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=-2.3 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, 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 51E24C3A5A6 for ; Thu, 19 Sep 2019 15:00:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 158E921907 for ; Thu, 19 Sep 2019 15:00:12 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=shutemov-name.20150623.gappssmtp.com header.i=@shutemov-name.20150623.gappssmtp.com header.b="02D+wngb" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389795AbfISPAL (ORCPT ); Thu, 19 Sep 2019 11:00:11 -0400 Received: from mail-ed1-f68.google.com ([209.85.208.68]:41275 "EHLO mail-ed1-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387407AbfISPAL (ORCPT ); Thu, 19 Sep 2019 11:00:11 -0400 Received: by mail-ed1-f68.google.com with SMTP id f20so3477370edv.8 for ; Thu, 19 Sep 2019 08:00:09 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=shutemov-name.20150623.gappssmtp.com; s=20150623; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=rsy153zpl4yxoGCSq5N5IH86opdKnCHpMC3JulF2khA=; b=02D+wngbGXHZGUTd/OI3S4I3/pW/FS6cieICZCCkmbioDgm+zgBjOiH57lPnSWirfN +B4Feg8AmGwk7F+utHKC7GrdfJzUHKCJ4ajtySG8KxAouv6EvlG1yoqerF06hXnVcWwX TrHOQhOgYP9grvwP04SfPFkRbIDxj+NuVLs1X1zXVqDtLbxDjQS4pC2SXJhJs7ObyuVM 84MyFS80tqrbS4agYsvbwWVXwVHM/klMaBAKH+F+n4o1l5/a6xCmwxBcLGRO6bLWNKLD CeK3wIOS9gOxliCa8/h+Ka9CNuPH34azA0jVtIpCsVsr6Jne05lWZg1kpU+YucTZKd7W LCvg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=rsy153zpl4yxoGCSq5N5IH86opdKnCHpMC3JulF2khA=; b=XC4GcBcfXhN/QTd7tkz6nKPfqVzri+58us2Eo1IrKWJwK/hos7tleCfkvFCO16LuaM ZqAxMthhOjvzFLm3P8+0ETN9PWLXDrNlbCiz+u5Gwt/5cedkCHkZ7LNipPOdtGUcBMaF U+9f+EAmNRmjZxhu15wQJraiWADo5EaUp7+3QXmTZPP9KAT9ho4v8UDoLoXwMmdBxkMw uCCzukljKKijZ8OnbHYKrurAqwvtkLWT5DT7Yb+kz+TAqG7enTsSg7+27LXAKblMW5kG 27ePhKtYR6ZWTYARoPSmpzeWBP5z3xTMaEFfuD3snQOEqBnuR88POp86iVRY4d6s/7dD kbuQ== X-Gm-Message-State: APjAAAXDuUpeG9xujfoTQqvbciNB5WCTJirgiE86yPxIIN8TqxT8DnXG wV15oCO5H78HcbWOiZHtdajHmw== X-Google-Smtp-Source: APXvYqyx/AckV5APDHiZafOBx5pGNPnvX1/IDqUdyyu9pyklLZREADmTvqxKDNf7fmed54UHx0fVzA== X-Received: by 2002:a05:6402:1688:: with SMTP id a8mr7542905edv.225.1568905209039; Thu, 19 Sep 2019 08:00:09 -0700 (PDT) Received: from box.localdomain ([86.57.175.117]) by smtp.gmail.com with ESMTPSA id a22sm1039452ejs.17.2019.09.19.08.00.08 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 19 Sep 2019 08:00:08 -0700 (PDT) Received: by box.localdomain (Postfix, from userid 1000) id 8BBF3101F17; Thu, 19 Sep 2019 18:00:07 +0300 (+03) Date: Thu, 19 Sep 2019 18:00:07 +0300 From: "Kirill A. Shutemov" To: Catalin Marinas Cc: Jia He , Will Deacon , Mark Rutland , James Morse , Marc Zyngier , Matthew Wilcox , "Kirill A. Shutemov" , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Suzuki Poulose , Punit Agrawal , Anshuman Khandual , Jun Yao , Alex Van Brunt , Robin Murphy , Thomas Gleixner , Andrew Morton , =?utf-8?B?SsOpcsO0bWU=?= Glisse , Ralph Campbell , hejianet@gmail.com, Kaly Xin Subject: Re: [PATCH v4 3/3] mm: fix double page fault on arm64 if PTE_AF is cleared Message-ID: <20190919150007.k7scjplcya53j7r4@box> References: <20190918131914.38081-1-justin.he@arm.com> <20190918131914.38081-4-justin.he@arm.com> <20190918140027.ckj32xnryyyesc23@box> <20190918180029.GB20601@iMac.local> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190918180029.GB20601@iMac.local> User-Agent: NeoMutt/20180716 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Sep 18, 2019 at 07:00:30PM +0100, Catalin Marinas wrote: > On Wed, Sep 18, 2019 at 05:00:27PM +0300, Kirill A. Shutemov wrote: > > On Wed, Sep 18, 2019 at 09:19:14PM +0800, Jia He wrote: > > > @@ -2152,20 +2163,34 @@ static inline void cow_user_page(struct page *dst, struct page *src, unsigned lo > > > */ > > > if (unlikely(!src)) { > > > void *kaddr = kmap_atomic(dst); > > > - void __user *uaddr = (void __user *)(va & PAGE_MASK); > > > + void __user *uaddr = (void __user *)(addr & PAGE_MASK); > > > + pte_t entry; > > > > > > /* > > > * 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. On architectures with software "accessed" bits, > > > + * we would take a double page fault here, so mark it > > > + * accessed here. > > > */ > > > + if (arch_faults_on_old_pte() && !pte_young(vmf->orig_pte)) { > > > + spin_lock(vmf->ptl); > > > + if (likely(pte_same(*vmf->pte, vmf->orig_pte))) { > > > + entry = pte_mkyoung(vmf->orig_pte); > > > + if (ptep_set_access_flags(vma, addr, > > > + vmf->pte, entry, 0)) > > > + update_mmu_cache(vma, addr, vmf->pte); > > > + } > > > > I don't follow. > > > > So if pte has changed under you, you don't set the accessed bit, but never > > the less copy from the user. > > > > What makes you think it will not trigger the same problem? > > > > I think we need to make cow_user_page() fail in this case and caller -- > > wp_page_copy() -- return zero. If the fault was solved by other thread, we > > are fine. If not userspace would re-fault on the same address and we will > > handle the fault from the second attempt. > > It would be nice to clarify the semantics of this function and do as > you suggest but the current comment is slightly confusing: > > /* > * If the source page was a PFN mapping, we don't have > * a "struct page" for it. We do a best-effort copy by > * just copying from the original user address. If that > * fails, we just zero-fill it. Live with it. > */ > > Would any user-space rely on getting a zero-filled page here instead of > a recursive fault? I don't see the point in zero-filled page in this case. SIGBUS sounds like more appropriate response, no? -- Kirill A. Shutemov