From a45dd34663025c75652b27e384e91c9c05ba1d80 Mon Sep 17 00:00:00 2001 From: Nicolin Chen Date: Wed, 14 Jan 2026 17:12:43 -0800 Subject: [PATCH] iommu/arm-smmu-v3: Do not set disable_ats unless vSTE is Translate 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 Signed-off-by: Nicolin Chen Reviewed-by: Pranjal Shrivastava Reviewed-by: Jason Gunthorpe Signed-off-by: Will Deacon --- 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 93fdadd07431a..823461a26659f 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); -- 2.47.3