[PATCH QEMU HCI-8.1 v4 25/31] VZ: vfio/cpr: don't close KVM on cpr-exec

[Andrey Drobyshev <andrey.drobyshev@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>
---
 hw/vfio/cpr.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/hw/vfio/cpr.c b/hw/vfio/cpr.c
index db462aabcbf..7ca761d5bf5 100644
--- a/hw/vfio/cpr.c
+++ b/hw/vfio/cpr.c
@@ -192,13 +192,16 @@ static int vfio_cpr_kvm_close_notifier(NotifierWithReturn *notifier,
     return 0;
 }
 
+/*
+ * Not for cpr-exec: the exec closes the KVM fds anyway, and until then
+ * cpr_exec_cb() may still give up and resume the VM, which needs KVM.
+ */
 void vfio_cpr_add_kvm_notifier(void)
 {
     if (!kvm_close_notifier.notify) {
-        migration_add_notifier_modes(&kvm_close_notifier,
-                                     vfio_cpr_kvm_close_notifier,
-                                     MIG_MODE_CPR_TRANSFER, MIG_MODE_CPR_EXEC,
-                                     -1);
+        migration_add_notifier_mode(&kvm_close_notifier,
+                                    vfio_cpr_kvm_close_notifier,
+                                    MIG_MODE_CPR_TRANSFER);
     }
 }
 

-- 
2.47.1