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Tue, 14 Jul 2026 09:57:54 -0400 (EDT) Date: Tue, 14 Jul 2026 07:57:53 -0600 From: Alex Williamson To: fengchengwen Cc: , , , , , , , , , , alex@shazbot.org Subject: Re: [PATCH v19 12/18] vfio/pci: Add dmabuf TPH metadata storage and fd query helper Message-ID: <20260714075753.20052573@shazbot.org> In-Reply-To: <0768658f-de72-4ddb-a44b-e91a7e294b20@huawei.com> References: <20260702124224.57168-1-fengchengwen@huawei.com> <20260702124224.57168-13-fengchengwen@huawei.com> <20260708173117.3e399c4b@shazbot.org> <20260709125012.21784d0a@shazbot.org> <0768658f-de72-4ddb-a44b-e91a7e294b20@huawei.com> X-Mailer: Claws Mail 4.4.0 (GTK 3.24.52; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: linux-pci@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Tue, 14 Jul 2026 18:46:51 +0800 fengchengwen wrote: > On 7/10/2026 2:50 AM, Alex Williamson wrote: > > > > Additionally, dma_buf_get_pci_tph() defines that the provided values > > are only valid until invalidate_mappings, but this series has no > > plumbing to honor that requirement. > > > > This needs significant work if we need to track the lifecycle of every > > dmabuf related TPH value. Thanks, > > Is it possible to use this as a risk warning? After all, even if the > invalid mapping is performed, the ST only causes performance loss to > the system, and there will be no function problems. Seems like the sort of thing that should have been resolved BEFORE sending out v20. By the same argument, maybe it's sufficient to zero invalidated STs automatically, but we can only do that for IV mode in-kernel and rely on userspace to perform the same for DS mode, but regardless, no mechanism is proposed to perform such invalidation. IMO, this brings into question the supportability of STs provided through dmabufs. It would seem vfio-pci needs to become an importer of the dmabuf, rather than simply scraping TPH data from it, but maybe it can only be supported in IV mode. We don't have a means to represent that. Alex