Re: [PATCH QEMU HCI-8.1 v7 29/35] VZ: vfio/cpr: don't close KVM on cpr-exec

[no-reply@sashiko.virtuozzo.com]

> With VFIO devices, KVM is closed on the source when the migration
> completes, so that the new QEMU can create its own KVM VM with the same
> devices.  That is done from a migration notifier, which for cpr-exec
> runs before cpr_exec_cb().  But cpr_exec_cb() may still give up, when
> the memory can't be preserved or execve() fails, and resume the VM in
> the old QEMU.  A VM without KVM can't resume: kvm_close() removes the
> vCPU threads, and the first KVM ioctl of vm_start() aborts QEMU
> (KVM_SET_CLOCK in kvmclock_vm_state_change()).
> 
> cpr-exec doesn't need it anyway: the KVM fds are close-on-exec, so the
> kernel closes them during execve(), before the new QEMU runs, and
> kvm_vm_release() tears down the irqfds then.  Keep the notifier for
> cpr-transfer only, where the source process lives on.
> 
> Tested on the vfio-net rig: cpr-exec 5/5; a cpr-exec aborted in
> preserve_ram() and one with a bogus cpr-exec-command both left the VM
> running with no lost pings, and a later cpr-exec completed.
> 
> Signed-off-by: Andrey Drobyshev <andrey.drobyshev@virtuozzo.com>

Sashiko has reviewed this patch and found no issues. It looks great!

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Sashiko AI review · https://sashiko.vzint.dev/#/patchset/20261103-vfio_v1-v7-0-4467fdccbbe6@virtuozzo.com?part=29