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[142.68.80.239]) by smtp.gmail.com with ESMTPSA id u10-20020a0cdd0a000000b0069b60baec46sm4402412qvk.146.2024.04.22.12.31.00 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 22 Apr 2024 12:31:00 -0700 (PDT) Received: from jgg by wakko with local (Exim 4.95) (envelope-from ) id 1ryzNT-0015IM-Mf; Mon, 22 Apr 2024 16:30:59 -0300 Date: Mon, 22 Apr 2024 16:30:59 -0300 From: Jason Gunthorpe To: Baolu Lu Cc: Tomasz Jeznach , Joerg Roedel , Will Deacon , Robin Murphy , Paul Walmsley , Palmer Dabbelt , Albert Ou , Anup Patel , Sunil V L , Nick Kossifidis , Sebastien Boeuf , Rob Herring , Krzysztof Kozlowski , Conor Dooley , devicetree@vger.kernel.org, iommu@lists.linux.dev, linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, linux@rivosinc.com Subject: Re: [PATCH v2 7/7] iommu/riscv: Paging domain support Message-ID: <20240422193059.GC231144@ziepe.ca> References: <301244bc3ff5da484b46d3fecc931cdad7d2806f.1713456598.git.tjeznach@rivosinc.com> <2f2750cd-a5bf-4486-8f50-c93d246f8b0c@linux.intel.com> Precedence: bulk X-Mailing-List: iommu@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2f2750cd-a5bf-4486-8f50-c93d246f8b0c@linux.intel.com> On Mon, Apr 22, 2024 at 01:21:05PM +0800, Baolu Lu wrote: > > + /* Track domain to devices mapping. */ > > + if (bond) > > + list_add_rcu(&bond->list, &domain->bonds); > > + > > + /* Remove tracking from previous domain, if needed. */ > > + iommu_domain = iommu_get_domain_for_dev(dev); > > Calling iommu_get_domain_for_dev() in the domain attaching path is very > fragile because it heavily depends on the order of calling the attach > callback and setting the domain pointer in the core. We have a couple places doing this already, the core code accomodates it well enough for deleting from a list.. So I think it is OK to keep doing. > Perhaps the driver can use dev_iommu_priv_set/get() to keep the active > domain in the per-device private data? > > > + if (iommu_domain && !!(iommu_domain->type & __IOMMU_DOMAIN_PAGING)) { > > + domain = iommu_domain_to_riscv(iommu_domain); > > + bond = NULL; > > + rcu_read_lock(); > > + list_for_each_entry_rcu(b, &domain->bonds, list) { > > + if (b->dev == dev) { > > + bond = b; > > + break; > > + } > > + } > > + rcu_read_unlock(); But now that I look again, this is not safe, you have to hold some kind of per-domain lock to mutate the list. rcu_*read*_lock() cannot be used for write. Jason