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([2a01:e0a:59e:9d80:527b:9dff:feef:3874]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-38c2a1c42fcsm3412254f8f.96.2025.01.24.09.47.59 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 24 Jan 2025 09:48:00 -0800 (PST) Message-ID: <0f8ed4d7-c4f7-46f8-a9e9-75d7a1e0cba4@redhat.com> Date: Fri, 24 Jan 2025 18:47:58 +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: "Duan, Zhenzhong" , Jason Wang Cc: "eric.auger.pro@gmail.com" , "qemu-devel@nongnu.org" , "mst@redhat.com" , "sgarzare@redhat.com" , "lvivier@redhat.com" , Peter Xu References: <20250120173339.865681-1-eric.auger@redhat.com> <5a55011a-af8f-483a-99fa-5cb2cdf3841f@redhat.com> <678babb6-f64a-4db5-ad60-494214a4e673@redhat.com> <25b5bb73-abd8-4008-905d-6c2e9e1330e2@redhat.com> From: Eric Auger In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.129.124; envelope-from=eric.auger@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -50 X-Spam_score: -5.1 X-Spam_bar: ----- X-Spam_report: (-5.1 / 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_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 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 Zhenzhong, On 1/24/25 3:44 AM, Duan, Zhenzhong wrote: > >> -----Original Message----- >> From: Eric Auger >> Subject: Re: [PATCH] hw/virtio/vhost: Disable IOTLB callbacks when IOMMU gets >> disabled >> >> Hi Jason, >> >> >> On 1/23/25 2:34 AM, Jason Wang wrote: >>> On Wed, Jan 22, 2025 at 3:55 PM Eric Auger wrote: >>>> 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? >>> Adding Peter for more ideas. >>> >>> I think it's better to find a way to trigger the listener here, probably: >>> >>> 1) add/delete the memory regions instead of enable/disable >> sorry I don't understand what you mean. The vhost_iommu_region_del call >> stack is provided below [1]. Write to the intel iommu GCMD TE bit >> induces a call to vhost_iommu_region_del. This happens before the >> vhost_dev_stop whose call stack is provided below [2] and originates > >from a bus reset. >> We may have inflight IOTLB miss requests happening between both. >> >> If this happens, vhost_device_iotlb_miss() fails because the IOVA is not >> translated anymore by the IOMMU and the iotlb.translated_addr returned >> by address_space_get_iotlb_entry() is not within the registered >> vhost_memory_regions looked up in vhost_memory_region_lookup(), hence >> the "Fail to lookup the translated address" message. >> >> It sounds wrong that vhost keeps on using IOVAs that are not translated >> anymore. It looks we have a reset ordering issue and this patch is just >> removing the sympton and not the cause. >> >> At the moment I don't really get what is initiating the intel iommu TE >> bit write. This is a guest action but is it initiated from a misordered >> qemu event? > During reboot, native_machine_shutdown() calls x86_platform.iommu_shutdown() > to disable iommu before reset. So Peter's patch will not address your issue. Exactly I see the initial IOMMU disable comes from this guest code path (native_machine_shutdown). Indeed this is unrelated to Peter's series. Then I see that vIOMMU is reset and then vhost_dev_stop is called (this is related to Peter's series). > > Before iommu shutdown, device_shutdown() is called to shutdown all devices. > Not clear why vhost is still active. That's the piece I was missing next. Thanks! Eric > > Thanks > Zhenzhong > >> It could also relate to >> [PATCH 0/4] intel_iommu: Reset vIOMMU after all the rest of devices >> https://lore.kernel.org/all/?q=s%3Aintel_iommu%3A+Reset+vIOMMU+after+all+ >> the+rest+of+devices