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See http://www.infradead.org/rpr.html Cc: Jean-Philippe Brucker , kevin.tian@intel.com, devicetree@vger.kernel.org, jgg@ziepe.ca, linux-pci@vger.kernel.org, robin.murphy@arm.com, linux-mm@kvack.org, iommu@lists.linux-foundation.org, catalin.marinas@arm.com, zhangfei.gao@linaro.org, will@kernel.org, linux-arm-kernel@lists.infradead.org X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" On Mon, Apr 20, 2020 at 01:44:56PM +0200, Christian K=F6nig wrote: > Am 20.04.20 um 10:10 schrieb Christoph Hellwig: > > On Mon, Apr 20, 2020 at 09:42:13AM +0200, Jean-Philippe Brucker wrote: > > > Right, I can see the appeal. I still like having a single mmu notifie= r per > > > mm because it ensures we allocate a single PASID per mm (as required = by > > > x86). I suppose one alternative is to maintain a hashtable of mm->pas= id, > > > to avoid iterating over all bonds during allocation. > > Given that the PASID is a pretty generic and important concept can > > we just add it directly to the mm_struct and allocate it lazily once > > we first need it? > = > Well the problem is that the PASID might as well be device specific. E.g. > some devices use 16bit PASIDs, some 15bit, some other only 12bit. > = > So what could (at least in theory) happen is that you need to allocate > different PASIDs for the same process because different devices need one. This directly contradicts the statement from Jean-Philippe above that x86 requires a single PASID per mm_struct. If we may need different PASIDs for different devices and can actually support this just allocating one per [device, mm_struct] would make most sense of me, as it doesn't couple otherwise disjoint state. _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu