From patchwork Mon Aug 13 14:57:54 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Marc Zyngier X-Patchwork-Id: 10564471 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 9E1281390 for ; Mon, 13 Aug 2018 15:53:27 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 8C16129012 for ; Mon, 13 Aug 2018 15:53:27 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 7B755290DC; Mon, 13 Aug 2018 15:53:27 +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=-2.9 required=2.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,MAILING_LIST_MULTI autolearn=unavailable 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 2371229012 for ; Mon, 13 Aug 2018 15:53:27 +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=J5EwzyPsLm/6d59IRT421U/rYx2HezF+W/aFyji5TEI=; b=jvHtFTKrYxBawDug3EOeHxy9DF 7cyX833drr4HU+vsz37kXLQWVHCkGHV+oN86czCzKaNfLkj5oZGoDCBo8OgbSPqXLeO3UcTdP8fPr Ua+XzgqhYHdC7vBwmkOFfRkESajA0qZgegERAG2xQBEvUPH7ZrTdAHLIyCnRf7C4Bg4IG9z1kzrgL eNuedlZ2ApaWuRAFc96aaBIuLaK4Ee+4yfu9nwPApIVHLEVdzZYY6jeMMeZrYm3P4C6y3Tob4tOwX uRFgRVLnJ6HV2cWDnjmzd91o8p91TW3KUmB4pjcvi6yU7tCQ6bb/EnQsb1klUbPUPhclDPMcgwqH4 ir9fy/gw==; 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 1fpF9l-0007oC-9j; Mon, 13 Aug 2018 15:53:21 +0000 Received: from merlin.infradead.org ([2001:8b0:10b:1231::1]) by bombadil.infradead.org with esmtps (Exim 4.90_1 #2 (Red Hat Linux)) id 1fpF9c-0007eD-RC for linux-arm-kernel@bombadil.infradead.org; Mon, 13 Aug 2018 15:53:12 +0000 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=References:In-Reply-To:Message-Id:Date: Subject:Cc:To:From:Sender:Reply-To:MIME-Version:Content-Type: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=AwVc3XsdmijI4RBPIUSgQAAbZXKMUp5bOQxolEjwSpk=; b=ozFsiZ1KFVvBroytD5dv6q/mk GRFHS3TXcH7N3zWxaWoBH0dCv235SKCeygXvwVxVbRCgbOc9YWuw1G/KhfBCwQS68EIainYg83/OL ORsdtXqShThp4fUJRB3aOUVh4LrqnGDiYtl0BA84BDT8BR2EK8NF2PdpNhLhhqF3bof7nW5Khiktf JcWyP56peRKjtiJq/IUkPHdLs6fkrknKdKnY4Afdnwivlw7gj8m4vb78WvwUvAuoWpwudeCLPj9Yc UCJ1otPuBcCsYqRrHZ5T5QOYTX/oSk46Ah9vK/3PbSgCyT/psUC5VxfD1wRVIPnC1MgpdxzwL4NjS GTmwXmYcw==; Received: from foss.arm.com ([217.140.101.70]) by merlin.infradead.org with esmtp (Exim 4.90_1 #2 (Red Hat Linux)) id 1fpEL1-0004dp-Nk for linux-arm-kernel@lists.infradead.org; Mon, 13 Aug 2018 15:00:57 +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 10BBB168F; Mon, 13 Aug 2018 08:00:45 -0700 (PDT) Received: from approximate.Emea.Arm.com (approximate.Emea.Arm.com [10.4.13.119]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 1EA543F5D0; Mon, 13 Aug 2018 08:00:41 -0700 (PDT) From: Marc Zyngier To: Paolo Bonzini , =?utf-8?b?UmFkaW0gS3LEjW3DocWZ?= Subject: [PATCH 36/37] KVM: arm/arm64: Skip updating PMD entry if no change Date: Mon, 13 Aug 2018 15:57:54 +0100 Message-Id: <20180813145755.16566-37-marc.zyngier@arm.com> X-Mailer: git-send-email 2.18.0 In-Reply-To: <20180813145755.16566-1-marc.zyngier@arm.com> References: <20180813145755.16566-1-marc.zyngier@arm.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20180813_110055_982365_262C1605 X-CRM114-Status: GOOD ( 19.70 ) 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: Mark Rutland , Andrew Jones , Kees Cook , kvm@vger.kernel.org, "Gustavo A . R . Silva" , Andre Przywara , Punit Agrawal , Christoffer Dall , Dongjiu Geng , Jia He , Eric Auger , James Morse , Catalin Marinas , Suzuki Poulose , kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org 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 From: Punit Agrawal Contention on updating a PMD entry by a large number of vcpus can lead to duplicate work when handling stage 2 page faults. As the page table update follows the break-before-make requirement of the architecture, it can lead to repeated refaults due to clearing the entry and flushing the tlbs. This problem is more likely when - * there are large number of vcpus * the mapping is large block mapping such as when using PMD hugepages (512MB) with 64k pages. Fix this by skipping the page table update if there is no change in the entry being updated. Cc: stable@vger.kernel.org Fixes: ad361f093c1e ("KVM: ARM: Support hugetlbfs backed huge pages") Reviewed-by: Suzuki Poulose Acked-by: Christoffer Dall Signed-off-by: Punit Agrawal Signed-off-by: Marc Zyngier --- virt/kvm/arm/mmu.c | 38 +++++++++++++++++++++++++++----------- 1 file changed, 27 insertions(+), 11 deletions(-) diff --git a/virt/kvm/arm/mmu.c b/virt/kvm/arm/mmu.c index 97d27cd9c654..13dfe36501aa 100644 --- a/virt/kvm/arm/mmu.c +++ b/virt/kvm/arm/mmu.c @@ -1044,19 +1044,35 @@ static int stage2_set_pmd_huge(struct kvm *kvm, struct kvm_mmu_memory_cache pmd = stage2_get_pmd(kvm, cache, addr); VM_BUG_ON(!pmd); - /* - * Mapping in huge pages should only happen through a fault. If a - * page is merged into a transparent huge page, the individual - * subpages of that huge page should be unmapped through MMU - * notifiers before we get here. - * - * Merging of CompoundPages is not supported; they should become - * splitting first, unmapped, merged, and mapped back in on-demand. - */ - VM_BUG_ON(pmd_present(*pmd) && pmd_pfn(*pmd) != pmd_pfn(*new_pmd)); - old_pmd = *pmd; if (pmd_present(old_pmd)) { + /* + * Multiple vcpus faulting on the same PMD entry, can + * lead to them sequentially updating the PMD with the + * same value. Following the break-before-make + * (pmd_clear() followed by tlb_flush()) process can + * hinder forward progress due to refaults generated + * on missing translations. + * + * Skip updating the page table if the entry is + * unchanged. + */ + if (pmd_val(old_pmd) == pmd_val(*new_pmd)) + return 0; + + /* + * Mapping in huge pages should only happen through a + * fault. If a page is merged into a transparent huge + * page, the individual subpages of that huge page + * should be unmapped through MMU notifiers before we + * get here. + * + * Merging of CompoundPages is not supported; they + * should become splitting first, unmapped, merged, + * and mapped back in on-demand. + */ + VM_BUG_ON(pmd_pfn(old_pmd) != pmd_pfn(*new_pmd)); + pmd_clear(pmd); kvm_tlb_flush_vmid_ipa(kvm, addr); } else {