linux-kernel - Re: [PATCH] iommu/vt-d: Wire up irq_ack() to irq_move

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Message-ID: <87ldsy15dx.ffs@tglx>
Date: Fri, 21 Mar 2025 21:43:38 +0100
From: Thomas Gleixner <tglx@...utronix.de>
To: Sean Christopherson <seanjc@...gle.com>, David Woodhouse
 <dwmw2@...radead.org>, Lu Baolu <baolu.lu@...ux.intel.com>, Joerg Roedel
 <joro@...tes.org>, Will Deacon <will@...nel.org>
Cc: iommu@...ts.linux.dev, linux-kernel@...r.kernel.org, Robert Lippert
 <rlippert@...gle.com>, Wentao Yang <wentaoyang@...gle.com>, Sean
 Christopherson <seanjc@...gle.com>
Subject: Re: [PATCH] iommu/vt-d: Wire up irq_ack() to irq_move_irq() for
 posted MSIs

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@...gle.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Reported-by: Wentao Yang <wentaoyang@...gle.com>
> Cc: stable@...r.kernel.org
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>

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