From: Marc Zyngier <maz@kernel•org>
To: Oliver Upton <oupton@kernel•org>
Cc: Hyunwoo Kim <imv4bel@gmail•com>,
joey.gouly@arm•com, seiden@linux•ibm.com, suzuki.poulose@arm•com,
yuzenghui@huawei•com, catalin.marinas@arm•com, will@kernel•org,
Sascha.Bischoff@arm•com, jic23@kernel•org,
linux-arm-kernel@lists•infradead.org, kvmarm@lists•linux.dev
Subject: Re: [PATCH] KVM: arm64: vgic: Use list_del_rcu() when flushing pending LPIs
Date: Fri, 05 Jun 2026 09:17:56 +0100 [thread overview]
Message-ID: <87a4t99z9n.wl-maz@kernel.org> (raw)
In-Reply-To: <aiJi5a3JJ-TbWL-s@kernel.org>
On Fri, 05 Jun 2026 06:47:17 +0100,
Oliver Upton <oupton@kernel•org> wrote:
>
> Hi Hyunwoo,
>
> On Fri, Jun 05, 2026 at 06:16:08AM +0900, Hyunwoo Kim wrote:
> > vgic_v3_fold_lr_state() walks the ap_list from last_lr_irq without holding
> > the ap_list_lock, relying on vgic_irq being freed via kfree_rcu() and on
> > interrupts being disabled. vgic_flush_pending_lpis() removes entries with
> > list_del(), which clobbers a node's next pointer, so when another vCPU
> > disables LPIs via GICR_CTLR the walk can follow the clobbered next pointer
> > from a removed node, or from the node that last_lr_irq points to.
> >
> > Remove entries with list_del_rcu() so that the next pointer stays valid
> > until the walk completes.
> >
> > Fixes: 3cfd59f81e0f ("KVM: arm64: GICv3: Handle LR overflow when EOImode==0")
> > Signed-off-by: Hyunwoo Kim <imv4bel@gmail•com>
>
> Changing only one of the writer paths to use the rculist helpers does
> not make the ap_list an rculist. Insertions are not RCU-safe, nor are
> deleations from vgic_prune_ap_list().
>
> And TBH, the real bug here is the fact that vgic_v3_fold_lr_state() isn't
> taking the ap_list_lock.
Yup, that'd be more sensible. I need to convince myself that there is
no possible path from vgic_v*_fold_lr() to vgic_irq_queue_unlock(),
because that one does actually acquire that lock.
M.
--
Jazz isn't dead. It just smells funny.
prev parent reply other threads:[~2026-06-05 8:14 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-06-04 21:16 [PATCH] KVM: arm64: vgic: Use list_del_rcu() when flushing pending LPIs Hyunwoo Kim
2026-06-05 5:47 ` Oliver Upton
2026-06-05 8:17 ` Marc Zyngier [this message]
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