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=-8.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=ham 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 AE155C31E46 for ; Wed, 12 Jun 2019 05:04:37 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (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 69BC920866 for ; Wed, 12 Jun 2019 05:04:37 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 69BC920866 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=ellerman.id.au Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from lists.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 45NvtV4xLdzDqvd for ; Wed, 12 Jun 2019 15:04:34 +1000 (AEST) Received: from ozlabs.org (bilbo.ozlabs.org [203.11.71.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 45NvmH6xLGzDqsv for ; Wed, 12 Jun 2019 14:59:11 +1000 (AEST) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=ellerman.id.au Received: by ozlabs.org (Postfix, from userid 1034) id 45NvmH6CQKz9sDB; Wed, 12 Jun 2019 14:59:11 +1000 (AEST) X-powerpc-patch-notification: thanks X-powerpc-patch-commit: 33258a1db165cf43a9e6382587ad06e9b7f8187c X-Patchwork-Hint: ignore In-Reply-To: <20190607035636.5446-1-npiggin@gmail.com> To: Nicholas Piggin , linuxppc-dev@lists.ozlabs.org From: Michael Ellerman Subject: Re: [PATCH 1/2] powerpc/64s: Fix THP PMD collapse serialisation Message-Id: <45NvmH6CQKz9sDB@ozlabs.org> Date: Wed, 12 Jun 2019 14:59:11 +1000 (AEST) X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "Aneesh Kumar K . V" , Nicholas Piggin Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Fri, 2019-06-07 at 03:56:35 UTC, Nicholas Piggin wrote: > Commit 1b2443a547f9 ("powerpc/book3s64: Avoid multiple endian conversion > in pte helpers") changed the actual bitwise tests in pte_access_permitted > by using pte_write() and pte_present() helpers rather than raw bitwise > testing _PAGE_WRITE and _PAGE_PRESENT bits. > > The pte_present change now returns true for ptes which are !_PAGE_PRESENT > and _PAGE_INVALID, which is the combination used by pmdp_invalidate to > synchronize access from lock-free lookups. pte_access_permitted is used by > pmd_access_permitted, so allowing GUP lock free access to proceed with > such PTEs breaks this synchronisation. > > This bug has been observed on HPT host, with random crashes and corruption > in guests, usually together with bad PMD messages in the host. > > Fix this by adding an explicit check in pmd_access_permitted, and > documenting the condition explicitly. > > The pte_write() change should be okay, and would prevent GUP from falling > back to the slow path when encountering savedwrite ptes, which matches > what x86 (that does not implement savedwrite) does. > > Fixes: 1b2443a547f9 ("powerpc/book3s64: Avoid multiple endian conversion in pte helpers") > Cc: Aneesh Kumar K.V > Cc: Christophe Leroy > Signed-off-by: Nicholas Piggin > Reviewed-by: Aneesh Kumar K.V Applied to powerpc fixes, thanks. https://git.kernel.org/powerpc/c/33258a1db165cf43a9e6382587ad06e9 cheers