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iommu/arm-smmu-v3: Add update_safe bits to fix STE update sequence

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[ Upstream commit 2781f2a930 ]

C_BAD_STE was observed when updating nested STE from an S1-bypass mode to
an S1DSS-bypass mode. As both modes enabled S2, the used bit is slightly
different than the normal S1-bypass and S1DSS-bypass modes. As a result,
fields like MEV and EATS in S2's used list marked the word1 as a critical
word that requested a STE.V=0. This breaks a hitless update.

However, both MEV and EATS aren't critical in terms of STE update. One
controls the merge of the events and the other controls the ATS that is
managed by the driver at the same time via pci_enable_ats().

Add an arm_smmu_get_ste_update_safe() to allow STE update algorithm to
relax those fields, avoiding the STE update breakages.

After this change, entry_set has no caller checking its return value, so
change it to void.

Note that this change is required by both MEV and EATS fields, which were
introduced in different kernel versions. So add get_update_safe() first.
MEV and EATS will be added to arm_smmu_get_ste_update_safe() separately.

Fixes: 1e8be08d1c ("iommu/arm-smmu-v3: Support IOMMU_DOMAIN_NESTED")
Cc: stable@vger.kernel.org
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Shuai Xue <xueshuai@linux.alibaba.com>
Reviewed-by: Mostafa Saleh <smostafa@google.com>
Reviewed-by: Pranjal Shrivastava <praan@google.com>
Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Jason Gunthorpe 2026-01-15 10:23:28 -08:00 • committed by Sasha Levin
commit efd59553e4
3 changed files with 53 additions and 10 deletions
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