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y17mr897782pfl.204.1576644818062; Tue, 17 Dec 2019 20:53:38 -0800 (PST) Received: from [10.61.2.175] ([122.99.82.10]) by smtp.gmail.com with ESMTPSA id i127sm928216pfe.54.2019.12.17.20.53.34 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 17 Dec 2019 20:53:37 -0800 (PST) Subject: Re: [PATCH 1/1] kvm/book3s_64: Fixes crash caused by not cleaning vhost IOTLB To: Leonardo Bras , Paul Mackerras , Benjamin Herrenschmidt , Michael Ellerman Cc: kvm-ppc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, farosas@linux.ibm.com, David Gibson References: <20191217210658.73144-1-leonardo@linux.ibm.com> From: Alexey Kardashevskiy Autocrypt: addr=aik@ozlabs.ru; keydata= mQINBE+rT0sBEADFEI2UtPRsLLvnRf+tI9nA8T91+jDK3NLkqV+2DKHkTGPP5qzDZpRSH6mD EePO1JqpVuIow/wGud9xaPA5uvuVgRS1q7RU8otD+7VLDFzPRiRE4Jfr2CW89Ox6BF+q5ZPV /pS4v4G9eOrw1v09lEKHB9WtiBVhhxKK1LnUjPEH3ifkOkgW7jFfoYgTdtB3XaXVgYnNPDFo PTBYsJy+wr89XfyHr2Ev7BB3Xaf7qICXdBF8MEVY8t/UFsesg4wFWOuzCfqxFmKEaPDZlTuR 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c7E5M+/NpslPCmYnDjs5qg0/3ihh6XuOGggZQOqrYPC3PnsNs3NxirwOkVPQgO6mXxpuifvJ DG9EMkK8IBXnLulqVk54kf7fE0jT/d8RTtJIA92GzsgdK2rpT1MBKKVffjRFGwN7nQVOzi4T XrB5p+6ML7Bd84xOEGsj/vdaXmz1esuH7BOZAGEZfLRCHJ0GVCSssg== Message-ID: Date: Wed, 18 Dec 2019 15:53:32 +1100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.3.0 MIME-Version: 1.0 In-Reply-To: <20191217210658.73144-1-leonardo@linux.ibm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 18/12/2019 08:06, Leonardo Bras wrote: > Fixes a bug that happens when a virtual machine is created without DDW, > with vhost supporting a virtio-net device. > > In this scenario, an IOMMU with 32-bit DMA window will possibly map > IOVA's to different memory addresses. > > As the code works today, H_STUFF_TCE hypercall will be dealt only with > kvm code, which does not invalidate the IOTLB entry in vhost, meaning > that at some point, and old entry can cause an access to a previous > memory address that IOVA pointed. > > Example: > - virtio-net passes IOVA N to vhost, which point to M1 > - vhost tries IOTLB, but miss > - vhost translates IOVA N and stores result to IOTLB > - vhost writes to M1 > - (some IOMMU usage) > - virtio-net passes IOVA N to vhost, which now points to M2 > - vhost tries IOTLB, and translates IOVA N to M1 > - vhost writes to M1 > > The reason why this error was not so evident, is probably because the > IOTLB was small enough to almost always miss at the point an IOVA was > reused. Raising the IOTLB size to 32k (which is a module parameter that > defaults to 2k) is enough to reproduce the bug in +90% of the runs. > It usually takes less than 10 seconds of netperf to cause this bug > to happen. > > A few minutes after reproducing this bug, the guest usually crash. > > Fixing this bug involves cleaning a IOVA entry from IOTLB. > The guest kernel trigger this by doing a H_STUFF_TCE hypercall with > tce_value == 0. > > This change fixes this bug by returning H_TOO_HARD on kvmppc_h_stuff_tce > when tce_value == 0, which causes kvm to let qemu deal with this. > In this case, qemu does free the vhost IOTLB entry, which fixes the bug. > > Signed-off-by: Leonardo Bras > --- > arch/powerpc/kvm/book3s_64_vio.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/arch/powerpc/kvm/book3s_64_vio.c b/arch/powerpc/kvm/book3s_64_vio.c > index 883a66e76638..841eff3f6392 100644 > --- a/arch/powerpc/kvm/book3s_64_vio.c > +++ b/arch/powerpc/kvm/book3s_64_vio.c > @@ -710,6 +710,9 @@ long kvmppc_h_stuff_tce(struct kvm_vcpu *vcpu, > if (ret != H_SUCCESS) > return ret; > > + if (tce_value == 0) H_STUFF_TCE is always called with 0. Well, may be some AIX somewhere calls it with a value other than zero, and I probably saw some other value somewhere but in QEMU/KVM case it is 0 so you effectively disable in-kernel acceleration of H_STUFF_TCE which is undesirable. For now we should disable in-kernel H_STUFF_TCE/... handlers in QEMU just like we do for VFIO for older host kernels: https://git.qemu.org/?p=qemu.git;a=blob;f=hw/ppc/spapr_iommu.c;h=3d3bcc86496a5277d62f7855fbb09c013c015f27;hb=HEAD#l208 I am not sure what a proper solution would be, something like an eventfd and KVM's kvmppc_h_stuff_tce() signalling vhost that the latter needs to invalidate iotlbs. Or we can just say that we do not allow KVM acceleration if there is vhost+iommu on the same liobn (== vPHB, pretty much). Thanks, > + return H_TOO_HARD; > + > /* Check permission bits only to allow userspace poison TCE for debug */ > if (tce_value & (TCE_PCI_WRITE | TCE_PCI_READ)) > return H_PARAMETER; > -- Alexey 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=-13.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable 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 C9ABFC43603 for ; Wed, 18 Dec 2019 04:55:50 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org 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X2tXyeBixa3i/6dWJ4nIp3vGQicQkut1YBwR7dJq67/FCV3Mlj94jI0myHT5PIrCS2S8LtWX ikTJSxWUKmh7OP5mrqhwNe0ezgGiWxxvyNwThOHc5JvpzJLd32VDFilbxgu4Hhnf6LcgZJ2c Zd44XWqUu7FzVOYaSgIvTP0hNrBYm/E6M7yrLbs3JY74fGzPWGRbBUHTZXQEqQnZglXaVB5V ZhSFtHopZnBSCUSNDbB+QGy4B/E++Bb02IBTGl/JxmOwG+kZUnymsPvTtnNIeTLHxN/H/ae0 c7E5M+/NpslPCmYnDjs5qg0/3ihh6XuOGggZQOqrYPC3PnsNs3NxirwOkVPQgO6mXxpuifvJ DG9EMkK8IBXnLulqVk54kf7fE0jT/d8RTtJIA92GzsgdK2rpT1MBKKVffjRFGwN7nQVOzi4T XrB5p+6ML7Bd84xOEGsj/vdaXmz1esuH7BOZAGEZfLRCHJ0GVCSssg== Message-ID: Date: Wed, 18 Dec 2019 15:53:32 +1100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.3.0 MIME-Version: 1.0 In-Reply-To: <20191217210658.73144-1-leonardo@linux.ibm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: David Gibson , linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, kvm-ppc@vger.kernel.org, farosas@linux.ibm.com Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On 18/12/2019 08:06, Leonardo Bras wrote: > Fixes a bug that happens when a virtual machine is created without DDW, > with vhost supporting a virtio-net device. > > In this scenario, an IOMMU with 32-bit DMA window will possibly map > IOVA's to different memory addresses. > > As the code works today, H_STUFF_TCE hypercall will be dealt only with > kvm code, which does not invalidate the IOTLB entry in vhost, meaning > that at some point, and old entry can cause an access to a previous > memory address that IOVA pointed. > > Example: > - virtio-net passes IOVA N to vhost, which point to M1 > - vhost tries IOTLB, but miss > - vhost translates IOVA N and stores result to IOTLB > - vhost writes to M1 > - (some IOMMU usage) > - virtio-net passes IOVA N to vhost, which now points to M2 > - vhost tries IOTLB, and translates IOVA N to M1 > - vhost writes to M1 > > The reason why this error was not so evident, is probably because the > IOTLB was small enough to almost always miss at the point an IOVA was > reused. Raising the IOTLB size to 32k (which is a module parameter that > defaults to 2k) is enough to reproduce the bug in +90% of the runs. > It usually takes less than 10 seconds of netperf to cause this bug > to happen. > > A few minutes after reproducing this bug, the guest usually crash. > > Fixing this bug involves cleaning a IOVA entry from IOTLB. > The guest kernel trigger this by doing a H_STUFF_TCE hypercall with > tce_value == 0. > > This change fixes this bug by returning H_TOO_HARD on kvmppc_h_stuff_tce > when tce_value == 0, which causes kvm to let qemu deal with this. > In this case, qemu does free the vhost IOTLB entry, which fixes the bug. > > Signed-off-by: Leonardo Bras > --- > arch/powerpc/kvm/book3s_64_vio.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/arch/powerpc/kvm/book3s_64_vio.c b/arch/powerpc/kvm/book3s_64_vio.c > index 883a66e76638..841eff3f6392 100644 > --- a/arch/powerpc/kvm/book3s_64_vio.c > +++ b/arch/powerpc/kvm/book3s_64_vio.c > @@ -710,6 +710,9 @@ long kvmppc_h_stuff_tce(struct kvm_vcpu *vcpu, > if (ret != H_SUCCESS) > return ret; > > + if (tce_value == 0) H_STUFF_TCE is always called with 0. Well, may be some AIX somewhere calls it with a value other than zero, and I probably saw some other value somewhere but in QEMU/KVM case it is 0 so you effectively disable in-kernel acceleration of H_STUFF_TCE which is undesirable. For now we should disable in-kernel H_STUFF_TCE/... handlers in QEMU just like we do for VFIO for older host kernels: https://git.qemu.org/?p=qemu.git;a=blob;f=hw/ppc/spapr_iommu.c;h=3d3bcc86496a5277d62f7855fbb09c013c015f27;hb=HEAD#l208 I am not sure what a proper solution would be, something like an eventfd and KVM's kvmppc_h_stuff_tce() signalling vhost that the latter needs to invalidate iotlbs. Or we can just say that we do not allow KVM acceleration if there is vhost+iommu on the same liobn (== vPHB, pretty much). Thanks, > + return H_TOO_HARD; > + > /* Check permission bits only to allow userspace poison TCE for debug */ > if (tce_value & (TCE_PCI_WRITE | TCE_PCI_READ)) > return H_PARAMETER; > -- Alexey From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alexey Kardashevskiy Date: Wed, 18 Dec 2019 04:53:32 +0000 Subject: Re: [PATCH 1/1] kvm/book3s_64: Fixes crash caused by not cleaning vhost IOTLB Message-Id: List-Id: References: <20191217210658.73144-1-leonardo@linux.ibm.com> In-Reply-To: <20191217210658.73144-1-leonardo@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Leonardo Bras , Paul Mackerras , Benjamin Herrenschmidt , Michael Ellerman Cc: kvm-ppc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, farosas@linux.ibm.com, David Gibson On 18/12/2019 08:06, Leonardo Bras wrote: > Fixes a bug that happens when a virtual machine is created without DDW, > with vhost supporting a virtio-net device. > > In this scenario, an IOMMU with 32-bit DMA window will possibly map > IOVA's to different memory addresses. > > As the code works today, H_STUFF_TCE hypercall will be dealt only with > kvm code, which does not invalidate the IOTLB entry in vhost, meaning > that at some point, and old entry can cause an access to a previous > memory address that IOVA pointed. > > Example: > - virtio-net passes IOVA N to vhost, which point to M1 > - vhost tries IOTLB, but miss > - vhost translates IOVA N and stores result to IOTLB > - vhost writes to M1 > - (some IOMMU usage) > - virtio-net passes IOVA N to vhost, which now points to M2 > - vhost tries IOTLB, and translates IOVA N to M1 > - vhost writes to M1 > > The reason why this error was not so evident, is probably because the > IOTLB was small enough to almost always miss at the point an IOVA was > reused. Raising the IOTLB size to 32k (which is a module parameter that > defaults to 2k) is enough to reproduce the bug in +90% of the runs. > It usually takes less than 10 seconds of netperf to cause this bug > to happen. > > A few minutes after reproducing this bug, the guest usually crash. > > Fixing this bug involves cleaning a IOVA entry from IOTLB. > The guest kernel trigger this by doing a H_STUFF_TCE hypercall with > tce_value = 0. > > This change fixes this bug by returning H_TOO_HARD on kvmppc_h_stuff_tce > when tce_value = 0, which causes kvm to let qemu deal with this. > In this case, qemu does free the vhost IOTLB entry, which fixes the bug. > > Signed-off-by: Leonardo Bras > --- > arch/powerpc/kvm/book3s_64_vio.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/arch/powerpc/kvm/book3s_64_vio.c b/arch/powerpc/kvm/book3s_64_vio.c > index 883a66e76638..841eff3f6392 100644 > --- a/arch/powerpc/kvm/book3s_64_vio.c > +++ b/arch/powerpc/kvm/book3s_64_vio.c > @@ -710,6 +710,9 @@ long kvmppc_h_stuff_tce(struct kvm_vcpu *vcpu, > if (ret != H_SUCCESS) > return ret; > > + if (tce_value = 0) H_STUFF_TCE is always called with 0. Well, may be some AIX somewhere calls it with a value other than zero, and I probably saw some other value somewhere but in QEMU/KVM case it is 0 so you effectively disable in-kernel acceleration of H_STUFF_TCE which is undesirable. For now we should disable in-kernel H_STUFF_TCE/... handlers in QEMU just like we do for VFIO for older host kernels: https://git.qemu.org/?p=qemu.git;a=blob;f=hw/ppc/spapr_iommu.c;h=3bcc86496a5277d62f7855fbb09c013c015f27;hb=HEAD#l208 I am not sure what a proper solution would be, something like an eventfd and KVM's kvmppc_h_stuff_tce() signalling vhost that the latter needs to invalidate iotlbs. Or we can just say that we do not allow KVM acceleration if there is vhost+iommu on the same liobn (= vPHB, pretty much). Thanks, > + return H_TOO_HARD; > + > /* Check permission bits only to allow userspace poison TCE for debug */ > if (tce_value & (TCE_PCI_WRITE | TCE_PCI_READ)) > return H_PARAMETER; > -- Alexey