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 EF508C46CA1 for ; Mon, 18 Sep 2023 07:44:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240157AbjIRHny (ORCPT ); Mon, 18 Sep 2023 03:43:54 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52388 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S240434AbjIRHna (ORCPT ); Mon, 18 Sep 2023 03:43:30 -0400 Received: from mail-ed1-x52c.google.com (mail-ed1-x52c.google.com [IPv6:2a00:1450:4864:20::52c]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6923B10D5 for ; Mon, 18 Sep 2023 00:41:12 -0700 (PDT) Received: by mail-ed1-x52c.google.com with SMTP id 4fb4d7f45d1cf-522bd411679so5289453a12.0 for ; Mon, 18 Sep 2023 00:41:12 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1695022870; x=1695627670; darn=vger.kernel.org; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:sender:from:to:cc:subject:date:message-id :reply-to; bh=0ZHZZX2awisr882TDRE7yqEqi53EXQ6avmbEwdMqX9s=; b=NFBWrBWEUJzgExS+sD2gsB3h6enf+75j+0z2GkSnQ5qUHDT7UJTQIGWfJkJ3jYt7Iv oAQtdP6A5x7BA2vdGS94j3Xjr5SssZ4PCI7enARI+a3KTiV+naStuoYw5hlwByIWpiZO 2FZGHNMrh/Wzx7dnTQeDKbeQYumSPyJyWwC9Onl65KrjQsH+P571zRXt3Jp5Y8sHHr9q 5Bgi/khX6zuqXSEd5FGuFDyx+aiSC0973j458tXTpK8LPCHuSE1V5hEE4aCR6nHkKrEh lLEzYrB8LCcZw3X5CNqI7lu49xEQCxBkxYk1+CLVRmpDsr7P6gzzDYozydMizyfT6c2L Lkgw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1695022870; x=1695627670; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:sender:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=0ZHZZX2awisr882TDRE7yqEqi53EXQ6avmbEwdMqX9s=; b=psvH0wHQ3iJQmbwdDZl6I0/uy3BEObvaiGQKxrjs+2sdxnlAJnu/m9VJH1eCqZi1+c MNga6oQeNpq7vywmuYB++OHLDqry+U/GbXJcaNwY5PEyKEPk1653bHnylLSaQ9YOD3C6 pgQgIzwV1UGe2hsUMenbdDYC5Ye61zgGj3qg42PQra/HH7nQyIAjlYghwkYJPV3gdsCz imp/wkN23n7dBqEjaQsf4jQ/sHEPfJ4sUQu8Fp2GnGhJ75MSWidtliRoaPLUBC/6qqgP qpG12OszMnKrc3L1LWbt91hFDaLMElQKAgueXSLKKSb1GqKKecaA1SgDA0tp8pBBLk83 +htw== X-Gm-Message-State: AOJu0YwlTVv97vYPAUuk5ANn7V7RtI3uxhw8T4Sj8jhdp+tdqjybSduF megd5DZzUuMdX4ReLEQi1UgG8e1OAHA= X-Google-Smtp-Source: AGHT+IFaoUVQqyjQWuqkZT4VXInIKqT8gQTri7bRVUw3Z38fAe1T4fXEHlCaZlEZzxJaBQD+60CpiQ== X-Received: by 2002:a05:6512:3096:b0:4fe:1681:9377 with SMTP id z22-20020a056512309600b004fe16819377mr7580562lfd.44.1695022522580; Mon, 18 Sep 2023 00:35:22 -0700 (PDT) Received: from gmail.com (1F2EF265.nat.pool.telekom.hu. [31.46.242.101]) by smtp.gmail.com with ESMTPSA id 26-20020a05600c229a00b003fe17901fcdsm14424890wmf.32.2023.09.18.00.35.21 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 18 Sep 2023 00:35:21 -0700 (PDT) Sender: Ingo Molnar Date: Mon, 18 Sep 2023 09:35:19 +0200 From: Ingo Molnar To: Brendan Jackman , Andy Lutomirski , Thomas Gleixner Cc: luto@kernel.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, linux-kernel@vger.kernel.org, laijs@linux.alibaba.com, yosryahmed@google.com, reijiw@google.com, oweisse@google.com Subject: Re: [PATCH RESEND] x86/entry: Don't write to CR3 when restoring to kernel CR3 Message-ID: References: <20230817121513.1382800-1-jackmanb@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230817121513.1382800-1-jackmanb@google.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Brendan Jackman wrote: > From: Lai Jiangshan > > Skip resuming KERNEL pages since it is already KERNEL CR3 > > Signed-off-by: Lai Jiangshan > Signed-off-by: Brendan Jackman > --- > > While staring at paranoid_exit I was confused about why we had this CR3 > write, avoiding it seems like a free optimisation. The original commit > 21e94459110252 ("x86/mm: Optimize RESTORE_CR3") says "Most NMI/paranoid > exceptions will not in fact change pagetables" but I didn't't understand > what the "most" was referring to. I then discovered this patch on the > mailing list, Andy said[1] that it looks correct so maybe now is the > time to merge it? > > Note there's another patch in [1] as well, the benefit of that one is > not obvious to me though. > > We've tested an equivalent patch in our internal kernel. > > [1] https://lore.kernel.org/lkml/20200526043507.51977-3-laijs@linux.alibaba.com/ > -- >8 -- > arch/x86/entry/calling.h | 13 ++++--------- > 1 file changed, 4 insertions(+), 9 deletions(-) I concur that this is a good change, but it would be really nice to get an ack from Andy or Thomas as well. Thanks, Ingo