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[34.83.136.168]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2cf1055cd5esm25047755ad.39.2026.07.16.12.50.53 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 16 Jul 2026 12:50:53 -0700 (PDT) Date: Thu, 16 Jul 2026 19:50:49 +0000 From: Samiullah Khawaja To: Lu Baolu Cc: Joerg Roedel , Will Deacon , Robin Murphy , Jason Gunthorpe , Kevin Tian , iommu@lists.linux.dev, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH 1/1] iommu/vt-d: Disallow SVA if page walk is not coherent Message-ID: References: <20260716053554.1642374-1-baolu.lu@linux.intel.com> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <20260716053554.1642374-1-baolu.lu@linux.intel.com> On Thu, Jul 16, 2026 at 01:35:53PM +0800, Lu Baolu wrote: >Hardware implementations report Scalable-Mode Page-walk Coherency Support >via the SMPWCS field in the extended capability register. If the hardware >does not support page-walk coherency, a clflush is required every time >the page table entries (which are walked by the IOMMU hardware) are >updated. > >In the SVA case, page tables are managed by the CPU mm core, not by the >IOMMU driver. Because the IOMMU driver has no way of knowing whether the >CPU page table management code has ensured coherency via clflush, the >driver must deny SVA if the hardware does not support coherent paging. > >Fixes: ff3dc6521f78 ("iommu/vt-d: Fix CPU and IOMMU SVM feature matching checks") >Cc: stable@vger.kernel.org >Signed-off-by: Lu Baolu >--- > drivers/iommu/intel/svm.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > >diff --git a/drivers/iommu/intel/svm.c b/drivers/iommu/intel/svm.c >index 0636987f03c8..432e35723ce9 100644 >--- a/drivers/iommu/intel/svm.c >+++ b/drivers/iommu/intel/svm.c >@@ -27,7 +27,7 @@ > > void intel_svm_check(struct intel_iommu *iommu) > { >- if (!pasid_supported(iommu)) >+ if (!pasid_supported(iommu) || !ecap_smpwc(iommu->ecap)) > return; > > if (cpu_feature_enabled(X86_FEATURE_GBPAGES) && >-- >2.43.0 > > Reviewed-by: Samiullah Khawaja Thanks, Sami