Hello, On Thu, Apr 13, 2023 at 01:49:43PM +0900, Akihiko Odaki wrote: > Hi, > > Recently I encountered a problem with the combination of Linux's > virtio-iommu driver and QEMU when a SR-IOV virtual function gets disabled. > I'd like to ask you what kind of solution is appropriate here and implement > the solution if possible. > > A PCIe device implementing the SR-IOV specification exports a virtual > function, and the guest can enable or disable it at runtime by writing to a > configuration register. This effectively looks like a PCI device is > hotplugged for the guest. Just so I understand this better: the guest gets a whole PCIe device PF that implements SR-IOV, and so the guest can dynamically create VFs? Out of curiosity, is that a hardware device assigned to the guest with VFIO, or a device emulated by QEMU? > In such a case, the kernel assumes the endpoint is > detached from the virtio-iommu domain, but QEMU actually does not detach it. > > This inconsistent view of the removed device sometimes prevents the VM from > correctly performing the following procedure, for example: > 1. Enable a VF. > 2. Disable the VF. > 3. Open a vfio container. > 4. Open the group which the PF belongs to. > 5. Add the group to the vfio container. > 6. Map some memory region. > 7. Close the group. > 8. Close the vfio container. > 9. Repeat 3-8 > > When the VF gets disabled, the kernel assumes the endpoint is detached from > the IOMMU domain, but QEMU actually doesn't detach it. Later, the domain > will be reused in step 3-8. > > In step 7, the PF will be detached, and the kernel thinks there is no > endpoint attached and the mapping the domain holds is cleared, but the VF > endpoint is still attached and the mapping is kept intact. > > In step 9, the same domain will be reused again, and the kernel requests to > create a new mapping, but it will conflict with the existing mapping and > result in -EINVAL. > > This problem can be fixed by either of: > - requesting the detachment of the endpoint from the guest when the PCI > device is unplugged (the VF is disabled) Yes, I think this is an issue in the virtio-iommu driver, which should be sending a DETACH request when the VF is disabled, likely from viommu_release_device(). I'll work on a fix unless you would like to do it > - detecting that the PCI device is gone and automatically detach it on > QEMU-side. > > It is not completely clear for me which solution is more appropriate as the > virtio-iommu specification is written in a way independent of the endpoint > mechanism and does not say what should be done when a PCI device is > unplugged. Yes, I'm not sure it's in scope for the specification, it's more about software guidance Thanks, Jean _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
