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Fri, 07 Aug 2026 11:20:18 -0700 (PDT) Received: from jgg by wakko with local (Exim 4.97) (envelope-from ) id 1wsPB3-00000001Bmx-1xNi; Fri, 07 Aug 2026 15:20:17 -0300 Date: Fri, 7 Aug 2026 15:20:17 -0300 From: Jason Gunthorpe To: Mostafa Saleh Cc: Will Deacon , "Aneesh Kumar K.V" , iommu@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-coco@lists.linux.dev, Robin Murphy , Marek Szyprowski , Marc Zyngier , Steven Price , Suzuki K Poulose , Catalin Marinas , Jiri Pirko , Petr Tesarik , Alexey Kardashevskiy , Dan Williams , Xu Yilun , linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, Madhavan Srinivasan , Michael Ellerman , Nicholas Piggin , Christophe Leroy , Alexander Gordeev , Gerald Schaefer , Heiko Carstens , Vasily Gorbik , Christian Borntraeger , Sven Schnelle , x86@kernel.org Subject: Re: [PATCH] arm64: swiotlb: Keep the default size for protected guests Message-ID: <20260807182017.GH200537@ziepe.ca> References: <20260717180442.110954-18-aneesh.kumar@kernel.org> <20260807092612.2202005-1-aneesh.kumar@kernel.org> <20260807135810.GA200537@ziepe.ca> <20260807164734.GE200537@ziepe.ca> Precedence: bulk X-Mailing-List: linux-coco@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, Aug 07, 2026 at 06:13:49PM +0000, Mostafa Saleh wrote: > But the whole thing is best effort anyway, the kernel picks > IO_TLB_DEFAULT_SIZE which does not depend on the system topology or > how many devices or how much DMA they do. > SWIOTLB memory is wasted if unused so we should be careful around > that as it would be the other way around and users would have to > decrease it manually. Yeah, it is why the arch code shouldn't really be sizing it directly, it should be done in common code and, yes, we are probably going to have to do something alot smarter to have the common code better auto-tune this for the CC case.. Jason