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Subject[PATCH 5.3 284/344] iommu/arm-smmu-v3: Disable detection of ATS and PRI
From: Will Deacon <>

commit b5e86196b83fd68e065a7c811ab8925fb0dc3893 upstream.

Detecting the ATS capability of the SMMU at probe time introduces a
spinlock into the ->unmap() fast path, even when ATS is not actually
in use. Furthermore, the ATC invalidation that exists is broken, as it
occurs before invalidation of the main SMMU TLB which leaves a window
where the ATC can be repopulated with stale entries.

Given that ATS is both a new feature and a specialist sport, disable it
for now whilst we fix it properly in subsequent patches. Since PRI
requires ATS, disable that too.

Cc: <>
Fixes: 9ce27afc0830 ("iommu/arm-smmu-v3: Add support for PCI ATS")
Acked-by: Robin Murphy <>
Signed-off-by: Will Deacon <>
Signed-off-by: Greg Kroah-Hartman <>

drivers/iommu/arm-smmu-v3.c | 2 ++
1 file changed, 2 insertions(+)

--- a/drivers/iommu/arm-smmu-v3.c
+++ b/drivers/iommu/arm-smmu-v3.c
@@ -2843,11 +2843,13 @@ static int arm_smmu_device_hw_probe(stru

/* Boolean feature flags */
+#if 0 /* ATS invalidation is slow and broken */
smmu->features |= ARM_SMMU_FEAT_PRI;

smmu->features |= ARM_SMMU_FEAT_ATS;

if (reg & IDR0_SEV)
smmu->features |= ARM_SMMU_FEAT_SEV;

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