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[142.167.56.70]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-6fb35c84148sm50822446d6.109.2025.06.16.06.20.32 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 16 Jun 2025 06:20:32 -0700 (PDT) Received: from jgg by wakko with local (Exim 4.97) (envelope-from ) id 1uR9lH-00000005gVt-3sIA; Mon, 16 Jun 2025 10:20:31 -0300 Date: Mon, 16 Jun 2025 10:20:31 -0300 From: Jason Gunthorpe To: Demi Marie Obenour Subject: Re: Virtio-IOMMU interrupt remapping design Message-ID: <20250616132031.GB1354058@ziepe.ca> References: <> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Message-ID-Hash: 42JMT7GHMSPMIGJSMNGFKTS5S7EDLJGY X-Message-ID-Hash: 42JMT7GHMSPMIGJSMNGFKTS5S7EDLJGY X-MailFrom: jgg@ziepe.ca X-Mailman-Rule-Misses: dmarc-mitigation; no-senders; approved; emergency; loop; banned-address; member-moderation; header-match-devel.spectrum-os.org-0; header-match-devel.spectrum-os.org-1; header-match-devel.spectrum-os.org-2; header-match-devel.spectrum-os.org-3; header-match-devel.spectrum-os.org-4; nonmember-moderation; administrivia; implicit-dest; max-recipients; max-size; news-moderation; no-subject; digests; suspicious-header CC: "Michael S. Tsirkin" , Jason Wang , Xuan Zhuo , Eugenio =?utf-8?B?UMOpcmV6?= , "Rafael J. Wysocki" , Len Brown , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , Joerg Roedel , Will Deacon , Robin Murphy , Alyssa Ross , virtualization@lists.linux.dev, linux-kernel@vger.kernel.org, linux-acpi@vger.kernel.org, iommu@lists.linux.dev, x86@kernel.org, Spectrum OS Development X-Mailman-Version: 3.3.9 Precedence: list List-Id: Patches and low-level development discussion Archived-At: List-Archive: List-Help: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: On Sun, Jun 15, 2025 at 02:47:15PM -0400, Demi Marie Obenour wrote: > Is a paravirtualized IOMMU with interrupt remapping something that makes > sense? IMHO linking interrupt remapping to the iommu is a poor design, interrupt routing belongs in the irq subsystem, not in the iommu. The fact AMD and Intel both coupled their interrupt routing to their iommu hardware is just a weird design decision. ARM didn't do this, for instance. So I would not try to do this at all, you should have a para-virtualized IRQ interface, not an extension to virtio-iommu adding interrupt handling. :\ AFAIK hyperv shows how to build something like this. Jason