linux-kernel - [PATCH 5.2 258/313] iommu/arm-smmu-v3: Disable detection of ATS and PRI

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Message-Id: <20191003154558.449042558@linuxfoundation.org>
Date:   Thu,  3 Oct 2019 17:53:56 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Robin Murphy <robin.murphy@....com>,
        Will Deacon <will@...nel.org>
Subject: [PATCH 5.2 258/313] iommu/arm-smmu-v3: Disable detection of ATS and PRI

From: Will Deacon <will@...nel.org>

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: <stable@...r.kernel.org>
Fixes: 9ce27afc0830 ("iommu/arm-smmu-v3: Add support for PCI ATS")
Acked-by: Robin Murphy <robin.murphy@....com>
Signed-off-by: Will Deacon <will@...nel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 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
@@ -2817,11 +2817,13 @@ static int arm_smmu_device_hw_probe(stru
 	}
 
 	/* Boolean feature flags */
+#if 0	/* ATS invalidation is slow and broken */
 	if (IS_ENABLED(CONFIG_PCI_PRI) && reg & IDR0_PRI)
 		smmu->features |= ARM_SMMU_FEAT_PRI;
 
 	if (IS_ENABLED(CONFIG_PCI_ATS) && reg & IDR0_ATS)
 		smmu->features |= ARM_SMMU_FEAT_ATS;
+#endif
 
 	if (reg & IDR0_SEV)
 		smmu->features |= ARM_SMMU_FEAT_SEV;