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[82.27.106.168]) by smtp.gmail.com with ESMTPSA id h13-20020a170906590d00b006f39021e683sm1490192ejq.12.2022.04.25.07.27.05 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 25 Apr 2022 07:27:06 -0700 (PDT) Date: Mon, 25 Apr 2022 15:26:40 +0100 From: Jean-Philippe Brucker To: Dave Hansen Cc: "zhangfei.gao@foxmail.com" , Fenghua Yu , Joerg Roedel , Ravi V Shankar , Tony Luck , Ashok Raj , Peter Zijlstra , Dave Hansen , x86 , linux-kernel , iommu , Ingo Molnar , Borislav Petkov , Andy Lutomirski , Josh Poimboeuf , Thomas Gleixner , will@kernel.org, robin.murphy@arm.com, zhangfei.gao@linaro.org Subject: Re: [PATCH v4 05/11] iommu/sva: Assign a PASID to mm on PASID allocation and free it on mm exit Message-ID: References: <76ec6342-0d7c-7c7b-c132-2892e4048fa1@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <76ec6342-0d7c-7c7b-c132-2892e4048fa1@intel.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Apr 25, 2022 at 07:18:36AM -0700, Dave Hansen wrote: > On 4/25/22 06:53, Jean-Philippe Brucker wrote: > > On Sat, Apr 23, 2022 at 07:13:39PM +0800, zhangfei.gao@foxmail.com wrote: > >>>> On 5.17 > >>>> fops_release is called automatically, as well as iommu_sva_unbind_device. > >>>> On 5.18-rc1. > >>>> fops_release is not called, have to manually call close(fd) > >>> Right that's weird > >> Looks it is caused by the fix patch, via mmget, which may add refcount of > >> fd. > > Yes indirectly I think: when the process mmaps the queue, mmap_region() > > takes a reference to the uacce fd. That reference is released either by > > explicit close() or munmap(), or by exit_mmap() (which is triggered by > > mmput()). Since there is an mm->fd dependency, we cannot add a fd->mm > > dependency, so no mmget()/mmput() in bind()/unbind(). > > > > I guess we should go back to refcounted PASIDs instead, to avoid freeing > > them until unbind(). > > Yeah, this is a bit gnarly for -rc4. Let's just make sure there's > nothing else simple we can do. > > How does the IOMMU hardware know that all activity to a given PASID is > finished? That activity should, today, be independent of an mm or a > fd's lifetime. In the case of uacce, it's tied to the fd lifetime: opening an accelerator queue calls iommu_sva_bind_device(), which sets up the PASID context in the IOMMU. Closing the queue calls iommu_sva_unbind_device() which destroys the PASID context (after the device driver stopped all DMA for this PASID). Thanks, Jean