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[35.189.192.250]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-c4d0e41d670sm54601366b.23.2026.11.04.02.27.50 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 04 Nov 2026 02:27:50 -0800 (PST) Date: Wed, 4 Nov 2026 10:27:43 +0000 From: Mostafa Saleh To: Jacob Pan Cc: iommu@lists.linux.dev, Jason Gunthorpe , 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: [PATCH RFC 1/9] iommu: Introduce external attach domain type Message-ID: References: <20260925190742.1575380-1-jacob.pan@linux.microsoft.com> <20260925190742.1575380-2-jacob.pan@linux.microsoft.com> <20261026161003.00003b71@linux.microsoft.com> X-Mailing-List: linux-kernel@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: <20261026161003.00003b71@linux.microsoft.com> On Mon, Oct 26, 2026 at 04:10:03PM -0700, Jacob Pan wrote: > Hi Mostafa, > > On Wed, 21 Oct 2026 10:57:20 +0000 > Mostafa Saleh wrote: > > > On Fri, Sep 25, 2026 at 12:07:34PM -0700, Jacob Pan wrote: > > > Add IOMMU_DOMAIN_EXTERNAL for externally managed domains that move > > > or attach devices to another VM address space provisioned by an > > > external owner, such as a type 1 hypervisor. > > > > > > This is not a paging domain and is not sysfs-selectable as a default > > > domain type. It requires external owner context, such as a vIOMMU. > > > > > > > Can't we use a IOMMU_DOMAIN_BLOCKED domain for that, AFAIU, the host > > never inserts any mapping? > Right, the host does not own or install any mappings. > > The external domain type is nevertheless useful for two reasons: > > 1. It allows the pvIOMMU driver's domain ops to do the MSHV & Xen attach > and detach hypercalls > 2. It allows an externally managed device to leverage the normal IOMMUFD > device-to-HWPT attachment interface: VFIO_DEVICE_ATTACH_IOMMUFD_PT > No new ioctls. > > It also makes the lifetime and ownership clear for IOMMUFD and > hypervisor, the device can be returned back to host iommufd owned > domains once detached. > > In pKVM case, my understanding is that you have a emulated root SMMU > which does not do hypercalls obviously. Then the external attach > is done via an "out of tree uAPI through KVM/VFIO bridge IOCTLs that > proxies those hypercalls." > > Therefore, if we were to park the device in blocking domain while doing > external attach (as you suggested), this requires a new PV only uAPI > that must support pkvm, MSHV, and Xen. So it does not fit in the flow > supported by PV IOMMU root driver. I am not sure I understand this, how can the domain type change the uAPI? can you please point to what breaks in the code if a blocking domain was used? Thanks, Mostafa > > I don't have a better solution for both pv and emulated root IOMMU > drivers. Perhaps others do? >