From patchwork Fri Sep 21 15:34:05 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Steve Capper X-Patchwork-Id: 10610511 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 595F9913 for ; Fri, 21 Sep 2018 15:35:19 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 4746E2E47C for ; Fri, 21 Sep 2018 15:35:19 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 3A2302E4E2; Fri, 21 Sep 2018 15:35:19 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.8 required=2.0 tests=BAYES_00,DKIM_SIGNED, MAILING_LIST_MULTI,RCVD_IN_DNSWL_NONE,T_DKIM_INVALID autolearn=ham version=3.3.1 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.wl.linuxfoundation.org (Postfix) with ESMTPS id 62BFC2E4CE for ; Fri, 21 Sep 2018 15:35:18 +0000 (UTC) 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:MIME-Version:Cc:List-Subscribe: List-Help:List-Post:List-Archive:List-Unsubscribe:List-Id:References: In-Reply-To:Message-Id:Date:Subject:To:From:Reply-To:Content-ID: Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID:List-Owner; bh=K+nFPB/tU8nRja4tFtFJSNkxa6wBAwtQaUmEu922gs4=; b=Ahvq9Ko+rAWapUbT01hybPh1Ag +PY0D42loyY8cvmvTd9aVwCzknuD+pd6y2o0BHlf0jmXOrvlOJ2lYvEfinS60JrAe6cO57NJnqFKQ 51wOfCRJ1VLOqrOuaMxvAKGRvfgl0vnsgSADseVNTCU9/4vPAnYfz7h/Uupa/HKNXS24GBuzcoISf UvDVJVYXMpBMvlk3mOIsp4aebciUnsBCFjcy4sT59WWY34Wg4WeLmg4TfSR2PhvnCRzW+eE1j80r0 691ZpvjB3VC/lh3+RS9eKYULXQdTvi19uUKMEhXrqvg2N6ypYe+KEH8tTdzOwwUKtoFsY3NH6UgS9 YCB0uQRQ==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.90_1 #2 (Red Hat Linux)) id 1g3NSM-0005Pa-Ei; Fri, 21 Sep 2018 15:34:58 +0000 Received: from foss.arm.com ([217.140.101.70]) by bombadil.infradead.org with esmtp (Exim 4.90_1 #2 (Red Hat Linux)) id 1g3NRn-0005C8-G8 for linux-arm-kernel@lists.infradead.org; Fri, 21 Sep 2018 15:34:25 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id ABE5315AD; Fri, 21 Sep 2018 08:34:15 -0700 (PDT) Received: from capper-debian.emea.arm.com (usa-sjc-mx-foss1.foss.arm.com [217.140.101.70]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 615D23F557; Fri, 21 Sep 2018 08:34:15 -0700 (PDT) From: Steve Capper To: linux-arm-kernel@lists.infradead.org Subject: [PATCH V2 2/2] arm64: hugetlb: Avoid unnecessary clearing in huge_ptep_set_access_flags Date: Fri, 21 Sep 2018 16:34:05 +0100 Message-Id: <20180921153405.10090-3-steve.capper@arm.com> X-Mailer: git-send-email 2.11.0 In-Reply-To: <20180921153405.10090-1-steve.capper@arm.com> References: <20180921153405.10090-1-steve.capper@arm.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20180921_083423_570690_F841D245 X-CRM114-Status: GOOD ( 15.82 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: catalin.marinas@arm.com, Steve Capper , will.deacon@arm.com, zhang.lei@jp.fujitsu.com MIME-Version: 1.0 Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+patchwork-linux-arm=patchwork.kernel.org@lists.infradead.org X-Virus-Scanned: ClamAV using ClamSMTP For contiguous hugetlb, huge_ptep_set_access_flags performs a get_clear_flush (which then flushes the TLBs) even when no change of ptes is necessary. Unfortunately, this behaviour can lead to back-to-back page faults being generated when running with multiple threads that access the same contiguous huge page. Thread 1 | Thread 2 -----------------------------+------------------------------ hugetlb_fault | huge_ptep_set_access_flags | -> invalidate pte range | hugetlb_fault continue processing | wait for hugetlb_fault_mutex release mutex and return | huge_ptep_set_access_flags | -> invalidate pte range hugetlb_fault ... This patch changes huge_ptep_set_access_flags s.t. we first read the contiguous range of ptes (whilst preserving dirty information); the pte range is only then invalidated where necessary and this prevents further spurious page faults. Fixes: d8bdcff28764 ("arm64: hugetlb: Add break-before-make logic for contiguous entries") Reported-by: Lei Zhang Signed-off-by: Steve Capper --- Changed in v2: we just check dirty, young for the contiguous range and writable for the first pte in the range. --- arch/arm64/mm/hugetlbpage.c | 38 ++++++++++++++++++++++++++++++++++---- 1 file changed, 34 insertions(+), 4 deletions(-) diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c index f85be2f8b140..f58ea503ad01 100644 --- a/arch/arm64/mm/hugetlbpage.c +++ b/arch/arm64/mm/hugetlbpage.c @@ -323,11 +323,40 @@ pte_t huge_ptep_get_and_clear(struct mm_struct *mm, return get_clear_flush(mm, addr, ptep, pgsize, ncontig); } +/* + * huge_ptep_set_access_flags will update access flags (dirty, accesssed) + * and write permission. + * + * For a contiguous huge pte range we need to check whether or not write + * permission has to change only on the first pte in the set. Then for + * all the contiguous ptes we need to check whether or not there is a + * discrepancy between dirty or young. + */ +static int __cont_access_flags_changed(pte_t *ptep, pte_t pte, int ncontig) +{ + int i; + + if (pte_write(pte) != pte_write(huge_ptep_get(ptep))) + return 1; + + for (i = 0; i < ncontig; i++) { + pte_t orig_pte = huge_ptep_get(ptep + i); + + if (pte_dirty(pte) != pte_dirty(orig_pte)) + return 1; + + if (pte_young(pte) != pte_young(orig_pte)) + return 1; + } + + return 0; +} + int huge_ptep_set_access_flags(struct vm_area_struct *vma, unsigned long addr, pte_t *ptep, pte_t pte, int dirty) { - int ncontig, i, changed = 0; + int ncontig, i; size_t pgsize = 0; unsigned long pfn = pte_pfn(pte), dpfn; pgprot_t hugeprot; @@ -339,9 +368,10 @@ int huge_ptep_set_access_flags(struct vm_area_struct *vma, ncontig = find_num_contig(vma->vm_mm, addr, ptep, &pgsize); dpfn = pgsize >> PAGE_SHIFT; + if (!__cont_access_flags_changed(ptep, pte, ncontig)) + return 0; + orig_pte = get_clear_flush(vma->vm_mm, addr, ptep, pgsize, ncontig); - if (!pte_same(orig_pte, pte)) - changed = 1; /* Make sure we don't lose the dirty or young state */ if (pte_dirty(orig_pte)) @@ -354,7 +384,7 @@ int huge_ptep_set_access_flags(struct vm_area_struct *vma, for (i = 0; i < ncontig; i++, ptep++, addr += pgsize, pfn += dpfn) set_pte_at(vma->vm_mm, addr, ptep, pfn_pte(pfn, hugeprot)); - return changed; + return 1; } void huge_ptep_set_wrprotect(struct mm_struct *mm,