From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8D1F9C678D6 for ; Tue, 10 Jan 2023 13:43:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233412AbjAJNmq (ORCPT ); Tue, 10 Jan 2023 08:42:46 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38086 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232706AbjAJNmP (ORCPT ); Tue, 10 Jan 2023 08:42:15 -0500 Received: from szxga01-in.huawei.com (szxga01-in.huawei.com [45.249.212.187]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 65AEA8FC1 for ; Tue, 10 Jan 2023 05:42:14 -0800 (PST) Received: from kwepemi500024.china.huawei.com (unknown [172.30.72.54]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4NrsLX6g8KzqV3Z; Tue, 10 Jan 2023 21:37:24 +0800 (CST) Received: from [10.174.179.163] (10.174.179.163) by kwepemi500024.china.huawei.com (7.221.188.100) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.34; Tue, 10 Jan 2023 21:42:09 +0800 Message-ID: <8fd825e3-494a-8a06-2b30-91458db2815b@huawei.com> Date: Tue, 10 Jan 2023 21:42:08 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.1.2 Subject: Re: [PATCH -v2] x86/boot/compressed: Register dummy NMI handler in EFI boot loader, to avoid kdump crashes Content-Language: en-US To: Borislav Petkov CC: Ingo Molnar , , , , , , , , , , , , , References: <20230110102745.2514694-1-zengheng4@huawei.com> <684a2472-f388-b2e1-4a7a-7bc9a07650b4@huawei.com> From: Zeng Heng In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.179.163] X-ClientProxiedBy: dggems706-chm.china.huawei.com (10.3.19.183) To kwepemi500024.china.huawei.com (7.221.188.100) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2023/1/10 20:57, Borislav Petkov wrote: > On Tue, Jan 10, 2023 at 08:32:07PM +0800, Zeng Heng wrote: >> mce is registered on NMI handler by inject_init(). > That's a handler for the NMI raised by raise_mce(). That's for the injection > case, which is simulated. If you're fixing the injection case, then surely not > with a bogus boot NMI handler. OK, mce-injection is the simulated one. > >> Yes, exactly. The following procedure is like: >> >> panic() -> relocate_kernel() -> identity_mapped() -> x86 purgatory image -> >> EFI loader -> secondary kernel > I'm doubtful now as you're injecting errors so you're not really in #MC context > but in this contrived context which is actually an NMI one. So we need to think > about how to fix this case. > > Certainly not with an empty NMI handler... > > Regardless, we should do > > diff --git a/arch/x86/kernel/cpu/mce/core.c b/arch/x86/kernel/cpu/mce/core.c > index 7832a69d170e..57fe376ed049 100644 > --- a/arch/x86/kernel/cpu/mce/core.c > +++ b/arch/x86/kernel/cpu/mce/core.c > @@ -286,6 +286,8 @@ static noinstr void mce_panic(const char *msg, struct mce *final, char *exp) > if (!fake_panic) { > if (panic_timeout == 0) > panic_timeout = mca_cfg.panic_timeout; > + > + mce_wrmsrl(MSR_IA32_MCG_STATUS, 0); > panic(msg); > } else > pr_emerg(HW_ERR "Fake kernel panic: %s\n", msg); > > so that we not run kexec in #MC context. > > Hmmm. I don't have ready test case for real MCE to verify whether it has exited #MC context before panic() or not. In mce-inject case that based on NMI, it doesn't work as mentioned indeed. B.R., Zeng Heng