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X-CSE-ConnectionGUID: FxbJfzuQQxOcLqTBGrjqlQ== X-CSE-MsgGUID: T/FQdD7SQnyXm4mQYF1csw== X-IronPort-AV: E=McAfee;i="6800,10657,11476"; a="52519542" X-IronPort-AV: E=Sophos;i="6.16,268,1744095600"; d="scan'208";a="52519542" Received: from orviesa004.jf.intel.com ([10.64.159.144]) by fmvoesa112.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 26 Jun 2025 15:33:12 -0700 X-CSE-ConnectionGUID: 2YrduJMoTOm3og1aSVyK4A== X-CSE-MsgGUID: PKzka5DvQv2VTCcjFUDAEA== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.16,268,1744095600"; d="scan'208";a="157202618" Received: from aschofie-mobl2.amr.corp.intel.com (HELO [10.125.109.42]) ([10.125.109.42]) by orviesa004-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 26 Jun 2025 15:33:12 -0700 Message-ID: Date: Thu, 26 Jun 2025 15:33:11 -0700 Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 2/2] KVM: TDX: Do not clear poisoned pages To: "Huang, Kai" , "Luck, Tony" , "Hunter, Adrian" , "Annapurve, Vishal" Cc: "kvm@vger.kernel.org" , "Li, Xiaoyao" , "Zhao, Yan Y" , "dave.hansen@linux.intel.com" , "kirill.shutemov@linux.intel.com" , "mingo@redhat.com" , "seanjc@google.com" , "linux-kernel@vger.kernel.org" , "tglx@linutronix.de" , "Yamahata, Isaku" , "tony.lindgren@linux.intel.com" , "binbin.wu@linux.intel.com" , "linux-edac@vger.kernel.org" , "hpa@zytor.com" , "Chatre, Reinette" , "pbonzini@redhat.com" , "Edgecombe, Rick P" , "bp@alien8.de" , "Gao, Chao" , "x86@kernel.org" References: <20250618120806.113884-1-adrian.hunter@intel.com> <20250618120806.113884-3-adrian.hunter@intel.com> <68938275-3f6a-46fc-9b38-2c916fdec3d6@intel.com> <91df7051-2405-4609-9e86-2bbc02829644@intel.com> <8c24d9b9c888eed972e8ee75fa9d31cc7fd72a73.camel@intel.com> From: Dave Hansen Content-Language: en-US Autocrypt: addr=dave.hansen@intel.com; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 6/26/25 15:20, Huang, Kai wrote: > But IMHO we may should just have a simple policy that when a page is marked > as poisoned, it should never be touched again. It's only one page anyway > (for one TD) so losing that doesn't seem bad to me. If we want to clear the > poisoned page, then perhaps we should mark that page to be not-poisoned > again. The simplest policy is to do nothing. The kernel only has 29 places that check PageHWPoison(). I'd guess that roughly half of those are the memory-failure.c infrastructure and bare-minimum code to handle poison, like not allowing pages to go back into the allocator. There are something like 5,000 lines of code in the kernel that deal with a literal 'struct page'. 29 checks for ~5,000 sites is pretty minuscule. We obviously don't have a policy that every place that uses 'struct page' needs to check for poison. We also don't even have a policy where writes to or reads from a page check for poison. Why is this TDX code so special that PageHWPoison() needs to be checked. For instance: $ grep -r PageHWPoison arch/x86/ arch/x86/kernel/cpu/mce/core.c: SetPageHWPoison(p); arch/x86/kernel/cpu/mce/core.c: SetPageHWPoison(p); In other words, this would be the *ONLY* arch/x86 site. Why?