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[159.2.239.150]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-53032ff4e90sm17442101cf.2.2026.09.02.05.08.33 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 02 Sep 2026 05:08:33 -0700 (PDT) Received: from jgg by wakko with local (Exim 4.97) (envelope-from ) id 1x1jlY-0000000E9vh-1aE2; Wed, 02 Sep 2026 09:08:32 -0300 Date: Wed, 2 Sep 2026 09:08:32 -0300 From: Jason Gunthorpe To: David Hu Cc: sumit.semwal@linaro.org, christian.koenig@amd.com, alex@shazbot.org, ankita@nvidia.com, chriscli@google.com, david.laight.linux@gmail.com, dri-devel@lists.freedesktop.org, iommu@lists.linux.dev, jmoroni@google.com, kevin.tian@intel.com, kpberry@google.com, leon@kernel.org, linaro-mm-sig@lists.linaro.org, linux-kernel@vger.kernel.org, linux-media@vger.kernel.org, nicolinc@nvidia.com, praan@google.com, sashiko-bot@kernel.org, stable@vger.kernel.org, viursachi@google.com, xuehaohu@google.com, Leon Romanovsky Subject: Re: [PATCH v8 2/2] dma-buf: Split sgl by largest page-aligned chunk Message-ID: <20260902120832.GB2890729@ziepe.ca> References: <20260901170849.4052816-1-dhu@x6u.co> <20260901170849.4052816-3-dhu@x6u.co> Precedence: bulk X-Mailing-List: linux-media@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260901170849.4052816-3-dhu@x6u.co> On Tue, Sep 01, 2026 at 05:08:49PM +0000, David Hu wrote: > From: David Hu > > Currently, `fill_sg_entry()` splits the scatterlist using `UINT_MAX`. > This creates a non-page-aligned DMA length (`0xFFFFFFFF`) for the > first entry, resulting in non-page-aligned DMA addresses for all > subsequent entries. This patch is fine, but pedenatically a scatterlist's entry limit should be bounded to dma_get_max_seg_size(), though I don't think it helps this. Operating scatterlists at the size limits has proven problematic in a number of places already... > In addition, a non-page-aligned sgl length will trigger an edge case > in `ib_umem_find_best_pgsz()`. In case of a discontinuity in later > buffers, we will have a `va` with lowest bit set to 1. That will lead > to `ib_umem_find_best_pgsz()` always return 0, and break the promise > to find best page size for the mapping on the NIC side. That's an IB side bug, the newer logic that joins adjacent SGLs should have avoided it? Jason