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=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,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 5C9FBC4CEC4 for ; Mon, 23 Sep 2019 17:04:55 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 27A7F20820 for ; Mon, 23 Sep 2019 17:04:55 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="Z1gWOypu" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 27A7F20820 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=aaLy9Z/8yrO+2WS1UBQ25StCtbZAQNkDtFvsO6+lGeQ=; b=Z1gWOypu8B0DSw KTggtPtUYVSIHJvheanw+HP7o7HVORNdxkr+TbOr9Q4Ah115XcNZ/YDH0kmeJem1tX24+sFTk5f/y 25stlWwMv7fV/K1FKSnzfsKCJtkLuTmxIyesipcmthSFYcQErhoPeHtg2UH/VmKpj0yOsqVFS/4aE Mbj587O28ste/KjScPEr6YDTA3WyzWs1ev97RedZ0I8/BGh16fv1xTuAPagwXQ401Q5C1gx30z94c n/UKwWx8wgZgwoob4OFa4YGT0BJgT5MrJKZfIqG5netH8BptzKpVGtbZZ5kNmzz8ESu+dlRzxXR+t wlZM82Y47E79ayA3IUKw==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92.2 #3 (Red Hat Linux)) id 1iCRlV-00062z-7u; Mon, 23 Sep 2019 17:04:45 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.92.2 #3 (Red Hat Linux)) id 1iCRlQ-0005px-Bp for linux-arm-kernel@lists.infradead.org; Mon, 23 Sep 2019 17:04:42 +0000 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 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-Disposition: inline In-Reply-To: <20190921135054.142360-4-justin.he@arm.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190923_100440_684422_AE05A1FD X-CRM114-Status: GOOD ( 19.98 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Mark Rutland , Kaly Xin , Ralph Campbell , Andrew Morton , Suzuki Poulose , Marc Zyngier , Anshuman Khandual , linux-kernel@vger.kernel.org, Matthew Wilcox , linux-mm@kvack.org, =?iso-8859-1?B?Suly9G1l?= Glisse , James Morse , linux-arm-kernel@lists.infradead.org, Punit Agrawal , hejianet@gmail.com, Thomas Gleixner , nd@arm.com, Will Deacon , Alex Van Brunt , "Kirill A. Shutemov" , Robin Murphy Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.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 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel