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[142.68.128.5]) by smtp.gmail.com with ESMTPSA id af79cd13be357-7c36fef4638sm256646585a.25.2025.02.28.06.53.26 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 28 Feb 2025 06:53:27 -0800 (PST) Received: from jgg by wakko with local (Exim 4.97) (envelope-from ) id 1to1jx-00000000Rdk-40J0; Fri, 28 Feb 2025 10:53:25 -0400 Date: Fri, 28 Feb 2025 10:53:25 -0400 From: Jason Gunthorpe To: "Tian, Kevin" Cc: Baolu Lu , Vasant Hegde , Robin Murphy , "Liu, Yi L" , "iommu@lists.linux.dev" , "joro@8bytes.org" , "will@kernel.org" , "suravee.suthikulpanit@amd.com" Subject: Re: [PATCH] iommu/amd: Add Secure ATS support Message-ID: <20250228145325.GK5011@ziepe.ca> References: <20250225105829.52223-1-vasant.hegde@amd.com> <20250225145518.GJ545008@ziepe.ca> <26fa08c1-4a3c-44a6-aba6-a35a0f308bc8@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: On Fri, Feb 28, 2025 at 06:15:32AM +0000, Tian, Kevin wrote: > scenarios. Probably good for prototype development but no > real value given it loses all perf benefit from ATS or even worse > perf compared to no ats due to double walking. ARM's docs noted they expect about the same IO performance between #3 and #4 methods. Both are walking tables to validate the TA. The main value of ATS here is not for performance but it supports a non-present result. So I thik given the choice we should prefer #3 over #4. You must switch to #4 for CXL/etc/etc. Jason