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[159.2.239.150]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-54b10c49ab3sm28279301cf.19.2026.11.04.09.04.23 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 04 Nov 2026 09:04:23 -0800 (PST) Received: from jgg by wakko with local (Exim 4.97) (envelope-from ) id 1xOePP-0000000Gg2b-0y2m; Wed, 04 Nov 2026 13:04:23 -0400 Date: Wed, 4 Nov 2026 13:04:23 -0400 From: Jason Gunthorpe To: Mostafa Saleh Cc: Jacob Pan , iommu@lists.linux.dev, Nicolin Chen , Kevin Tian , Will Deacon , Robin Murphy , Wei Liu , "K . Y . Srinivasan" , Haiyang Zhang , Dexuan Cui , Long Li , linux-hyperv@vger.kernel.org, Joerg Roedel , Suravee Suthikulpanit , Vasant Hegde , Arnd Bergmann , linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, "Aneesh Kumar K . V" , Mukesh Rathor , John Starks , Souradeep Chakrabarti , Yu Zhang , Easwar Hariharan , Alex Williamson Subject: Re: [RFC PATCH 0/9] iommu/iommufd: Add hypervisor external attach Message-ID: <20261104170423.GR3889730@ziepe.ca> References: <20260925190742.1575380-1-jacob.pan@linux.microsoft.com> <20261026114917.00005a22@linux.microsoft.com> X-Mailing-List: linux-arch@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Wed, Nov 04, 2026 at 10:23:22AM +0000, Mostafa Saleh wrote: > > IMHO, I don't see any change needed for the host-side attach between hw > > nested and collapsed single stage, if guest and host attach are > > split. I think it is up to pKVM or MSHV to handle guest virtual iommu > > mapping for both cases. > > Although the hypervisor (pKVM, MSHV) is managing the guest IOMMU in that > case, I believe the host should be able to decide the guest virtual > toplology, as that will impact the firmware tables populated from the > host for example, as in the nested case the guest will see an > architectural SMMUv3 while in the collapsed case it will see a simple > HVC based IOMMU. Yes, this is how RMM/etc are working in CC land. Untrusted hypervisor defines the vPCI topology, trusted hypervisor implements it as instructed. Jason