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Tue, 05 May 2026 09:11:27 -0700 (PDT) Received: from ziepe.ca ([213.147.98.98]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-48a824f9f0dsm393238945e9.15.2026.05.05.09.11.26 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 05 May 2026 09:11:27 -0700 (PDT) Received: from jgg by jggl with local (Exim 4.95) (envelope-from ) id 1wKIMo-000ALn-3b; Tue, 05 May 2026 13:11:26 -0300 Date: Tue, 5 May 2026 13:11:26 -0300 From: Jason Gunthorpe To: Pranjal Shrivastava Cc: Nicolin Chen , iommu@lists.linux.dev, Will Deacon , Joerg Roedel , Robin Murphy , Mostafa Saleh , Samiullah Khawaja , Daniel Mentz , Pasha Tatashin , David Matlack Subject: Re: [PATCH rc v2] iommu/arm-smmu-v3: Fix inconsistent ATS state tracking Message-ID: References: <20260504163842.2692314-1-praan@google.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: On Mon, May 04, 2026 at 07:33:07PM +0000, Pranjal Shrivastava wrote: > > > The issue was exposed under heavy load when running a VFIO-based DMA map > > > stress test: iova_stress [1] > > > > I wonder what's the real reason for pci_enable_ats() to fail: > > > > Yes, It's the dev->is_virtfn case (the one you suspect below) Oh.... This is a much larger problem then The VF should not fail to enable ATS, that is a meaningful bug, I'm not sure why are are just discovering this? It looks like the PF unconditionally calls pci_prepare_ats() during arm_smmu_probe_device(), so how does this happen: > > if (dev->is_virtfn) { > > pdev = pci_physfn(dev); > > if (pdev->ats_stu != ps) > > return -EINVAL; // maybe this one? ?? So, I think the right error handling for a case that shouldn't happen is to fail the attachment not to try to continue it broken? Jason