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Mon, 20 Apr 2020 11:45:03 +0000 Subject: Re: [PATCH v5 02/25] iommu/sva: Manage process address spaces To: Christoph Hellwig , Jean-Philippe Brucker Cc: iommu@lists.linux-foundation.org, devicetree@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-pci@vger.kernel.org, linux-mm@kvack.org, joro@8bytes.org, catalin.marinas@arm.com, will@kernel.org, robin.murphy@arm.com, kevin.tian@intel.com, baolu.lu@linux.intel.com, Jonathan.Cameron@huawei.com, jacob.jun.pan@linux.intel.com, zhangfei.gao@linaro.org, jgg@ziepe.ca, xuzaibo@huawei.com References: <20200414170252.714402-1-jean-philippe@linaro.org> <20200414170252.714402-3-jean-philippe@linaro.org> <20200416072852.GA32000@infradead.org> <20200416085402.GB1286150@myrica> <20200416121331.GA18661@infradead.org> <20200420074213.GA3180232@myrica> <20200420081034.GA17305@infradead.org> From: =?UTF-8?Q?Christian_K=c3=b6nig?= Message-ID: <6b195512-fa73-9a49-03d8-1ed92e86f607@amd.com> Date: Mon, 20 Apr 2020 13:44:56 +0200 User-Agent: Mozilla/5.0 (X11; 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I still like having a single mmu notifier 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->pasid, >> 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. Regards, Christian.