> userspace being unable to change the effective affinity of the IRQ, as
> IRQD_SETAFFINITY_PENDING is never cleared and so irq_set_affinity_locked()
> always defers moving the IRQ.
>
> The issue is most easily reproducible by setting /proc/irq/xx/smp_affinity
> multiple times in quick succession, as only the first update is likely to
> be handled in process context.
>
> Fixes: ed1e48ea4370 ("iommu/vt-d: Enable posted mode for device MSIs")
> Cc: Robert Lippert <rlippert@google.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Reported-by: Wentao Yang <wentaoyang@google.com>
> Cc: stable@vger.kernel.org
> Signed-off-by: Sean Christopherson <seanjc@google.com>

Reviewed-by: Thomas Gleixner <tglx@linutronix.de>