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X-CSE-ConnectionGUID: N85MEm+vQ02Oj4jwZDf6Eg== X-CSE-MsgGUID: SEdzg03rRhiUIeQebVWf4w== X-IronPort-AV: E=McAfee;i="6800,10657,11785"; a="79485644" X-IronPort-AV: E=Sophos;i="6.23,233,1770624000"; d="scan'208";a="79485644" Received: from fmviesa006.fm.intel.com ([10.60.135.146]) by fmvoesa111.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 13 May 2026 10:13:01 -0700 X-CSE-ConnectionGUID: VP1SdegsSZeflZ7dyAv+WA== X-CSE-MsgGUID: JPV5/kRdTa2jrqhkvaxlJQ== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.23,233,1770624000"; d="scan'208";a="233690384" Received: from cmdeoliv-mobl4.amr.corp.intel.com (HELO [10.125.108.49]) ([10.125.108.49]) by fmviesa006-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 13 May 2026 10:13:00 -0700 Message-ID: <669f925a-df4f-4497-ae41-46b08b6abce6@intel.com> Date: Wed, 13 May 2026 10:12:59 -0700 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] x86/entry: Read CR2 in asm entry stub to redcue NMI clobbering window To: Rik van Riel , Thomas Gleixner Cc: Ingo Molnar , Borislav Petkov , x86@kernel.org, linux-kernel@vger.kernel.org, kernel-team@meta.com, Dave Hansen , Andy Lutomirski , Xin Li References: <20260513121259.0aae7adc@fangorn> <1a39356971b5ba2c363ee47a80759595c8a69ecd.camel@surriel.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 5/13/26 09:43, Rik van Riel wrote: ... > I have only "seen" this in syzkaller, so I don't know > what the symptoms would look like if a regular system > hit this race window. > > I would not be surprised if we occasionally hit this > in production, but given that I don't know what the > symptoms would look like, I have no idea how often. I don't think there's a concrete enough problem being solved here to justify adding complexity to the entry code. Especially since it's not even a robust solution for the problem. The FRED thing is simple, robust, and doesn't affect the actual (nasty) entry assembly. I think we should do the FRED bits and continue to ignore the pre-FRED problem.