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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id AF836C43217 for ; Mon, 7 Nov 2022 18:02:52 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 0776E8E0003; Mon, 7 Nov 2022 13:02:52 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 027C58E0001; Mon, 7 Nov 2022 13:02:51 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id E31448E0003; Mon, 7 Nov 2022 13:02:51 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0010.hostedemail.com [216.40.44.10]) by kanga.kvack.org (Postfix) with ESMTP id D06F58E0001 for ; Mon, 7 Nov 2022 13:02:51 -0500 (EST) Received: from smtpin09.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay06.hostedemail.com (Postfix) with ESMTP id 8AE18AA9D4 for ; Mon, 7 Nov 2022 18:02:51 +0000 (UTC) X-FDA: 80107416942.09.B1897DF Received: from mga18.intel.com (mga18.intel.com [134.134.136.126]) by imf07.hostedemail.com (Postfix) with ESMTP id A0EDD4001B for ; Mon, 7 Nov 2022 18:02:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1667844170; x=1699380170; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=fDIy9GNTqYrRaEubc/ZHCrZPmxPfpeXIk3PMc/Gyqec=; b=J3gODAcec1g3NY/hLC7B/GdAp1ccYYhKivm16yXi8pVnkS1/XJvsByC4 Qpv3uxFTa6VuVoGmqOJXLrupVXLj47qvIZJppAQlA9zb/qn1xtNZt8FsS q2YrEjP92UHLveBlxQGLFU1ce6IoajmiwY+CBObnxn7cUTqKxvJFEQixM 0ckQ86dsIzEfyFhiCYM0PbxS+dFKtVlLu1VdsWIAtBULVEbO+c10b0fgu VOs8+hRb85raiKQHXkIrfIHhShVROdXVJaMoLGD5xFfkF88vcPyRqzKAu KFu/27vKBX3klLOLjCxNTu/wb/G+YI6z6FUbVZaHGn7Bt4WipBp11pzs8 g==; X-IronPort-AV: E=McAfee;i="6500,9779,10524"; a="293848589" X-IronPort-AV: E=Sophos;i="5.96,145,1665471600"; d="scan'208";a="293848589" Received: from fmsmga002.fm.intel.com ([10.253.24.26]) by orsmga106.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 07 Nov 2022 10:02:49 -0800 X-IronPort-AV: E=McAfee;i="6500,9779,10524"; a="741598319" X-IronPort-AV: E=Sophos;i="5.96,145,1665471600"; d="scan'208";a="741598319" Received: from peggykes-mobl.amr.corp.intel.com (HELO [10.251.7.244]) ([10.251.7.244]) by fmsmga002-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 07 Nov 2022 10:02:47 -0800 Message-ID: Date: Mon, 7 Nov 2022 10:02:44 -0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.2.2 Subject: Re: [PATCHv11 04/16] x86/mm: Handle LAM on context switch Content-Language: en-US To: "Kirill A. Shutemov" , Andy Lutomirski Cc: "Kirill A. Shutemov" , Dave Hansen , Peter Zijlstra , x86@kernel.org, Kostya Serebryany , Andrey Ryabinin , Andrey Konovalov , Alexander Potapenko , Taras Madan , Dmitry Vyukov , "H . J . Lu" , Andi Kleen , Rick Edgecombe , Bharata B Rao , Jacob Pan , Ashok Raj , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20221025001722.17466-1-kirill.shutemov@linux.intel.com> <20221025001722.17466-5-kirill.shutemov@linux.intel.com> <20221107171419.k33qd4rz3tyfrovs@box.shutemov.name> From: Dave Hansen In-Reply-To: <20221107171419.k33qd4rz3tyfrovs@box.shutemov.name> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1667844170; a=rsa-sha256; cv=none; b=KFc+tSBsHMSisYFBju0WydCAlg8uypB5J7+KHgFUQFcvY7YuhQtyJa5QGRzkW9Xuvt2SQg 8IDyT0pLekU9+jx+cxltEDGKJ/khq2at4yHwT3g9pFPcj85YT7qucieeqTIA/WyaLZG6Wl BkAlrcsWippvizcdALpF7X640qSs98g= ARC-Authentication-Results: i=1; imf07.hostedemail.com; dkim=none ("invalid DKIM record") header.d=intel.com header.s=Intel header.b=J3gODAce; spf=pass (imf07.hostedemail.com: domain of dave.hansen@intel.com designates 134.134.136.126 as permitted sender) smtp.mailfrom=dave.hansen@intel.com; dmarc=pass (policy=none) header.from=intel.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1667844170; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=PF79h4dVzt8QKvyZ3V9HY+3qxNCjwAzPYDohnWph56g=; b=Wbt7g4qcEXNDDHQFsTkBlBNgScYWL9kWb6hRWvuM/cHA3K9VCDU7jHUPD/avQGXSJ7D5DJ 9RPqeGpr7zARo87jsLwgLsJQe+mlbarNvlIGjWkLhdIH6fzTCZcvod88AAi5yktT3DBZaX wPLFuDbSN1LDH7DiytTviB8CinQECiA= X-Stat-Signature: kfaimn1jsjts7ebtzm3eo86w73hg8hbj X-Rspam-User: Authentication-Results: imf07.hostedemail.com; dkim=none ("invalid DKIM record") header.d=intel.com header.s=Intel header.b=J3gODAce; spf=pass (imf07.hostedemail.com: domain of dave.hansen@intel.com designates 134.134.136.126 as permitted sender) smtp.mailfrom=dave.hansen@intel.com; dmarc=pass (policy=none) header.from=intel.com X-Rspamd-Queue-Id: A0EDD4001B X-Rspamd-Server: rspam09 X-HE-Tag: 1667844170-504319 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 11/7/22 09:14, Kirill A. Shutemov wrote: > --- a/arch/x86/mm/tlb.c > +++ b/arch/x86/mm/tlb.c > @@ -561,7 +561,15 @@ void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next, > if (real_prev == next) { > VM_WARN_ON(this_cpu_read(cpu_tlbstate.ctxs[prev_asid].ctx_id) != > next->context.ctx_id); > - VM_WARN_ON(prev_lam != new_lam); > + > + /* > + * 'prev_lam' does not necessary match 'new_lam' here. In case > + * of race with LAM enabling, the updated 'lam_cr3_mask' can be > + * been before LAM-enabling IPI kicks in. > + * > + * The race is harmless: it is okay to update CR3 with new LAM > + * mode. The IPI will rewrite CR3 shortly. > + */ So, let's do something like this in switch_mm_irqs_off(): /* Not actually switching mm's */ VM_WARN_ON(this_cpu_read(cpu_tlbstate.... /* * If this races with another thread that enables * lam, 'new_lam' might not match 'prev_lam'. */ Then, in enable_lam_func(), something like this: /* * Update CR3 to get LAM active on the CPU * * This might not actually need to update CR3 if a context * switch happened between updating 'lam_cr3_mask' and * running this IPI handler. Update it unconditionally for * simplicity. */ cr3 = __read_cr3(); cr3 &= ~(X86_CR3_LAM_U48 | X86_CR3_LAM_U57); cr3 |= lam_mask; write_cr3(cr3); set_tlbstate_cr3_lam_mask(lam_mask); I'd much rather get folks thinking about IPI races in the IPI handler rather than thinking about the IPI handler in the context switch path. It's kinda silly to be describing the occasional superfluous enable_lam_func() activity from switch_mm_irqs_off().