linux-kernel - [PATCH] irqchip/gic-v4: Fix ordering between vmapp and vpe locks

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Message-Id: <20240723175203.3193882-1-maz@kernel.org>
Date: Tue, 23 Jul 2024 18:52:03 +0100
From: Marc Zyngier <maz@...nel.org>
To: linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Cc: Thomas Gleixner <tglx@...utronix.de>,
	Zhou Wang <wangzhou1@...ilicon.com>
Subject: [PATCH] irqchip/gic-v4: Fix ordering between vmapp and vpe locks

The (recently established) lock ordering mandates that the per-VM
vmapp_lock is acquired before we take the per-VPE lock.

As it turns out, its_vpe_set_affinity() takes the VPE lock, and
then calls into its_send_vmovp(), which itself takes the vmapp
lock. Obviously, this isn't what we want.

As its_send_vmovp() is only called from its_vpe_set_affinity(),
hoist the vmapp locking from the former into the latter, restoring
the expected order.

Fixes: f0eb154c39471 ("irqchip/gic-v4: Substitute vmovp_lock for a per-VM lock")
Reported-by: Zhou Wang <wangzhou1@...ilicon.com>
Signed-off-by: Marc Zyngier <maz@...nel.org>
---
 drivers/irqchip/irq-gic-v3-its.c | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
index 951ec140bcea2..b88c6011c8771 100644
--- a/drivers/irqchip/irq-gic-v3-its.c
+++ b/drivers/irqchip/irq-gic-v3-its.c
@@ -1328,12 +1328,6 @@ static void its_send_vmovp(struct its_vpe *vpe)
 		return;
 	}
 
-	/*
-	 * Protect against concurrent updates of the mapping state on
-	 * individual VMs.
-	 */
-	guard(raw_spinlock_irqsave)(&vpe->its_vm->vmapp_lock);
-
 	/*
 	 * Yet another marvel of the architecture. If using the
 	 * its_list "feature", we need to make sure that all ITSs
@@ -3808,7 +3802,7 @@ static int its_vpe_set_affinity(struct irq_data *d,
 	struct its_vpe *vpe = irq_data_get_irq_chip_data(d);
 	unsigned int from, cpu = nr_cpu_ids;
 	struct cpumask *table_mask;
-	unsigned long flags;
+	unsigned long flags, vmapp_flags;
 
 	/*
 	 * Changing affinity is mega expensive, so let's be as lazy as
@@ -3822,7 +3816,14 @@ static int its_vpe_set_affinity(struct irq_data *d,
 	 * protect us, and that we must ensure nobody samples vpe->col_idx
 	 * during the update, hence the lock below which must also be
 	 * taken on any vLPI handling path that evaluates vpe->col_idx.
+	 *
+	 * Finally, we must protect ourselves against concurrent
+	 * updates of the mapping state on this VM should the ITS list
+	 * be in use.
 	 */
+	if (its_list_map)
+		raw_spin_lock_irqsave(&vpe->its_vm->vmapp_lock, vmapp_flags);
+
 	from = vpe_to_cpuid_lock(vpe, &flags);
 	table_mask = gic_data_rdist_cpu(from)->vpe_table_mask;
 
@@ -3852,6 +3853,9 @@ static int its_vpe_set_affinity(struct irq_data *d,
 	irq_data_update_effective_affinity(d, cpumask_of(cpu));
 	vpe_to_cpuid_unlock(vpe, flags);
 
+	if (its_list_map)
+		raw_spin_unlock_irqrestore(&vpe->its_vm->vmapp_lock, vmapp_flags);
+
 	return IRQ_SET_MASK_OK_DONE;
 }
 
-- 
2.39.2