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charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: SA1PR12MB7199.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: 1b779678-3ac4-4dee-d639-08dd7cc3d302 X-MS-Exchange-CrossTenant-originalarrivaltime: 16 Apr 2025 08:51:05.6805 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: z0J7CMfd+RxuedKemwXYUacJsHH+DhA777vgCtT8be9JOGNiuFyWLflkKp2vT20UVH7390UhF6Uaa7hTZNYc5Q== X-MS-Exchange-Transport-CrossTenantHeadersStamped: IA0PR12MB7529 X-Rspam-User: X-Rspamd-Queue-Id: 99089100008 X-Rspamd-Server: rspam04 X-Stat-Signature: t176c9yirpgaehwj7d8izpkdpjidu1k3 X-HE-Tag: 1744793469-357946 X-HE-Meta: U2FsdGVkX19YcX2SudJ/aJWcXrKuJtlf2cTjbud4qKdK+iAvv+bdgZdjqq3kvF4nGrG2DFWn8j2upXMao1Zl2ol2/nQ9fNFwrJHXpqOq55wbJzy9hGC3l85vOQrJnsSEx9J4qZ3nmHUDbNOdzkxhHC1vFfUr3GmWCfftj/m1SNVGeJckUC3a+QVQ5SeWG37gIkP9QKWBFSOsD+iSqYQND9SYrLql/BDJ8lo5tWZFb7nQDXrolravX9YSHtGo1uwhUtzA7cteXsOMlAPtSFl8QaHod1FOdlFCLn2qjPF7DZMlJgi2X4H0PmgJz2zyM+QlyoOX2KtQm9wCSgWZ6pOTTPi6SuOJ9M25oYHKiZZhDjNgeB9WfFLpjCrJtDhdFpGxIIzj5y22Fr4Hu68OTIF4XLKJLE10xevmFUY4ol53M3IxgRhvAM9BTwezNZFfxDO6ZeQ74JpIs6bjrP1R5O6ZR0S7b3cIGbETKz/gtTjDVP2wmPV+TbfnvtKgmmj+fgNGeS0+ZpR+C7a9J/y6iBrjyyGv8GgWEmrp6cv6/LuoNDRPkzPnju48DxtWQ3syDIhF+YbqDimdxsrlPtAeS88MJGzv060f5iCxGM19QWJOzm5AzIhEfAMo8FmWxYKA8ZPQlGBj5YlWVSHNag8z3lJzpV+8HxvhQAH4DW+098Tgen+risKcvTPoGcGu3IkZ4i4ryfICHQ3hSbGGRLLeA4pz0czQb0ironaJd1LBpzSphpt/uFm1d+pfbq1jBvZmnsqjZKQ8UfNVl1iW5Hkaw/yCQdi7FEVUb0x2L7dE4NNLAe2vagquzXr72RWYfKfKb0W9F/xqv25vZr94eUWK9RBr4JHHbG3vR3uLcfIFV9dszPzgcPcxVxN75vLzXwgNBMVkyFWXToXX1VXZrxut025XMmJ3Y90VAeqd1KekrtHLHMe+El7VwmTGqxicdnZgtAtDoDJltMOIsuhQSCVHuaw dDUwTO/j 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi, summarizing the discussion so far and outlining the next steps. The key= points=0A= are as follows:=0A= 1. KVM cap to expose whether the kernel supports mapping cacheable PFNMAP:= =0A= If the host doesn't have FWB, then the capability doesn't exist. Jason, Oli= ver, Caitlin=0A= and Sean points that this may not be required as userspace do not have=0A= much choice anyways. KVM has to follow the PTEs and userspace cannot ask=0A= for something different. However, Marc points that enumerating FWB support= =0A= would allow userspace to discover the support and prevent live-migration=0A= across FWB and non-FWB hosts. Jason suggested that this may still be fine a= s=0A= we have already built in VFIO side protection where a live migration can be= =0A= attempted and then fail because of late-detected HW incompatibilities.=0A= =0A= 2. New memslot flag that VMM passes at memslot registration:=0A= Discussion point that this is not necessary and KVM should just follow the= =0A= VMA pgprot.=0A= =0A= 3. Fallback path handling for PFNMAP when the FWB is not set:=0A= Discussion points that there shouldn't be any fallback path and the memslot= =0A= should just fail. i.e. KVM should not allow degrading cachable to non-cacha= ble=0A= when it can't do flushing. This is to prevent the potential security issue= =0A= pointed by Jason (S1 cacheable, S2 noncacheable).=0A= =0A= =0A= So AIU, the next step is to send out the updated series with the following = patches:=0A= 1. Block cacheable PFN map in memslot creation (kvm_arch_prepare_memory_reg= ion)=0A= and during fault handling (user_mem_abort()).=0A= =0A= 2. Enable support for cacheable PFN maps if S2FWB is enabled by following= =0A= the vma pgprot (this patch).=0A= =0A= 3. Add and expose the new KVM cap to expose cacheable PFNMAP (set to false= =0A= for !FWB), pending maintainers' feedback on the necessity of this capabilit= y.=0A= =0A= Please let me know if there are any inaccuracies.=0A= =0A= Thanks=0A= Ankit Agrawal=0A= =0A=