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=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 895F9C432C1 for ; Tue, 24 Sep 2019 16:35:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 56EE820872 for ; Tue, 24 Sep 2019 16:35:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390185AbfIXQfs (ORCPT ); Tue, 24 Sep 2019 12:35:48 -0400 Received: from foss.arm.com ([217.140.110.172]:33480 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388942AbfIXQfs (ORCPT ); Tue, 24 Sep 2019 12:35:48 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 5589A142F; Tue, 24 Sep 2019 09:35:47 -0700 (PDT) Received: from arrakis.emea.arm.com (arrakis.cambridge.arm.com [10.1.196.78]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id A49143F694; Tue, 24 Sep 2019 09:35:44 -0700 (PDT) Date: Tue, 24 Sep 2019 17:35:42 +0100 From: Catalin Marinas To: Jia He 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 , =?iso-8859-1?B?Suly9G1l?= Glisse , Ralph Campbell , "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: <20190924163542.GI41214@arrakis.emea.arm.com> 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> <6267b685-5162-85ac-087f-112303bb7035@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <6267b685-5162-85ac-087f-112303bb7035@gmail.com> User-Agent: Mutt/1.10.1 (2018-07-13) 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 11:29:07PM +0800, Jia He wrote: > On 2019/9/24 18:33, 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: > > > > > /* > > > > > * 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". > > I am not 100% sure that I understand your suggestion well, so I > drafted the patch Well, however you think the code is cleaner really. The copy/paste didn't work well, tabs disappeared (or rather the Exchange server corrupting outgoing emails) but I'll try to comment below: > -static inline void cow_user_page(struct page *dst, struct page *src, > unsigned long va, struct vm_area_struct *vma) > +static inline bool cow_user_page(struct page *dst, struct page *src, > +                 struct vm_fault *vmf) >  { > +    struct vm_area_struct *vma = vmf->vma; > +    struct mm_struct *mm = vma->vm_mm; > +    unsigned long addr = vmf->address; > +    bool ret; > +    pte_t entry; > +    void *kaddr; > +    void __user *uaddr; > + >      debug_dma_assert_idle(src); > > +    if (likely(src)) { > +        copy_user_highpage(dst, src, addr, vma); > +        return true; > +    } > + >      /* >       * 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. >       */ > -    if (unlikely(!src)) { > -        void *kaddr = kmap_atomic(dst); > -        void __user *uaddr = (void __user *)(va & PAGE_MASK); > +    kaddr = kmap_atomic(dst); > +    uaddr = (void __user *)(addr & PAGE_MASK); > + > +    /* > +     * On architectures with software "accessed" bits, we would > +     * take a double page fault, so mark it accessed here. > +     */ > +    vmf->pte = pte_offset_map_lock(mm, vmf->pmd, addr, &vmf->ptl); > +    if (arch_faults_on_old_pte() && !pte_young(vmf->orig_pte)) { I'd move the pte_offset_map_lock() inside the 'if' block as we don't want to affect architectures that handle old ptes automatically. > +        if (!likely(pte_same(*vmf->pte, vmf->orig_pte))) { > +            /* > +             * 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. > +             */ > +            ret = false; > +            goto pte_unlock; > +        } > + > +        entry = pte_mkyoung(vmf->orig_pte); > +        if (ptep_set_access_flags(vma, addr, vmf->pte, entry, 0)) > +            update_mmu_cache(vma, addr, vmf->pte); > +    } > > +    /* > +     * 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)) { >          /* > -         * 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. > +         * Give a warn in case there can be some obscure > +         * use-case >           */ > -        if (__copy_from_user_inatomic(kaddr, uaddr, PAGE_SIZE)) > -            clear_page(kaddr); > -        kunmap_atomic(kaddr); > -        flush_dcache_page(dst); > -    } else > -        copy_user_highpage(dst, src, va, vma); > +        WARN_ON_ONCE(1); > +        clear_page(kaddr); > +    } > + > +    ret = true; > + > +pte_unlock: > +    pte_unmap_unlock(vmf->pte, vmf->ptl); Since the locking would be moved in the 'if' block above, we need another check here before unlocking: if (arch_faults_on_old_pte() && !pte_young(vmf->orig_pte)) pte_unmap_unlock(vmf->pte, vmf->ptl); You could probably replace the two calls to arch_faults_on_old_pte() with a single bool variable initialisation, something like: force_mkyoung = arch_faults_on_old_pte() && !pte_young(vmf->orig_pte) and only check for "if (force_mkyoung)" in both cases. > +    kunmap_atomic(kaddr); > +    flush_dcache_page(dst); > + > +    return ret; >  } -- Catalin