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=-10.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, 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 7CEC5C2D0E4 for ; Mon, 23 Nov 2020 14:23:19 +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 0CDC720758 for ; Mon, 23 Nov 2020 14:23:19 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="CgLtSWkL" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0CDC720758 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=arm.com 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=bRgcAB7mz/Hk9P6RGUx/RJhozaSfUceiyeWWlCS88EE=; b=CgLtSWkLzjYnRx0+DNZqiVJU4 LpSzrEwZmkwErMB5nGzvfeIjS43dJ7p7nJaXxJteGWL77VG7IkrjgkWuVV/K1bDVnqkoExCPl85GA oQg7LmWproHCT9o+714yb1LDUgwWPClU/junOP5upni4RbGXXCC+Wjane6Gid3ZUmRkcTPlUjahUl inW1jveaDQhLLwHmpEeweUSrXhOiDjxCjB2d3i4p1nb9xjDiv2M+hETmQIp8CQrf/tOJXCocEOTQt 882rZaxEHGUnwx633w5KjQUjZae/Gy1ULNeJPfcghyARINfYqg1FRHmdrO3w79OYF3oTM74ydPSt6 Y9WW9i1Kw==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1khCju-0005bh-DI; Mon, 23 Nov 2020 14:22:46 +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 1khCjr-0005af-9z for linux-arm-kernel@lists.infradead.org; Mon, 23 Nov 2020 14:22:44 +0000 Received: from gaia (unknown [95.146.230.165]) (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 8647E20782; Mon, 23 Nov 2020 14:22:40 +0000 (UTC) Date: Mon, 23 Nov 2020 14:22:37 +0000 From: Catalin Marinas To: Will Deacon Subject: Re: [PATCH 2/6] arm64: pgtable: Ensure dirty bit is preserved across pte_wrprotect() Message-ID: <20201123142237.GF17833@gaia> References: <20201120143557.6715-1-will@kernel.org> <20201120143557.6715-3-will@kernel.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20201120143557.6715-3-will@kernel.org> 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_092243_448421_E13C12D2 X-CRM114-Status: GOOD ( 19.52 ) 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: Yu Zhao , Anshuman Khandual , Peter Zijlstra , kernel-team@android.com, linux-kernel@vger.kernel.org, stable@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 02:35:53PM +0000, Will Deacon wrote: > With hardware dirty bit management, calling pte_wrprotect() on a writable, > dirty PTE will lose the dirty state and return a read-only, clean entry. My assumption at the time was that the caller of pte_wrprotect() already moved the 'dirty' information to the underlying page. Most pte_wrprotect() calls also do a pte_mkclean(). However, it doesn't seem to always be the case (soft-dirty but we don't support it yet). I was worried that we may inadvertently set the dirty bit when doing a pte_wrprotect() on a freshly created pte (not read from memory, for example __split_huge_pmd_locked()) but I think all our __P* and __S* attributes start with a PTE_RDONLY, therefore the pte_hw_dirty() returns false. A test for mm/debug_vm_pgtable.c, something like: for (i = 0, i < ARRAY_SIZE(protection_map); i++) { pte = pfn_pte(pfn, protection_map(i)); WARN_ON(pte_dirty(pte_wrprotect(pte)); } (I'll leave this to Anshuman ;)) > Move the logic from ptep_set_wrprotect() into pte_wrprotect() to ensure that > the dirty bit is preserved for writable entries, as this is required for > soft-dirty bit management if we enable it in the future. > > Cc: > Signed-off-by: Will Deacon I think this could go back as far as the hardware AF/DBM support (v4.3): Fixes: 2f4b829c625e ("arm64: Add support for hardware updates of the access and dirty pte bits") If you limit this fix to 4.14, you probably don't need additional commits. Otherwise, at least this one: 3bbf7157ac66 ("arm64: Convert pte handling from inline asm to using (cmp)xchg") and a slightly more intrusive: 73e86cb03cf2 ("arm64: Move PTE_RDONLY bit handling out of set_pte_at()") We also had some attempts at fixing ptep_set_wrprotect(): 64c26841b349 ("arm64: Ignore hardware dirty bit updates in ptep_set_wrprotect()") Fixed subsequently by: 8781bcbc5e69 ("arm64: mm: Fix pte_mkclean, pte_mkdirty semantics") I have a hope that at some point we'll understand how this all works ;). For this patch: Reviewed-by: Catalin Marinas _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel