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Thu, 22 Oct 2026 08:47:27 +0000 Date: Thu, 22 Oct 2026 16:46:29 +0800 From: Yan Zhao To: "Edgecombe, Rick P" CC: "Du, Fan" , "kvm@vger.kernel.org" , "kai.huang@intel.com" , "Li, Xiaoyao" , "Hansen, Dave" , "thomas.lendacky@amd.com" , "tabba@google.com" , "vbabka@suse.cz" , "david@kernel.org" , "michael.roth@amd.com" , "binbin.wu@linux.intel.com" , "seanjc@google.com" , "kas@kernel.org" , "pbonzini@redhat.com" , "ackerleytng@google.com" , "Peng, Chao P" , "nik.borisov@suse.com" , "linux-kernel@vger.kernel.org" , "sagis@google.com" , "Annapurve, Vishal" , "Chen, Farrah" , "Gao, Chao" , "francescolavra.fl@gmail.com" , "Miao, Jun" , "jgross@suse.com" , "pgonda@google.com" , "x86@kernel.org" Subject: Re: [PATCH v4 02/17] x86/virt/tdx: Add a SEAMCALL wrapper to demote a 2MB huge page Message-ID: Reply-To: Yan Zhao References: <94e930e88046fca1f53d2234d581aae593367d95.camel@intel.com> <19661a3ed2089304fd69ab4ca117eca7ceba425c.camel@intel.com> Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <19661a3ed2089304fd69ab4ca117eca7ceba425c.camel@intel.com> X-ClientProxiedBy: SI1PR02CA0037.apcprd02.prod.outlook.com (2603:1096:4:1f6::13) To BL0PR11MB3236.namprd11.prod.outlook.com (2603:10b6:208:60::18) 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 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: BL0PR11MB3236:EE_|DS0PR11MB7458:EE_ X-MS-Office365-Filtering-Correlation-Id: a12ae930-8b35-4de7-b58f-08df301919b6 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|23010399003|366016|376014|7416014|6133799003|261021121427099003|22082099003|18002099003|10067099003|4143699003|11063799006|261009223027099003|56012099006; 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Any new functions or extra code will get scrutiny. > > I agree! > > (my only concern is the risk of NULL pointer dereference). > > As above, let's just match the existing code. Otherwise I think its just going > to get questions and not merged. We want this to have as little to talk about as > possible. If we want to change the defensive level (I don't), it is going to > need a bunch of prep patches instead of just embarking on a new paradigm for > additional huge page functions. I don't see a need to do that, and for the sake > of getting basic huge page support, I think that is a good thing. Right? Thanks, I'll follow your suggestion. Does the following code look good to you? u64 tdh_mem_page_demote_2mb(struct tdx_td *td, u64 gpa, kvm_pfn_t pfn, struct page *new_sept_pt, struct tdx_pamt_cache *pamt_cache, u64 *ext_err1, u64 *ext_err2) { struct tdx_module_args args = { .rcx = gpa | pg_level_to_tdx_sept_level(PG_LEVEL_2M), .rdx = tdx_tdr_pa(td), .r8 = page_to_phys(new_sept_pt), }; struct page *dpamt_pages[TDX_DPAMT_ENTRY_PAGE_CNT]; atomic_t *dpamt_refcount; u64 ret; /* * For implementation simplicity, only support demotion when * DPAMT is enabled. */ WARN_ON_ONCE(!tdx_supports_dynamic_pamt(&tdx_sysinfo)); /* A NULL pamt_cache is unexpected, so failure indicates a software error */ ret = alloc_pamt_array(dpamt_pages, pamt_cache); if (ret) { *ext_err1 = 0; *ext_err2 = 0; return TDX_SW_ERROR; } dpamt_refcount = tdx_find_dpamt_refcount(pfn); args.r12 = page_to_phys(dpamt_pages[0]); args.r13 = page_to_phys(dpamt_pages[1]); /* * The dpamt_lock is used to avoid contention between the * TDH_MEM_PAGE_DEMOTE and TDH_PHYMEM_PAMT_{ADD/REMOVE} SEAMCALLs. */ spin_lock(&dpamt_lock); ret = seamcall_saved_ret(TDH_MEM_PAGE_DEMOTE, &args); *ext_err1 = args.rcx; *ext_err2 = args.rdx; if (WARN_ON_ONCE(ret != TDX_SUCCESS)) goto out_free; atomic_set(dpamt_refcount, PTRS_PER_PMD); spin_unlock(&dpamt_lock); return TDX_SUCCESS; out_free: spin_unlock(&dpamt_lock); free_pamt_array(pamt_cache, dpamt_pages); return ret; } EXPORT_SYMBOL_FOR_KVM(tdh_mem_page_demote_2mb);