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 A5D7CC54E4A for ; Fri, 8 Mar 2024 18:18:42 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 2ECFB6B03E1; Fri, 8 Mar 2024 13:18:42 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 29C7F6B03E3; Fri, 8 Mar 2024 13:18:42 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 13E046B03E4; Fri, 8 Mar 2024 13:18:42 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0017.hostedemail.com [216.40.44.17]) by kanga.kvack.org (Postfix) with ESMTP id 00F006B03E1 for ; Fri, 8 Mar 2024 13:18:41 -0500 (EST) Received: from smtpin09.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay01.hostedemail.com (Postfix) with ESMTP id A35E11C154B for ; Fri, 8 Mar 2024 18:18:41 +0000 (UTC) X-FDA: 81874682442.09.D687ED5 Received: from mgamail.intel.com (mgamail.intel.com [192.198.163.18]) by imf27.hostedemail.com (Postfix) with ESMTP id 63F6740019 for ; Fri, 8 Mar 2024 18:18:39 +0000 (UTC) Authentication-Results: imf27.hostedemail.com; dkim=pass header.d=intel.com header.s=Intel header.b=GZ2XbqJ0; spf=none (imf27.hostedemail.com: domain of kirill.shutemov@linux.intel.com has no SPF policy when checking 192.198.163.18) smtp.mailfrom=kirill.shutemov@linux.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=1709921919; 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: in-reply-to:in-reply-to:references:references:dkim-signature; bh=euuaqR7XP0WQNICctTeLr64RmC/siYlYS+WHt6RZvVU=; b=W+DFGjlbzw3+SbomBzZKzURqIyRFNjAclLtHQSIKckeQZP4JB70prryCBhcUf0t4HhOgGf 9pGoFBoYHxAH9YIKD0jR/3AgyWV2swzeTKWYHmiiSDyyqATs+GHcD1N2BCtANlUlaHBWuT V/9coArAQEDpjtrCXtri5oenaFTIXjQ= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1709921919; a=rsa-sha256; cv=none; b=KXN6NfpWMo2xLO8rblCuF7etUo/qud7KnaQUMGKxTHsxQMxdX14rtwsBUWjhlXgBDWNdFA MngMI4kAEgGFCmGXAoQP85l/hR5DpbpXWMY32HZ10XrPQpvcLNAV46xsuz2r8hKfLjghut c/UqzQe7CExdwCp2g6taqJm4c2r0PJE= ARC-Authentication-Results: i=1; imf27.hostedemail.com; dkim=pass header.d=intel.com header.s=Intel header.b=GZ2XbqJ0; spf=none (imf27.hostedemail.com: domain of kirill.shutemov@linux.intel.com has no SPF policy when checking 192.198.163.18) smtp.mailfrom=kirill.shutemov@linux.intel.com; dmarc=pass (policy=none) header.from=intel.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1709921919; x=1741457919; h=date:from:to:cc:subject:message-id:references: mime-version:in-reply-to; bh=gq7+JjRtDe8WuE7Xt3z4Svy36SZ/wWjmXmaR0mY39+I=; b=GZ2XbqJ0ucoP2dAD/Z8GVd5Qbk/ssP8/dVIQBdu0ZLCBjJUmpJzcn9Qf blQei7k8E7YrRvihdbH6D69GVDSw1tj3BhNFohI1eElwuLGL947rA/O+H w4q05m50cAVfubq+iQAzpXUoR0ickmr2zkxBC7i1T/k3wYCjUlQYyb6N/ dmIzBoUBVcV6nTOz0ah9MbPSF+y9e8me0ATLUnynDdR7Be4+YPi9knHEy ExqeY3VXFcNPXB2+sW8KkVruOW9WberYAc3DYnh+7umoyRdtDkVmqWg4z p3P2VrIxYRWah1YgvkPYuMuJnaPdiFuY1LNbiqSl1Ps/wzA5ttayb6i09 Q==; X-IronPort-AV: E=McAfee;i="6600,9927,11007"; a="4497597" X-IronPort-AV: E=Sophos;i="6.07,110,1708416000"; d="scan'208";a="4497597" Received: from fmsmga001.fm.intel.com ([10.253.24.23]) by fmvoesa112.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 08 Mar 2024 10:18:33 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6600,9927,11007"; a="937047748" X-IronPort-AV: E=Sophos;i="6.07,110,1708416000"; d="scan'208";a="937047748" Received: from black.fi.intel.com ([10.237.72.28]) by fmsmga001.fm.intel.com with ESMTP; 08 Mar 2024 10:18:29 -0800 Received: by black.fi.intel.com (Postfix, from userid 1000) id 9D04D1F1; Fri, 8 Mar 2024 20:18:28 +0200 (EET) Date: Fri, 8 Mar 2024 20:18:28 +0200 From: "Kirill A. Shutemov" To: Dave Hansen Cc: Andy Lutomirski , Yosry Ahmed , Andrew Morton , Thomas Gleixner , Ingo Molnar , Borislav Petkov , "Peter Zijlstra (Intel)" , the arch/x86 maintainers , linux-mm@kvack.org, Linux Kernel Mailing List Subject: Re: [RFC PATCH 2/3] x86/mm: make sure LAM is up-to-date during context switching Message-ID: References: <20240307133916.3782068-1-yosryahmed@google.com> <20240307133916.3782068-3-yosryahmed@google.com> <420fcb06-c3c3-4e8f-a82d-be2fb2ef444d@app.fastmail.com> <35b670e2-9ef5-4d3a-b6ea-f8016dfa088d@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <35b670e2-9ef5-4d3a-b6ea-f8016dfa088d@intel.com> X-Rspamd-Queue-Id: 63F6740019 X-Rspam-User: X-Stat-Signature: 4jchb8tzm37144unwo3zagbzbabug9pa X-Rspamd-Server: rspam03 X-HE-Tag: 1709921919-569559 X-HE-Meta: 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 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: List-Subscribe: List-Unsubscribe: On Fri, Mar 08, 2024 at 07:23:58AM -0800, Dave Hansen wrote: > On 3/7/24 17:34, Andy Lutomirski wrote: > >> Fix this by making sure we write a new CR3 if LAM is not > >> up-to-date. No problems were observed in practice, this was found > >> by code inspection. > > I think it should be fixed with a much bigger hammer: explicit IPIs. > > Just don't ever let it get out of date, like install_ldt(). > I guess it matters whether the thing that matters is having a persistent > inconsistency or a temporary one. IPIs will definitely turn a permanent > one into a temporary one. > > But this is all easier to reason about if we can get rid of even the > temporary inconsistency. > > Wouldn't this be even simpler than IPIs? > > static inline unsigned long set_tlbstate_lam_mode(struct mm_struct *mm) > { > unsigned long lam = READ_ONCE(mm->context.lam_cr3_mask); > > + /* LAM is for userspace only. Ignore it for kernel threads: */ > + if (tsk->flags & PF_KTHREAD) > + return 0; I like this approach. kthread_use_mm() WARNs if it called for non-PF_KTHREAD task, so it should be okay. I was worried that it would also exclude io_uring, but worker threads don't have the flag set. -- Kiryl Shutsemau / Kirill A. Shutemov