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Tue, 1 Jul 2025 06:05:43 +0000 Date: Tue, 1 Jul 2025 14:03:04 +0800 From: Yan Zhao To: Vishal Annapurve CC: "Edgecombe, Rick P" , "ackerleytng@google.com" , "quic_eberman@quicinc.com" , "Li, Xiaoyao" , "Shutemov, Kirill" , "Hansen, Dave" , "david@redhat.com" , "thomas.lendacky@amd.com" , "vbabka@suse.cz" , "tabba@google.com" , "Du, Fan" , "michael.roth@amd.com" , "seanjc@google.com" , "binbin.wu@linux.intel.com" , "Peng, Chao P" , "kvm@vger.kernel.org" , "Yamahata, Isaku" , "linux-kernel@vger.kernel.org" , "Weiny, Ira" , "pbonzini@redhat.com" , "Li, Zhiquan1" , "jroedel@suse.de" , "Miao, Jun" , "pgonda@google.com" , "x86@kernel.org" Subject: Re: [RFC PATCH 08/21] KVM: TDX: Increase/decrease folio ref for huge pages Message-ID: Reply-To: Yan Zhao References: <447bae3b7f5f2439b0cb4eb77976d9be843f689b.camel@intel.com> <4cbdfd3128a6dcc67df41b47336a4479a07bf1bd.camel@intel.com> Content-Type: text/plain; charset="utf-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-ClientProxiedBy: SG2P153CA0031.APCP153.PROD.OUTLOOK.COM (2603:1096:4:c7::18) To DS7PR11MB5966.namprd11.prod.outlook.com (2603:10b6:8:71::6) Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DS7PR11MB5966:EE_|DS4PPF7CCC4B437:EE_ X-MS-Office365-Filtering-Correlation-Id: 854a32b7-0f44-4260-31f6-08ddb865501a X-LD-Processed: 46c98d88-e344-4ed4-8496-4ed7712e255d,ExtAddr X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|366016|7416014|376014; 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Have the arch/x86 side of TDX grow > > > > > a > > > > > new tdx_buggy_shutdown(). Have it do an all-cpu IPI to kick CPUs out of > > > > > SEAMMODE, wbivnd, and set a "no more seamcalls" bool. Then any SEAMCALLs > > > > > after > > > > > that will return a TDX_BUGGY_SHUTDOWN error, or similar. All TDs in the > > > > > system > > > > > die. Zap/cleanup paths return success in the buggy shutdown case. > > > > > > > > > > > > > Do you mean that on unmap/split failure: > > > > > > Maybe Yan can clarify here. I thought the HWpoison scenario was about TDX module > > My thinking is to set HWPoison to private pages whenever KVM_BUG_ON() was hit in > > TDX. i.e., when the page is still mapped in S-EPT but the TD is bugged on and > > about to tear down. > > > > So, it could be due to KVM or TDX module bugs, which retries can't help. > > > > > bugs. Not TDX busy errors, demote failures, etc. If there are "normal" failures, > > > like the ones that can be fixed with retries, then I think HWPoison is not a > > > good option though. > > > > > > > there is a way to make 100% > > > > sure all memory becomes re-usable by the rest of the host, using > > > > tdx_buggy_shutdown(), wbinvd, etc? > > > > Not sure about this approach. When TDX module is buggy and the page is still > > accessible to guest as private pages, even with no-more SEAMCALLs flag, is it > > safe enough for guest_memfd/hugetlb to re-assign the page to allow simultaneous > > access in shared memory with potential private access from TD or TDX module? > > If no more seamcalls are allowed and all cpus are made to exit SEAM > mode then how can there be potential private access from TD or TDX > module? Not sure. As Kirill said "TDX module has creative ways to corrupt it" https://lore.kernel.org/all/zlxgzuoqwrbuf54wfqycnuxzxz2yduqtsjinr5uq4ss7iuk2rt@qaaolzwsy6ki/. Or, could TDX just set a page flag, like what for XEN /* XEN */ /* Pinned in Xen as a read-only pagetable page. */ PG_pinned = PG_owner_priv_1, e.g. PG_tdx_firmware_access = PG_owner_priv_1, Then, guest_memfd checks this flag on every zap and replace it with PG_hwpoison on behalf of TDX?