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Thu, 23 Apr 2026 03:09:36 -0700 (PDT) From: avinash pal To: David Woodhouse Cc: Lu Baolu , Joerg Roedel , Will Deacon , Robin Murphy , avinash pal , iommu@lists.linux.dev, linux-kernel@vger.kernel.org, stable@vger.kernel.org, Giovanni Pancotti Subject: [PATCH stable 6.12 1/2] iommu/vt-d: fail map loudly on stale DMA PTE Date: Thu, 23 Apr 2026 15:39:03 +0530 Message-ID: <20260423100904.5966-2-avinashpal441@gmail.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260423100904.5966-1-avinashpal441@gmail.com> References: <20260423100904.5966-1-avinashpal441@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit In __domain_mapping(), when dma_pte_present(pte) is true the existing WARN continues execution, leaving the domain in an inconsistent state: a new PTE is silently installed on top of a live one. Replace it with: - pr_err_ratelimited: prints conflicting vPFN + old PTE value - WARN_ON_ONCE: one-shot kernel warning with stack trace - return -EEXIST: abort the bad map; no silent corruption The root cause is in the unmap path — see the companion dma-iommu.c fix. Reported-by: Giovanni Pancotti Link: https://bugzilla.kernel.org/show_bug.cgi?id=221389 Cc: stable@vger.kernel.org Signed-off-by: avinash pal --- drivers/iommu/intel/iommu.c | 50 ++++++++++++++++++++++++++++--------- 1 file changed, 38 insertions(+), 12 deletions(-) diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c index c799cc67d..4a8937b44 100644 --- a/drivers/iommu/intel/iommu.c +++ b/drivers/iommu/intel/iommu.c @@ -1777,14 +1777,25 @@ static void switch_to_super_page(struct dmar_domain *domain, pte = pfn_to_dma_pte(domain, start_pfn, &level, GFP_ATOMIC); - if (dma_pte_present(pte)) { - dma_pte_free_pagetable(domain, start_pfn, - start_pfn + lvl_pages - 1, - level + 1); - - cache_tag_flush_range(domain, start_pfn << VTD_PAGE_SHIFT, - end_pfn << VTD_PAGE_SHIFT, 0); - } + if (dma_pte_present(pte)) { + /* + * A live DMA PTE is already installed at this vPFN. + * This violates the map/unmap contract: an IOVA must be + * fully unmapped and the IOTLB drained before reuse. + * + * Root cause: missing iommu_iotlb_sync() before + * free_iova_fast() in __iommu_dma_unmap_sg() on the + * lazy-flush path. The companion patch in dma-iommu.c + * fixes that; this guard makes the violation explicit. + */ + pr_err_ratelimited( + "DMAR: stale PTE at vPFN 0x%lx (val=0x%016llx) " + "-- IOVA reused before IOTLB drain +", + iov_pfn, (unsigned long long)pte->val); + WARN_ON_ONCE(1); + return -EEXIST; + } pte++; start_pfn += lvl_pages; @@ -3663,10 +3674,25 @@ int prepare_domain_attach_device(struct iommu_domain *domain, struct dma_pte *pte; pte = dmar_domain->pgd; - if (dma_pte_present(pte)) { - dmar_domain->pgd = phys_to_virt(dma_pte_addr(pte)); - iommu_free_page(pte); - } + if (dma_pte_present(pte)) { + /* + * A live DMA PTE is already installed at this vPFN. + * This violates the map/unmap contract: an IOVA must be + * fully unmapped and the IOTLB drained before reuse. + * + * Root cause: missing iommu_iotlb_sync() before + * free_iova_fast() in __iommu_dma_unmap_sg() on the + * lazy-flush path. The companion patch in dma-iommu.c + * fixes that; this guard makes the violation explicit. + */ + pr_err_ratelimited( + "DMAR: stale PTE at vPFN 0x%lx (val=0x%016llx) " + "-- IOVA reused before IOTLB drain +", + iov_pfn, (unsigned long long)pte->val); + WARN_ON_ONCE(1); + return -EEXIST; + } dmar_domain->agaw--; } -- 2.53.0