[PATCH 6.18 604/752] iommu/arm-smmu-v3: Do not set disable_ats unless vSTE is Translate

Sasha Levin
2026-02-28T17:56:55Z

From: Nicolin Chen <nicolinc@nvidia.com>

[ Upstream commit a45dd34663025c75652b27e384e91c9c05ba1d80 ]

A vSTE may have three configuration types: Abort, Bypass, and Translate.

An Abort vSTE wouldn't enable ATS, but the other two might.

It makes sense for a Transalte vSTE to rely on the guest vSTE.EATS field.

For a Bypass vSTE, it would end up with an S2-only physical STE, similar
to an attachment to a regular S2 domain. However, the nested case always
disables ATS following the Bypass vSTE, while the regular S2 case always
enables ATS so long as arm_smmu_ats_supported(master) == true.

Note that ATS is needed for certain VM centric workloads and historically
non-vSMMU cases have relied on this automatic enablement. So, having the
nested case behave differently causes problems.

To fix that, add a condition to disable_ats, so that it might enable ATS
for a Bypass vSTE, aligning with the regular S2 case.

Fixes: f27298a82ba0 ("iommu/arm-smmu-v3: Allow ATS for IOMMU_DOMAIN_NESTED")
Cc: stable@vger.kernel.org
Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
Reviewed-by: Pranjal Shrivastava <praan@google.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-iommufd.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-iommufd.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-iommufd.c
index 8cd8929bbfdf8..9ec5591565083 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-iommufd.c
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-iommufd.c
@@ -165,7 +165,9 @@ static int arm_smmu_attach_dev_nested(struct iommu_domain *domain,
* config bit here base this off the EATS value in the STE. If the EATS
* is set then the VM must generate ATC flushes.
*/
- state.disable_ats = !nested_domain->enable_ats;
+ if (FIELD_GET(STRTAB_STE_0_CFG, le64_to_cpu(nested_domain->ste[0])) ==
+ STRTAB_STE_0_CFG_S1_TRANS)
+ state.disable_ats = !nested_domain->enable_ats;
ret = arm_smmu_attach_prepare(&state, domain);
if (ret) {
mutex_unlock(&arm_smmu_asid_lock);
--
2.51.0