linux-kernel - [PATCH rc] iommu/arm-smmu-v3: Fix smmu_domain->nr_ats

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Message-ID: <20250801030127.2006979-1-nicolinc@nvidia.com>
Date: Thu, 31 Jul 2025 20:01:27 -0700
From: Nicolin Chen <nicolinc@...dia.com>
To: <jgg@...dia.com>, <will@...nel.org>
CC: <joro@...tes.org>, <robin.murphy@....com>,
	<linux-arm-kernel@...ts.infradead.org>, <iommu@...ts.linux.dev>,
	<linux-kernel@...r.kernel.org>
Subject: [PATCH rc] iommu/arm-smmu-v3: Fix smmu_domain->nr_ats_masters decrement

The arm_smmu_attach_commit() updates master->ats_enabled before calling
arm_smmu_remove_master_domain() that is supposed to clean up everything
in the old domain, including the old domain's nr_ats_masters. So, it is
supposed to use the old ats_enabled state of the device, not an updated
state.

This isn't a problem if switching between two domains where:
 - old ats_enabled = false; new ats_enabled = false
 - old ats_enabled = true;  new ats_enabled = true
but can fail cases where:
 - old ats_enabled = false; new ats_enabled = true
   (old domain should keep the counter but incorrectly decreased it)
 - old ats_enabled = true;  new ats_enabled = false
   (old domain needed to decrease the counter but incorrectly missed it)

Update master->ats_enabled after arm_smmu_remove_master_domain() to fix
this.

Fixes: 7497f4211f4f ("iommu/arm-smmu-v3: Make changing domains be hitless for ATS")
Cc: stable@...r.kernel.org
Signed-off-by: Nicolin Chen <nicolinc@...dia.com>
---
 drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
index 312bc31d7e8eb..3c81139faecae 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
@@ -2997,9 +2997,9 @@ void arm_smmu_attach_commit(struct arm_smmu_attach_state *state)
 		/* ATS is being switched off, invalidate the entire ATC */
 		arm_smmu_atc_inv_master(master, IOMMU_NO_PASID);
 	}
-	master->ats_enabled = state->ats_enabled;
 
 	arm_smmu_remove_master_domain(master, state->old_domain, state->ssid);
+	master->ats_enabled = state->ats_enabled;
 }
 
 static int arm_smmu_attach_dev(struct iommu_domain *domain, struct device *dev)
-- 
2.43.0