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 X-Spam-Level: X-Spam-Status: No, score=-15.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C295CC2D0E4 for ; Mon, 23 Nov 2020 18:37:12 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 412982078E for ; Mon, 23 Nov 2020 18:37:12 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="hQm4fGsP"; dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="rJRxc3FT" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 412982078E Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References:Message-ID: Subject:To:From:Date:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=UilmgurU9P0/uUoOEFAfwd/Dcw0kVGeq6uxe4JNHTqw=; b=hQm4fGsPwgFwYO7uWTuoiuF3U 8bQI3bfsEqk5tQV8SyVgx+54fejm16xEJAP74+Gu5QyWtltoApLnyop7G79S4W3fft8js3FMvcxRJ VLjDJWQHMxHC8Q+6EP1lpE0Vh+4Lc4nFl+sAPqyKhxOMs2VBjrkLWTvDrILGn3Xubms7whmcZtbuq SWHYIx036vDffzhtHlf3ED9K1jd4+0p/0HRYbEUZWGfoWxz2CP0R2rZxPZ8uEFebn8OUkuWQ5hGJJ oxf30YJDBsfBQ3XKFBVbRAw46I8peyr6ewCrv2v7F/pRXkHsDAEZjFDoBxQITDPyTLZLVngSAda5G B1FPFQPIw==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1khGh3-0004cy-Fs; Mon, 23 Nov 2020 18:36:05 +0000 Received: from mail.kernel.org ([198.145.29.99]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1khGh0-0004bh-H9 for linux-arm-kernel@lists.infradead.org; Mon, 23 Nov 2020 18:36:03 +0000 Received: from willie-the-truck (236.31.169.217.in-addr.arpa [217.169.31.236]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id D5DA12078E; Mon, 23 Nov 2020 18:35:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1606156560; bh=FZugMw/Hog6jEeQy+QszK3Ewi0gPdbcIiChWPVuppDo=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=rJRxc3FThC4AXXQDGd4ySKR1IZkIlI7DzUiFQldSiKAjLI2HAtTPmK5MPZKOrorz3 x1Zh1MdqtAPgOUgE9Ho3vR7dQq6ZnDBqCFbwg77D/fnnUal1k6Max/JTL8kr9GuTdx Ot2iTXuZ80JCwSsItHl9ALlh1HQ7kpo2oU0A8L04= Date: Mon, 23 Nov 2020 18:35:55 +0000 From: Will Deacon To: Yu Zhao Subject: Re: [PATCH 6/6] mm: proc: Avoid fullmm flush for young/dirty bit toggling Message-ID: <20201123183554.GC11688@willie-the-truck> References: <20201120143557.6715-1-will@kernel.org> <20201120143557.6715-7-will@kernel.org> <20201120204005.GC1303870@google.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20201120204005.GC1303870@google.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20201123_133602_752989_9608B42F X-CRM114-Status: GOOD ( 25.47 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: kernel-team@android.com, Anshuman Khandual , Peter Zijlstra , Catalin Marinas , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Minchan Kim , Linus Torvalds , linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Fri, Nov 20, 2020 at 01:40:05PM -0700, Yu Zhao wrote: > On Fri, Nov 20, 2020 at 02:35:57PM +0000, Will Deacon wrote: > > clear_refs_write() uses the 'fullmm' API for invalidating TLBs after > > updating the page-tables for the current mm. However, since the mm is not > > being freed, this can result in stale TLB entries on architectures which > > elide 'fullmm' invalidation. > > > > Ensure that TLB invalidation is performed after updating soft-dirty > > entries via clear_refs_write() by using the non-fullmm API to MMU gather. > > > > Signed-off-by: Will Deacon > > --- > > fs/proc/task_mmu.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c > > index a76d339b5754..316af047f1aa 100644 > > --- a/fs/proc/task_mmu.c > > +++ b/fs/proc/task_mmu.c > > @@ -1238,7 +1238,7 @@ static ssize_t clear_refs_write(struct file *file, const char __user *buf, > > count = -EINTR; > > goto out_mm; > > } > > - tlb_gather_mmu_fullmm(&tlb, mm); > > + tlb_gather_mmu(&tlb, mm, 0, TASK_SIZE); > > Let's assume my reply to patch 4 is wrong, and therefore we still need > tlb_gather/finish_mmu() here. But then wouldn't this change deprive > architectures other than ARM the opportunity to optimize based on the > fact it's a full-mm flush? Only for the soft-dirty case, but I think TLB invalidation is required there because we are write-protecting the entries and I don't see any mechanism to handle lazy invalidation for that (compared with the aging case, which is handled via pte_accessible()). Furthermore, If we decide that we can relax the TLB invalidation requirements here, then I'd much rather than was done deliberately, rather than as an accidental side-effect of another commit (since I think the current behaviour was a consequence of 7a30df49f63a). > It seems to me ARM's interpretation of tlb->fullmm is a special case, > not the other way around. Although I agree that this is subtle and error-prone (which is why I'm trying to make the API more explicit here), it _is_ documented clearly in asm-generic/tlb.h: * - mmu_gather::fullmm * * A flag set by tlb_gather_mmu() to indicate we're going to free * the entire mm; this allows a number of optimizations. * * - We can ignore tlb_{start,end}_vma(); because we don't * care about ranges. Everything will be shot down. * * - (RISC) architectures that use ASIDs can cycle to a new ASID * and delay the invalidation until ASID space runs out. Will _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel