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[142.68.128.5]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-45d92e0ed8csm4660151cf.36.2024.10.03.04.16.04 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 03 Oct 2024 04:16:04 -0700 (PDT) Received: from jgg by wakko with local (Exim 4.95) (envelope-from ) id 1swJoR-00AILi-SH; Thu, 03 Oct 2024 08:16:03 -0300 Date: Thu, 3 Oct 2024 08:16:03 -0300 From: Jason Gunthorpe To: Yang Shi Cc: Nicolin Chen , james.morse@arm.com, will@kernel.org, robin.murphy@arm.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [v2 PATCH] iommu/arm-smmu-v3: Fix L1 stream table index calculation for 32-bit sid size Message-ID: <20241003111603.GU1369530@ziepe.ca> References: <20241002175514.1165299-1-yang@os.amperecomputing.com> <1c9767e1-4d05-4650-bc14-65a18fc63cc2@os.amperecomputing.com> <20241002194004.GT1369530@ziepe.ca> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20241003_041607_023368_FEF8A04D X-CRM114-Status: GOOD ( 14.18 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Wed, Oct 02, 2024 at 01:05:08PM -0700, Yang Shi wrote: > > It would make some sense to have something like: > > > > u64 size = arm_smmu_strtab_max_sid() > > > > /* Would require too much memory */ > > if (size > SZ_512M) > > return -EINVAL; > > Why not just check smmu->sid_bits? > > For example, > > if (smmu->sid_bits > 28) >     return -EINVAL; > > The check can happen before the shift. Sure, but IMHO it reads a bit better to check the size computed from the helper MAX_PAGE_ORDER is often 10, so kmalloc will always fail before we reach 28 bits of sid space. Jason