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=DKIMWL_WL_HIGH,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 EB540C432C1 for ; Tue, 24 Sep 2019 10:33:47 +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 B135820872 for ; Tue, 24 Sep 2019 10:33:47 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="L1QKrVly" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B135820872 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=QLKvopYHS1rF2QIKLnRyJpmk0ErZewV53S+WuMLtxPI=; b=L1QKrVlyakAM2M s2Uacj2I23ZZbNoXMTuQ4wiFX319PlnEXLUx2QK/g/LFVevtPdbe4zutWiPRya7bTh6o6eyFQEF/7 K/G7Y0nJjCcrQByLjEuDxcna9IiPmT/30nxMJrxUkdyfECwGrcJ8fjY44RtConYlblJIxAPAu5H7f 3OKnfDmJ0wfn8FVSX7QR/XjzEEgt2BPH9e3m1D5+iMqqNG+TpHx/DP2VDWP1TXmPaOzBzH0EyTZjw 9y87V5PosbEuI7nTUirVP4u7hth9x8CAZy2eFxmkMDB9bizmPBR+WcefdL4uO/SRJivieE9qKG6ps QwsiUiPgpGdEzHKYJKBw==; 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 1iCi8W-0002cu-4A; Tue, 24 Sep 2019 10:33:36 +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 1iCi8S-0002c8-Te for linux-arm-kernel@lists.infradead.org; Tue, 24 Sep 2019 10:33:34 +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 2B94C142F; Tue, 24 Sep 2019 03:33:30 -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 77BFE3F67D; Tue, 24 Sep 2019 03:33:27 -0700 (PDT) Date: Tue, 24 Sep 2019 11:33:25 +0100 From: Catalin Marinas To: "Justin He (Arm Technology China)" Subject: Re: [PATCH v8 3/3] mm: fix double page fault on arm64 if PTE_AF is cleared Message-ID: <20190924103324.GB41214@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> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: 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-20190924_033333_041580_7AB05018 X-CRM114-Status: GOOD ( 25.02 ) 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 \(Arm Technology China\)" , 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 , 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 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". -- Catalin _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel