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Tue, 5 Aug 2025 19:06:13 +0000 From: Date: Tue, 5 Aug 2025 12:06:11 -0700 To: Jason Gunthorpe , CC: Aneesh Kumar K.V , , , , , , , "Samuel Ortiz" , Xu Yilun , "Suzuki K Poulose" , Steven Price , Catalin Marinas , Marc Zyngier , Will Deacon , Oliver Upton Message-ID: <6892562356e53_55f0910010@dwillia2-xfh.jf.intel.com.notmuch> In-Reply-To: <20250805184219.GZ26511@ziepe.ca> References: <20250728135216.48084-1-aneesh.kumar@kernel.org> <688c2155849a2_cff99100dd@dwillia2-xfh.jf.intel.com.notmuch> <20250801155104.GC26511@ziepe.ca> <688d2f7ac39ce_cff9910024@dwillia2-xfh.jf.intel.com.notmuch> <20250805172741.GX26511@ziepe.ca> <68924d18a68d4_55f091004d@dwillia2-xfh.jf.intel.com.notmuch> <20250805184219.GZ26511@ziepe.ca> Subject: Re: [RFC PATCH v1 00/38] ARM CCA Device Assignment support Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable X-ClientProxiedBy: BYAPR03CA0010.namprd03.prod.outlook.com (2603:10b6:a02:a8::23) To PH8PR11MB8107.namprd11.prod.outlook.com (2603:10b6:510:256::6) Precedence: bulk X-Mailing-List: linux-pci@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: PH8PR11MB8107:EE_|PH0PR11MB4824:EE_ X-MS-Office365-Filtering-Correlation-Id: 0d14c44d-daf5-4677-8130-08ddd453256d X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|366016|376014|7416014; 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So ok not to not NOP in this specific path, > > right? >=20 > What I said in my other mail was the the T=3D1 state should have nothing > to do with driver binding. Guest driver unbind, agree. > So unbinding vfio should leave the device in the RUN state just fine. Perhaps my vfio inexperience is showing, but at the point where the VMM is unbinding vfio it is committed to destroying the guest's assigned device context, no? So should that not be the point where continuing to maintain the RUN state ends? > > > With the ideal version being the TSM and VMM would be able to block > > > the iommu as a functional stand in for BME. > >=20 > > The TSM block for BME is the LOCKED or ERROR state. That would be in > > conflict with the proposal that the device stays in the RUN state on > > guest driver unbind. >=20 > This is a different thing. Leaving RUN says the OS (especially > userspace) does not trust the device. >=20 > Disabling DMA, on explict trusted request from the cVM, is entirely > fine to do inside the T=3D1 state. PCI made it so the only way to do > this is with the IOMMU, oh well, so be it. >=20 > > I feel like either the device stays in RUN state and BME leaks, or the > > device is returned to LOCKED on driver unbind.=20 >=20 > Stay in RUN is my vote. I can't really defend the other choice from a > linux driver model perspective. >=20 > > Otherwise a functional stand-in for BME that also keeps the device > > in RUN state feels like a TSM feature request for a "RUN but > > BLOCKED" state. >=20 > Yes, and probably not necessary, more of a defence against bugs in > depth kind of request. For Linux we would like it if the device can be > in RUN and have DMA blocked off during all times when no driver is > attached. Ok, defense in depth, but in the meantime rely on unbound driver =3D=3D DMA unmapped and device should be quiescent. Combine that with the fact that userspace PCI drivers should be disabled in cVMs should mean that guest can expect that an unbound TDI in the RUN state will remain quiet.=