>-----Original Message----- >From: Eric Farman <far...@linux.ibm.com> >Subject: Re: [PATCH 2/2] vfio/ccw: Don't initialize HOST_IOMMU_DEVICE >with mdev > >On Mon, 2024-07-22 at 17:36 +0200, Cédric Le Goater wrote: >> On 7/22/24 17:09, Joao Martins wrote: >> > On 22/07/2024 15:57, Eric Farman wrote: >> > > On Mon, 2024-07-22 at 15:07 +0800, Zhenzhong Duan wrote: >> > > > mdevs aren't "physical" devices and when asking for backing IOMMU >info, >> > > > it fails the entire provisioning of the guest. Fix that by setting >> > > > vbasedev->mdev true so skipping HostIOMMUDevice initialization in >the >> > > > presence of mdevs. >> > > >> > > Hmm, picking the two commits that Cedric mentioned in his cover- >letter reply [1] doesn't "fail the entire provisioning of the guest" for me. >> > > >> > > Applying this patch on top of that causes the call from >vfio_attach_device() to hiod_legacy_vfio_realize() to be skipped, which >seems odd. What am I missing? >> > > >> > > [1] https://lore.kernel.org/qemu-devel/4c9a184b-514c-4276-95ca- >9ed86623b...@redhat.com/ >> > > >> > >> > If you are using IOMMUFD >> > > >Which is not the case in defconfig. > >> > it will fail the entire provisioning i.e. GET_HW_INFO >> > fails because there's no actual device/IOMMU you can probe hardware >information >> > from and you can't start a guest. This happened at least for me in x86 >vfio-pci >> > mdevs (or at least I reproduced it when trying to test mdev_tty) >> > >> > But if you don't support IOMMUFD, then it probably makes no difference >as type1 >> > doesn't do anything particularly special besides initializing some static >data. > >This was my concern. The static data doesn't look particularly exciting, but it >does seem strange to >be skipping over it in the non-iommufd case now.
Thanks Joao and Cédric for helping explain and confirm. Yes, after this fix HostIOMMUDevice is totally bypassed for mdev even in non-iommufd case. In non-iommufd case, the only supported HostIOMMUDevice capability is aw_bits which is calculated through bcontainer->iova_ranges which is always NULL for mdev. So HOST_IOMMU_DEVICE_CAP_AW_BITS_MAX(64) is returned which is larger enough that vIOMMU can safely ignore. Then we can safely bypass entire HostIOMMUDevice for mdev. Thanks Zhenzhong > >> > The realize is skipped because you technically don't have a physical host >IOMMU >> > directly behind the mdev, but rather some parent function related >software >> > entity doing that for you. >> > >> > Zhengzhong noticed there were some other mdevs aside from vfio-pci >and in an >> > attempt to prevent regression elsewhere it posted for the other mdevs in >qemu. >> >> >> yes. I confirm with : >> >> -device vfio-ap,id=hostdev0,sysfsdev=/sys/bus/mdev/devices/8eb8351a- >e656-4187-b773-fea4e926310d,iommufd=iommufd0 \ >> -object iommufd,id=iommufd0 \ >> -trace 'iommufd*' >> >> iommufd_cdev_getfd /dev/vfio/devices/vfio4 (fd=28) > >Ah, right... Need to enable iommufd AND vfio_device_cdev to get into this >potential situation. I >guess this is better than random failures down the road. > >Acked-by: Eric Farman <far...@linux.ibm.com> > >> iommufd_backend_connect fd=27 owned=1 users=1 >> iommufd_cdev_connect_and_bind [iommufd=27] Successfully bound >device 8eb8351a-e656-4187-b773-fea4e926310d (fd=28): output devid=1 >> iommufd_backend_alloc_ioas iommufd=27 ioas=2 >> iommufd_cdev_alloc_ioas [iommufd=27] new IOMMUFD container with >ioasid=2 >> iommufd_cdev_attach_ioas_hwpt [iommufd=27] Successfully attached >device 8eb8351a-e656-4187-b773-fea4e926310d (28) to id=2 >> iommufd_backend_map_dma iommufd=27 ioas=2 iova=0x0 >size=0x200000000 addr=0x3fd9ff00000 readonly=0 (0) >> iommufd_cdev_device_info 8eb8351a-e656-4187-b773-fea4e926310d >(28) num_irqs=1 num_regions=0 flags=33 >> iommufd_cdev_detach_ioas_hwpt [iommufd=27] Successfully detached >8eb8351a-e656-4187-b773-fea4e926310d >> iommufd_backend_unmap_dma iommufd=27 ioas=2 iova=0x0 >size=0x200000000 (0) >> iommufd_backend_free_id iommufd=27 id=2 (0) >> iommufd_backend_disconnect fd=-1 users=0 >> >> qemu-kvm: -device vfio- >ap,id=hostdev0,sysfsdev=/sys/bus/mdev/devices/8eb8351a-e656-4187- >b773-fea4e926310d,iommufd=iommufd0: vfio 8eb8351a-e656-4187-b773- >fea4e926310d: Failed to get hardware info: No such file or directory >> >> >> >> Thanks, >> >> C. >> >>
