From patchwork Thu Sep 29 11:37:01 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Will Deacon X-Patchwork-Id: 9356377 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id 56322600C8 for ; Thu, 29 Sep 2016 11:39:18 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 32B942996F for ; Thu, 29 Sep 2016 11:39:18 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 26F4529971; Thu, 29 Sep 2016 11:39:18 +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=-4.2 required=2.0 tests=BAYES_00, RCVD_IN_DNSWL_MED autolearn=ham version=3.3.1 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.9]) (using TLSv1.2 with cipher AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.wl.linuxfoundation.org (Postfix) with ESMTPS id D9D442996F for ; Thu, 29 Sep 2016 11:39:16 +0000 (UTC) Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.85_2 #1 (Red Hat Linux)) id 1bpZeW-00055j-Mw; Thu, 29 Sep 2016 11:37:24 +0000 Received: from foss.arm.com ([217.140.101.70]) by bombadil.infradead.org with esmtp (Exim 4.85_2 #1 (Red Hat Linux)) id 1bpZeS-00054R-7O for linux-arm-kernel@lists.infradead.org; Thu, 29 Sep 2016 11:37:21 +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 1651314; Thu, 29 Sep 2016 04:36:58 -0700 (PDT) Received: from edgewater-inn.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.72.51.249]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id D49963F3D6; Thu, 29 Sep 2016 04:36:57 -0700 (PDT) Received: by edgewater-inn.cambridge.arm.com (Postfix, from userid 1000) id A2A0E1AE0CBE; Thu, 29 Sep 2016 12:37:02 +0100 (BST) From: Will Deacon To: linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu Subject: [PATCH] arm64: KVM: Take S1 walks into account when determining S2 write faults Date: Thu, 29 Sep 2016 12:37:01 +0100 Message-Id: <1475149021-13288-1-git-send-email-will.deacon@arm.com> X-Mailer: git-send-email 2.1.4 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20160929_043720_273799_64115898 X-CRM114-Status: GOOD ( 11.62 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.20 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Marc Zyngier , Julien Grall , Will Deacon , Christoffer Dall 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 The WnR bit in the HSR/ESR_EL2 indicates whether a data abort was generated by a read or a write instruction. For stage 2 data aborts generated by a stage 1 translation table walk (i.e. the actual page table access faults at EL2), the WnR bit therefore reports whether the instruction generating the walk was a load or a store, *not* whether the page table walker was reading or writing the entry. For page tables marked as read-only at stage 2 (e.g. due to KSM merging them with the tables from another guest), this could result in livelock, where a page table walk generated by a load instruction attempts to set the access flag in the stage 1 descriptor, but fails to trigger CoW in the host since only a read fault is reported. This patch modifies the arm64 kvm_vcpu_dabt_iswrite function to take into account stage 2 faults in stage 1 walks. Since DBM cannot be disabled at EL2 for CPUs that implement it, we assume that these faults are always causes by writes, avoiding the livelock situation at the expense of occasional, spurious CoWs. We could, in theory, do a bit better by checking the guest TCR configuration and inspecting the page table to see why the PTE faulted. However, I doubt this is measurable in practice, and the threat of livelock is real. Cc: Marc Zyngier Cc: Christoffer Dall Cc: Julien Grall Signed-off-by: Will Deacon Reviewed-by: Marc Zyngier Reviewed-by: Christoffer Dall --- arch/arm64/include/asm/kvm_emulate.h | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-) diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h index 4cdeae3b17c6..948a9a8a9297 100644 --- a/arch/arm64/include/asm/kvm_emulate.h +++ b/arch/arm64/include/asm/kvm_emulate.h @@ -167,11 +167,6 @@ static inline bool kvm_vcpu_dabt_isvalid(const struct kvm_vcpu *vcpu) return !!(kvm_vcpu_get_hsr(vcpu) & ESR_ELx_ISV); } -static inline bool kvm_vcpu_dabt_iswrite(const struct kvm_vcpu *vcpu) -{ - return !!(kvm_vcpu_get_hsr(vcpu) & ESR_ELx_WNR); -} - static inline bool kvm_vcpu_dabt_issext(const struct kvm_vcpu *vcpu) { return !!(kvm_vcpu_get_hsr(vcpu) & ESR_ELx_SSE); @@ -192,6 +187,12 @@ static inline bool kvm_vcpu_dabt_iss1tw(const struct kvm_vcpu *vcpu) return !!(kvm_vcpu_get_hsr(vcpu) & ESR_ELx_S1PTW); } +static inline bool kvm_vcpu_dabt_iswrite(const struct kvm_vcpu *vcpu) +{ + return !!(kvm_vcpu_get_hsr(vcpu) & ESR_ELx_WNR) || + kvm_vcpu_dabt_iss1tw(vcpu); /* AF/DBM update */ +} + static inline bool kvm_vcpu_dabt_is_cm(const struct kvm_vcpu *vcpu) { return !!(kvm_vcpu_get_hsr(vcpu) & ESR_ELx_CM);