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

[Nicolin Chen <nicolinc@nvidia.com>]

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>
---
 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 93fdadd07431..823461a26659 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
@@ -177,7 +177,9 @@ 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);
-- 
2.43.0