> A device takes a reference to its group's kvm at the first open and
> drops it at the last close, so that device->kvm stays valid for the
> driver in between. QEMU's cpr-exec and cpr-transfer keep the device
> open while the VM is re-created, so the first VM stays referenced for
> as long as the device is: its vcpus, mm and in-kernel PIT thread with
> it. Seen as a second KVM instance in debugfs after a live update of a
> vGPU VM.
>
> Only three drivers read device->kvm after open_device(): KVMGT,
> vfio_ap and vfio-pci's zdev support. Let them say so with
> needs_kvm_ref, and take no reference for the others, which then can't
> keep a VM alive. Tested with nvidia-vgpu-vfio 595.71.03 on RTX 6000
> Ada SR-IOV VFs, a vfio-pci variant driver that doesn't read the
> pointer.
>
> Fixes: 2b48f52f2bff ("vfio: fix deadlock between group lock and kvm lock")
> https://virtuozzo.atlassian.net/browse/VSTOR-150597
> Feature: fix ms/vfio
>
> Assisted-by: LLM
> Signed-off-by: Andrey Drobyshev <[email protected]>
Sashiko has reviewed this patch and found no issues. It looks great!
--
Sashiko AI review ยท
https://sashiko.vzint.dev/#/patchset/[email protected]?part=1
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