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 4AA7AC4CECF for ; Mon, 23 Sep 2019 17:04:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 21EDE2168B for ; Mon, 23 Sep 2019 17:04:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2439949AbfIWREk (ORCPT ); Mon, 23 Sep 2019 13:04:40 -0400 Received: from foss.arm.com ([217.140.110.172]:45666 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732522AbfIWREk (ORCPT ); Mon, 23 Sep 2019 13:04:40 -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 2EBAE1000; Mon, 23 Sep 2019 10:04:39 -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 7E0523F67D; Mon, 23 Sep 2019 10:04:36 -0700 (PDT) Date: Mon, 23 Sep 2019 18:04:34 +0100 From: Catalin Marinas To: Jia He Cc: 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 , hejianet@gmail.com, Kaly Xin , nd@arm.com Subject: Re: [PATCH v8 3/3] mm: fix double page fault on arm64 if PTE_AF is cleared Message-ID: <20190923170433.GE10192@arrakis.emea.arm.com> References: <20190921135054.142360-1-justin.he@arm.com> <20190921135054.142360-4-justin.he@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190921135054.142360-4-justin.he@arm.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 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. > + */ Nitpick: please follow the kernel coding style for multi-line comments (above and the for the rest of the patch): /* * Your multi-line comment. */ > + 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); > + } Another nit, you could rewrite this block slightly to avoid too much indentation. Something like (untested): if (arch_faults_on_old_pte() && !pte_young(vmf->orig_pte)) { vmf->pte = pte_offset_map_lock(mm, vmf->pmd, addr, &vmf->ptl); if (unlikely(!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. */ pte_unmap_unlock(vmf->pte, vmf->ptl); return false; } entry = pte_mkyoung(vmf->orig_pte); if (ptep_set_access_flags(vma, addr, vmf->pte, entry, 0)) update_mmu_cache(vma, addr, vmf->pte); 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. > /* > * 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. > clear_page(kaddr); > + } > kunmap_atomic(kaddr); > flush_dcache_page(dst); > } else > - copy_user_highpage(dst, src, va, vma); > + copy_user_highpage(dst, src, addr, vma); > + > + return true; > } -- Catalin