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([2a01:e0a:59e:9d80:527b:9dff:feef:3874]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-46e102ec283sm61431671cf.2.2025.01.21.23.55.26 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 21 Jan 2025 23:55:28 -0800 (PST) Message-ID: <678babb6-f64a-4db5-ad60-494214a4e673@redhat.com> Date: Wed, 22 Jan 2025 08:55:24 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] hw/virtio/vhost: Disable IOTLB callbacks when IOMMU gets disabled Content-Language: en-US To: Jason Wang Cc: eric.auger.pro@gmail.com, qemu-devel@nongnu.org, mst@redhat.com, sgarzare@redhat.com, lvivier@redhat.com, zhenzhong.duan@intel.com References: <20250120173339.865681-1-eric.auger@redhat.com> <5a55011a-af8f-483a-99fa-5cb2cdf3841f@redhat.com> From: Eric Auger In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=eric.auger@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -51 X-Spam_score: -5.2 X-Spam_bar: ----- X-Spam_report: (-5.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-2.996, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.086, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: eric.auger@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Hi Jason, On 1/22/25 8:17 AM, Jason Wang wrote: > On Wed, Jan 22, 2025 at 12:25 AM Eric Auger wrote: >> >> Hi Jason, >> >> On 1/21/25 4:27 AM, Jason Wang wrote: >>> On Tue, Jan 21, 2025 at 1:33 AM Eric Auger wrote: >>>> When a guest exposed with a vhost device and protected by an >>>> intel IOMMU gets rebooted, we sometimes observe a spurious warning: >>>> >>>> Fail to lookup the translated address ffffe000 >>>> >>>> We observe that the IOMMU gets disabled through a write to the global >>>> command register (CMAR_GCMD.TE) before the vhost device gets stopped. >>>> When this warning happens it can be observed an inflight IOTLB >>>> miss occurs after the IOMMU disable and before the vhost stop. In >>>> that case a flat translation occurs and the check in >>>> vhost_memory_region_lookup() fails. >>>> >>>> Let's disable the IOTLB callbacks when all IOMMU MRs have been >>>> unregistered. >>>> >>>> Signed-off-by: Eric Auger >>>> --- >>>> hw/virtio/vhost.c | 4 ++++ >>>> 1 file changed, 4 insertions(+) >>>> >>>> diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c >>>> index 6aa72fd434..128c2ab094 100644 >>>> --- a/hw/virtio/vhost.c >>>> +++ b/hw/virtio/vhost.c >>>> @@ -931,6 +931,10 @@ static void vhost_iommu_region_del(MemoryListener *listener, >>>> break; >>>> } >>>> } >>>> + if (QLIST_EMPTY(&dev->iommu_list) && >>>> + dev->vhost_ops->vhost_set_iotlb_callback) { >>>> + dev->vhost_ops->vhost_set_iotlb_callback(dev, false); >>>> + } >>> So the current code assumes: >>> >>> 1) IOMMU is enabled before vhost starts >>> 2) IOMMU is disabled after vhost stops >>> >>> This patch seems to fix 2) but not 1). Do we need to deal with the >>> IOMMU enabled after vhost starts? >> sorry I initially misunderstood the above comment. Indeed in the reboot >> case assumption 2) happens to be wrong. However what I currently do is: >> stop listening to iotlb miss requests from the kernel because my >> understanding is those requests are just spurious ones, generate >> warnings and we do not care since we are rebooting the system. >> >> However I do not claim this could handle the case where the IOMMU MR >> would be turned off and then turned on. I think in that case we should >> also flush the kernel IOTLB and this is not taken care of in this patch. >> Is it a relevant use case? > Not sure. > >> wrt removing assumption 1) and allow IOMMU enabled after vhost start. Is >> that a valid use case as the virtio driver is using the dma api? > It should not be but we can't assume the behaviour of the guest. It > could be buggy or even malicious. agreed > > Btw, we had the following codes while handling te: > > /* Handle Translation Enable/Disable */ > static void vtd_handle_gcmd_te(IntelIOMMUState *s, bool en) > { > if (s->dmar_enabled == en) { > return; > } > > trace_vtd_dmar_enable(en); > > ... > > vtd_reset_caches(s); > vtd_address_space_refresh_all(s); > } > > vtd_address_space_refresh_all() will basically disable the iommu > memory region. It looks not sufficient to trigger the region_del > callback, maybe we should delete the region or introduce listener > callback? This is exactly the code path which is entered in my use case. vtd_address_space_refresh_all(s) induces the vhost_iommu_region_del. But given the current implement of this latter the IOTLB callback is not unset and the kernel IOTLB is not refreshed. Also as I pointed out the hdev->mem->regions are not updated? shouldn't they. Can you explain what they correspond to? Thanks Eric > > Thanks > >> Eric >> >> >>> Thanks >>> >>>> } >>>> >>>> void vhost_toggle_device_iotlb(VirtIODevice *vdev) >>>> -- >>>> 2.47.1 >>>>