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[142.162.112.119]) by smtp.gmail.com with ESMTPSA id af79cd13be357-8caf7aeed7dsm163905385a.18.2026.02.06.07.07.08 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 06 Feb 2026 07:07:08 -0800 (PST) Received: from jgg by wakko with local (Exim 4.97) (envelope-from ) id 1voNQJ-00000008ZWC-2gJs; Fri, 06 Feb 2026 11:07:07 -0400 Date: Fri, 6 Feb 2026 11:07:07 -0400 From: Jason Gunthorpe To: Bjorn Helgaas Cc: Manivannan Sadhasivam , Manivannan Sadhasivam , Bjorn Helgaas , linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org, iommu@lists.linux.dev, Naresh Kamboju , Pavankumar Kondeti , Xingang Wang , Marek Szyprowski , Robin Murphy , Alex Williamson , James Puthukattukaran Subject: Re: [PATCH v3 3/4] PCI: Disable ACS SV capability for the broken IDT switches Message-ID: <20260206150707.GM943673@ziepe.ca> References: <20260206145254.GK943673@ziepe.ca> <20260206150505.GA58808@bhelgaas> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260206150505.GA58808@bhelgaas> On Fri, Feb 06, 2026 at 09:05:05AM -0600, Bjorn Helgaas wrote: > On Fri, Feb 06, 2026 at 10:52:54AM -0400, Jason Gunthorpe wrote: > > On Fri, Feb 06, 2026 at 08:46:51AM -0600, Bjorn Helgaas wrote: > > > > > IIUC the current situation is that for these IDT switches, ACS SV is > > > enabled when downstream devices are passed through to guests, but > > > after these patches, it will no longer be enabled. > > > > ACS SV is enabled at boot time if an IOMMU driver is present > > regardless if guests or virtualization is in use. > > > > Linux doesn't change ACS flags dynamically. > > Right, it's just that this series effectively un-advertises ACS SV for > the IDE switches so it will never be enabled for them Yes > > iommu_groups will correctly describe the system limitations with the > > ACS quirk path and so all of the above concerns are taken care > > of. Robin is saying the Juno SMMU forces a large iommu_group covering > > the switch anyhow today, so at least that platform is not affected. > > I guess REQ_ACS_FLAGS is what iommu_groups looks for? I looked for > such a thing earlier but must have missed it. Thanks! Yes Jason