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X-CSE-ConnectionGUID: dtnMxFuwRAScZP4+bcJ28A== X-CSE-MsgGUID: IebsIY0tQU6R+kQJ3Yypqw== X-IronPort-AV: E=McAfee;i="6800,10657,11696"; a="75653232" X-IronPort-AV: E=Sophos;i="6.21,283,1763452800"; d="scan'208";a="75653232" Received: from fmviesa009.fm.intel.com ([10.60.135.149]) by fmvoesa106.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 09 Feb 2026 17:13:38 -0800 X-CSE-ConnectionGUID: tbbH5F5yRoSJKzoBMXZTog== X-CSE-MsgGUID: NQiT/0T8SNWVt0N4IOnUcw== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.21,283,1763452800"; d="scan'208";a="210996951" Received: from rchatre-mobl4.amr.corp.intel.com (HELO [10.125.108.24]) ([10.125.108.24]) by fmviesa009-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 09 Feb 2026 17:13:37 -0800 Message-ID: <3f31f8f8-b0a6-4ff9-b2ea-eeb04196b20a@intel.com> Date: Mon, 9 Feb 2026 17:13:36 -0800 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 v1] x86/smp: Set up exception handling before cr4_init() To: Sohil Mehta , Xin Li Cc: linux-kernel@vger.kernel.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, peterz@infradead.org, andrew.cooper3@citrix.com, nikunj@amd.com, thomas.lendacky@amd.com, seanjc@google.com, stable@vger.kernel.org References: <20260206185035.1250577-1-xin@zytor.com> <37de06e1-aae4-4ebd-ac93-1846ee4cd91e@intel.com> <52e152b9-c840-4480-9337-0f0aca327543@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 2/9/26 16:18, Sohil Mehta wrote: > > However, I found another location where we enable FRED in CR4 before > enabling the MSRs. > > __restore_processor_state(): > > ... > > __write_cr4(ctxt->cr4); > > ... > > if (ctxt->cr4 & X86_CR4_FRED) { > cpu_init_fred_exceptions(); > cpu_init_fred_rsps(); > } > > Due to limitations of my test platform, I couldn't verify the FRED print > in __restore_processor_state()'s path. But, could "restore" run into a > similar issue in the future? It sure looks like it. Good catch! I have the feeling there's never been an exception in that code anyway. The: wrmsrq(MSR_GS_BASE, ctxt->kernelmode_gs_base); is misplaced too. Exception handling leans heavily on MSR_GS_BASE. But, it doesn't hurt to be consistent about the ordering. In a perfect world, we'd probably unify all this code. Maybe the boot code establishes a 'saved_context' and all the APs just restore_processor_state() to go online normally instead of just for a restore. Or maybe the restore_processor_state() should be unified more with start_secondary() because a big chunk of the stuff its restoring is pretty static already. But there's no need today to do anything that drastic.