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[35.187.245.222]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-81fa10c5502sm11275223b3a.24.2026.01.19.23.25.34 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 19 Jan 2026 23:25:36 -0800 (PST) Date: Tue, 20 Jan 2026 07:25:31 +0000 From: Pranjal Shrivastava To: Nicolin Chen Cc: will@kernel.org, jgg@nvidia.com, robin.murphy@arm.com, joro@8bytes.org, linux-arm-kernel@lists.infradead.org, iommu@lists.linux.dev, linux-kernel@vger.kernel.org Subject: Re: [PATCH rc] iommu/arm-smmu-v3: Do not set disable_ats unless vSTE is Translate Message-ID: References: <20260115011243.1302402-1-nicolinc@nvidia.com> Precedence: bulk X-Mailing-List: iommu@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260115011243.1302402-1-nicolinc@nvidia.com> On Wed, Jan 14, 2026 at 05:12:43PM -0800, Nicolin Chen wrote: > 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 > --- > 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); This makes sense. The nested_domain->enable_ats should indeed only be checked for Translate configs. Reviewed-by: Pranjal Shrivastava Thanks, Praan