>-----Original Message----- >From: Eric Auger <eric.au...@redhat.com> >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 <eric.au...@redhat.com> wrote: >>> Hi Jason, >>> >>> >>> On 1/22/25 8:17 AM, Jason Wang wrote: >>>> On Wed, Jan 22, 2025 at 12:25 AM Eric Auger <eric.au...@redhat.com> >wrote: >>>>> Hi Jason, >>>>> >>>>> On 1/21/25 4:27 AM, Jason Wang wrote: >>>>>> On Tue, Jan 21, 2025 at 1:33 AM Eric Auger <eric.au...@redhat.com> >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 <eric.au...@redhat.com> >>>>>>> --- >>>>>>> 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. Before iommu shutdown, device_shutdown() is called to shutdown all devices. Not clear why vhost is still active. 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