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=-2.2 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 5FEAAC432C1 for ; Tue, 24 Sep 2019 11:59:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2A2BE21655 for ; Tue, 24 Sep 2019 11:59:18 +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="kzEdrK5K" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2504756AbfIXL7R (ORCPT ); Tue, 24 Sep 2019 07:59:17 -0400 Received: from mail-ed1-f68.google.com ([209.85.208.68]:37801 "EHLO mail-ed1-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388614AbfIXL7Q (ORCPT ); Tue, 24 Sep 2019 07:59:16 -0400 Received: by mail-ed1-f68.google.com with SMTP id r4so1577689edy.4 for ; Tue, 24 Sep 2019 04:59:13 -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=yfQkKYdmCnwP8GQDgvukKfhrIz/ARlVTMjl+vdxLN6c=; b=kzEdrK5KGIj08/JrZaz8ci6yj9t/++4d8rPavj45ueJFdJnWlcvcyYaB9yXFzNq1s7 0dklLEr6JucXgsFCgpSAkAFPz41EaQevI/b4nzl96v3QRXNPxXKHHI0SkRwaJpLnksee El9UuJAKUOUVmCIdYXeenQzTr7JEFbSV8qfF3gAS/OyomlySVvlHsAzBeJYGrqKy8QN0 yDF44Ru/+H0sXp/w9OjFg4+EFTjuB1AwthMG1aoT3+fEN6PN5uuTIkT0ThZJWnpms4XM qHSyTHNQi9831Ltqc0s3+HNvEtr0x8iU7FlXykNOVwZ25p8Qnp++bxWaTBo7dm4VRZuB HtSg== 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=yfQkKYdmCnwP8GQDgvukKfhrIz/ARlVTMjl+vdxLN6c=; b=DvckHdwERKoXT6hLYtLTZHGbHxzZnuo9hx5j4z/xkNmWzUY1E4F+WKY3vdbrag4d8A MxslLp9CfhcQSw9H1VtQWisFVqgqyj6xqe8URTtCzn2RPFEhqhGTVas9xTM6CPrgfjwU gIAxVSKCwJaJfKgpCuDWxjqOXixbWv6FIHVbADr+GIGJkVk1o8XuheoQhf3zScTKfNQ/ u9j2sIfrspfPjkGL3s6G+XnvMlaObn4NBjw0N0u3OmCiVVqFF9s9rPkGC9Wtr8GeEkEA 0u1WRDizU0DKEJpsYEAyALpsiCr2v5bd93r2U3TVI7xKc82ufEt1ZuK3H5TG2hxOOEdE RsZw== X-Gm-Message-State: APjAAAUEcLMwt8vVwoYkZJ9zF4wqhSrMSkNXy16FC2UsPMe+a6PBLwyE QjwtES8hPCkC+vGyQatYDfrs1A== X-Google-Smtp-Source: APXvYqywWn8dGPH0MFvcwZjCOlr8PR0mjKnlZh5uuaMJO79gEAj4kKuFC9SRjmQzB0N/ONkPZRk9KQ== X-Received: by 2002:a17:906:860d:: with SMTP id o13mr2037274ejx.284.1569326353237; Tue, 24 Sep 2019 04:59:13 -0700 (PDT) Received: from box.localdomain ([86.57.175.117]) by smtp.gmail.com with ESMTPSA id ci8sm188286ejb.71.2019.09.24.04.59.12 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 24 Sep 2019 04:59:12 -0700 (PDT) Received: by box.localdomain (Postfix, from userid 1000) id AD8A41022A6; Tue, 24 Sep 2019 14:59:13 +0300 (+03) Date: Tue, 24 Sep 2019 14:59:13 +0300 From: "Kirill A. Shutemov" To: Catalin Marinas Cc: "Justin He (Arm Technology China)" , 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 , Alex Van Brunt , Robin Murphy , Thomas Gleixner , Andrew Morton , =?utf-8?B?SsOpcsO0bWU=?= Glisse , Ralph Campbell , "hejianet@gmail.com" , "Kaly Xin (Arm Technology China)" , nd Subject: Re: [PATCH v8 3/3] mm: fix double page fault on arm64 if PTE_AF is cleared Message-ID: <20190924115913.ju67nr4gcdbzbeva@box> References: <20190921135054.142360-1-justin.he@arm.com> <20190921135054.142360-4-justin.he@arm.com> <20190923170433.GE10192@arrakis.emea.arm.com> <20190924103324.GB41214@arrakis.emea.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190924103324.GB41214@arrakis.emea.arm.com> User-Agent: NeoMutt/20180716 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Sep 24, 2019 at 11:33:25AM +0100, Catalin Marinas wrote: > On Tue, Sep 24, 2019 at 06:43:06AM +0000, Justin He (Arm Technology China) wrote: > > Catalin Marinas wrote: > > > On Sat, Sep 21, 2019 at 09:50:54PM +0800, Jia He wrote: > > > > @@ -2151,21 +2163,53 @@ static inline void cow_user_page(struct page *dst, struct page *src, unsigned lo > > > > * fails, we just zero-fill it. Live with it. > > > > */ > > > > if (unlikely(!src)) { > > > > - void *kaddr = kmap_atomic(dst); > > > > - void __user *uaddr = (void __user *)(va & PAGE_MASK); > > > > + void *kaddr; > > > > + pte_t entry; > > > > + void __user *uaddr = (void __user *)(addr & PAGE_MASK); > > > > > > > > + /* On architectures with software "accessed" bits, we would > > > > + * take a double page fault, so mark it accessed here. > > > > + */ > [...] > > > > + if (arch_faults_on_old_pte() && !pte_young(vmf->orig_pte)) { > > > > + vmf->pte = pte_offset_map_lock(mm, vmf->pmd, addr, > > > > + &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); > > > > + } else { > > > > + /* Other thread has already handled the fault > > > > + * and we don't need to do anything. If it's > > > > + * not the case, the fault will be triggered > > > > + * again on the same address. > > > > + */ > > > > + pte_unmap_unlock(vmf->pte, vmf->ptl); > > > > + return false; > > > > + } > > > > + pte_unmap_unlock(vmf->pte, vmf->ptl); > > > > + } > [...] > > > > + > > > > + kaddr = kmap_atomic(dst); > > > > > > Since you moved the kmap_atomic() here, could the above > > > arch_faults_on_old_pte() run in a preemptible context? I suggested to > > > add a WARN_ON in patch 2 to be sure. > > > > Should I move kmap_atomic back to the original line? Thus, we can make sure > > that arch_faults_on_old_pte() is in the context of preempt_disabled? > > Otherwise, arch_faults_on_old_pte() may cause plenty of warning if I add > > a WARN_ON in arch_faults_on_old_pte. I tested it when I enable the PREEMPT=y > > on a ThunderX2 qemu guest. > > So we have two options here: > > 1. Change arch_faults_on_old_pte() scope to the whole system rather than > just the current CPU. You'd have to wire up a new arm64 capability > for the access flag but this way we don't care whether it's > preemptible or not. > > 2. Keep the arch_faults_on_old_pte() per-CPU but make sure we are not > preempted here. The kmap_atomic() move would do but you'd have to > kunmap_atomic() before the return. > > I think the answer to my question below also has some implication on > which option to pick: > > > > > /* > > > > * 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. > > > > */ > > > > - if (__copy_from_user_inatomic(kaddr, uaddr, PAGE_SIZE)) > > > > + if (__copy_from_user_inatomic(kaddr, uaddr, PAGE_SIZE)) { > > > > + /* Give a warn in case there can be some obscure > > > > + * use-case > > > > + */ > > > > + WARN_ON_ONCE(1); > > > > > > That's more of a question for the mm guys: at this point we do the > > > copying with the ptl released; is there anything else that could have > > > made the pte old in the meantime? I think unuse_pte() is only called on > > > anonymous vmas, so it shouldn't be the case here. > > If we need to hold the ptl here, you could as well have an enclosing > kmap/kunmap_atomic (option 2) with some goto instead of "return false". Yeah, look like we need to hold ptl for longer. There is nothing I see that would prevent clearing young bit under us otherwise. -- Kirill A. Shutemov