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=-2.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no 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 800ADC43331 for ; Fri, 6 Sep 2019 14:57:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4AA432082C for ; Fri, 6 Sep 2019 14:57:53 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="OoJLwlcF" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2392196AbfIFO5w (ORCPT ); Fri, 6 Sep 2019 10:57:52 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:52506 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726019AbfIFO5v (ORCPT ); Fri, 6 Sep 2019 10:57:51 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=8uK72fUcoR/dOk67AIhDl3phYWTEBOSNQgXr2opx6YQ=; b=OoJLwlcFoMcbFlWhKHZL0Iv2t xGSzljJBjV7GRPPUygW13XZxQrWrvjLCjMUwNZW1LKX0QBQ/7xZEL5PN+q9J0HdZjEWQZnB1tw+QA /yGOWMjkyadvtPvYE/i3REW8kTAdxbBkXW++18U4vW2fZEKZkfY0jAQMz79K+9ZagWBVKrEeNFTjZ 8pPK5z1TpoluFgMEjSdLdJJlJerF+SffUw/gVMsURZvjv/PbcVSU1u8Q53JMAu4ldpzE7c/cnfxN4 pD/nYxN6XMpI9wEUPWYoyhHn8LvediGThCGX7hpHY8aVNvnFA/fQK0YLj65WvTI/X8geljykGhl7S PzGWja24w==; Received: from willy by bombadil.infradead.org with local (Exim 4.92 #3 (Red Hat Linux)) id 1i6FgE-0001Sx-K1; Fri, 06 Sep 2019 14:57:42 +0000 Date: Fri, 6 Sep 2019 07:57:42 -0700 From: Matthew Wilcox To: Jia He Cc: Andrew Morton , =?iso-8859-1?B?Suly9G1l?= Glisse , Ralph Campbell , Jason Gunthorpe , Peter Zijlstra , Dave Airlie , "Aneesh Kumar K.V" , Thomas Hellstrom , Souptick Joarder , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Catalin Marinas Subject: Re: [PATCH v2] mm: fix double page fault on arm64 if PTE_AF is cleared Message-ID: <20190906145742.GX29434@bombadil.infradead.org> References: <20190906135747.211836-1-justin.he@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190906135747.211836-1-justin.he@arm.com> User-Agent: Mutt/1.11.4 (2019-03-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Sep 06, 2019 at 09:57:47PM +0800, Jia He wrote: > * This really shouldn't fail, because the page is there > * in the page tables. But it might just be unreadable, > * in which case we just give up and fill the result with > - * zeroes. > + * zeroes. If PTE_AF is cleared on arm64, it might > + * cause double page fault. So makes pte young here How about: * zeroes. On architectures with software "accessed" bits, * we would take a double page fault here, so mark it * accessed here. > */ > + if (!pte_young(vmf->orig_pte)) { Let's guard this with: if (arch_sw_access_bit && !pte_young(vmf->orig_pte)) { #define arch_sw_access_bit 0 by default and have arm64 override it (either to a variable or a constant ... your choice). Also, please somebody decide on a better name than arch_sw_access_bit. > + entry = pte_mkyoung(vmf->orig_pte); > + if (ptep_set_access_flags(vmf->vma, vmf->address, > + vmf->pte, entry, 0)) This indentation is wrong; it makes vmf->pte look like part of the subsequent statement instead of part of the condition. > + update_mmu_cache(vmf->vma, vmf->address, > + vmf->pte); > + } > +