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X-CSE-ConnectionGUID: 6ubiOSmXTiCLzl2JIN97pQ== X-CSE-MsgGUID: PfuPcXl1Qrijucho6n8tKA== X-IronPort-AV: E=McAfee;i="6800,10657,11486"; a="57847716" X-IronPort-AV: E=Sophos;i="6.16,293,1744095600"; d="scan'208";a="57847716" Received: from orviesa007.jf.intel.com ([10.64.159.147]) by orvoesa106.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 06 Jul 2025 21:21:17 -0700 X-CSE-ConnectionGUID: L7NH3yrqQ9C7wxVZCoa6Ug== X-CSE-MsgGUID: uVNuWhqHRm2sNC23TsjmZw== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.16,293,1744095600"; d="scan'208";a="155234252" Received: from spandruv-mobl4.amr.corp.intel.com (HELO [10.125.110.88]) ([10.125.110.88]) by orviesa007-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 06 Jul 2025 21:21:17 -0700 Message-ID: Date: Sun, 6 Jul 2025 21:23:05 -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 V2 2/2] x86/tdx: Skip clearing reclaimed pages unless X86_BUG_TDX_PW_MCE is present To: Chao Gao , Adrian Hunter Cc: Dave Hansen , pbonzini@redhat.com, seanjc@google.com, vannapurve@google.com, Tony Luck , Borislav Petkov , Thomas Gleixner , Ingo Molnar , x86@kernel.org, H Peter Anvin , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, rick.p.edgecombe@intel.com, kirill.shutemov@linux.intel.com, kai.huang@intel.com, reinette.chatre@intel.com, xiaoyao.li@intel.com, tony.lindgren@linux.intel.com, binbin.wu@linux.intel.com, isaku.yamahata@intel.com, yan.y.zhao@intel.com References: <20250703153712.155600-1-adrian.hunter@intel.com> <20250703153712.155600-3-adrian.hunter@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 7/6/25 20:16, Chao Gao wrote: > Even on a CPU w/ SEAM_NR and w/o X86_BUG_TDX_PW_MCE, is there still a risk of > poisoned memory being returned to the host kernel? Since only poison > consumption causes #MCE, if a poisoned page is never consumed in SEAM non-root > mode, there will be no #MCE, and the mentioned commit won't mark the page as > poisoned. > > A reclaimed poisoned page could be reused and potentially cause a kernel panic. > While WBINVD could help, we believe it's not worth it as it will slow down the > vast majority of cases. Is my understanding correct? How is this any different from any other kind of hardware poison? Why should this specific kind of freeing (TDX private memory being freed back to the host) operation be different from any other kind of free?