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[2a02:3100:b1a4:1201:5c78:89f4:99d8:70d7]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4a35a04ad39sm473163315e9.1.2026.10.26.01.03.24 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 26 Oct 2026 01:03:25 -0700 (PDT) Date: Mon, 26 Oct 2026 09:03:22 +0100 From: Karl Mehltretter To: Alistair Popple Cc: dri-devel@lists.freedesktop.org, christian.koenig@amd.com, sumit.semwal@linaro.org, jgg@nvidia.com, Thomas =?utf-8?Q?Hellstr=C3=B6m?= , Simona Vetter , Matthew Brost , Vivek Kasireddy , Dongwon Kim , Leon Romanovsky , Kevin Tian , Xu Yilun , Baolu Lu , Felix Kuehling , Alex Deucher , intel-xe@lists.freedesktop.org, amd-gfx@lists.freedesktop.org, linux-media@vger.kernel.org, linaro-mm-sig@lists.linaro.org, linux-rdma@vger.kernel.org, iommu@lists.linux.dev, Alexey Kardashevskiy , zhipingz@meta.com, treding@nvidia.com, jhubbard@nvidia.com Subject: Re: [PATCH 05/26] dma-buf: Let the exporter select mapping type at pin/map Message-ID: References: <20261026053623.202642-1-apopple@nvidia.com> <20261026053623.202642-6-apopple@nvidia.com> X-Mailing-List: iommu@lists.linux.dev List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261026053623.202642-6-apopple@nvidia.com> On Mon, Oct 26, 2026 at 04:35:56PM +0100, Alistair Popple wrote: > +struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *attach, > + enum dma_data_direction direction) > +{ > + struct sg_table *sg_table; > + int ret; > + > + might_sleep(); > + > + if (WARN_ON(!attach || !attach->dmabuf)) > + return ERR_PTR(-EINVAL); > + > + dma_resv_assert_held(attach->dmabuf->resv); > + > + ret = dma_buf_mapping_select(attach); > + if (ret) > + return ERR_PTR(ret); > + > + sg_table = __dma_buf_sgt_map_attachment(attach, direction); > + if (IS_ERR(sg_table)) > + /* Nothing was established, so the choice may be made afresh */ > + attach->selected = false; > + > + return sg_table; > +} The map-failure report from Sashiko [1] reproduces with a KUnit test against the full series: pin selects B -> map returns -EIO -> selected is cleared -> retry selects A, with the original pin still held The exporter pin count stays at 1. Preserving selected when it was true on entry makes the test pass. Patch 7 needs the same fix. Could dma_buf_mapping_select() report whether it made a new selection? Then the error path could undo only that choice, without dropping one established by an earlier pin or map. On the Sashiko failed-pin report: ("Because the attachment is not pinned, the exporter may migrate the buffer elsewhere without invalidating it") I don't think this follows from the documented contract. select_mapping() requires the exporter to keep the recorded type servable and invalidate before an incompatible move. That obligation still applies if ops->pin() fails. Is retaining the selection after a failed pin intentional? If so, this can be added as a test documenting that alongside the map-failure regression test. Thanks, Karl