>-----Original Message----- >From: Eric Auger <eric.au...@redhat.com> >Subject: Re: [PATCH] hw/virtio/vhost: Disable IOTLB callbacks when IOMMU gets >disabled > >Hi Zhenzhong, > > >On 1/21/25 10:18 AM, Duan, Zhenzhong wrote: >> Hi Eric, >> >>> -----Original Message----- >>> From: Eric Auger <eric.au...@redhat.com> >>> Subject: [PATCH] hw/virtio/vhost: Disable IOTLB callbacks when IOMMU gets >>> disabled >>> >>> 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 >> Do you see this print once during one time reboot? >Actually this happens rarely on reboot. The reproducibility is of the >order of magnitude of 1/10 for me. I use a vm with vhost net device + >virtual intel iommu featuring a crontab job. >@reboot /usr/sbin/reboot >> >>> 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. >> Try to understand the sequence, is it like below? >> >> vhost vcpu >> >> call into vtd_iommu_translate(); >No that's a kernel vhost translate request that normally tries to find >out the translated address on kernel side in the IOTLB but since the >data is not there it ends up asking for the translation to user space ... >> >> set >> s->dmar_enabled = false; >> switch >> off iommu address space; >> disable >> vhost IOTLB callbacks; >vtd_handle_gcmd_write/vtd_handle_gcmd_te/vtd_handle_gcmd_te which >eventually calls vhost_iommu_region_del >> >> check if !s->dmar_enabled; >> return flat translation and trigger warning >vhost inflight translation reaches user space through >vhost_device_iotlb_miss()
Understood, thanks Eric! BRs. Zhenzhong
