From: Eduardo Habkost <ehabk...@redhat.com>
Try to explain why commit 317b0a6d8ba44e9bf8f9c3dbd776c4536843d82c
needed a cpu_clean_all_dirty() call just after calling
cpu_synchronize_all_states().
Signed-off-by: Eduardo Habkost <ehabk...@redhat.com>
Cc: Andrey Korolyov <and...@xdel.ru>
Cc: Marcin Gibuła <m.gib...@beyond.pl>
Cc: Marcelo Tosatti <mtosa...@redhat.com>
Cc: Paolo Bonzini <pbonz...@redhat.com>
Signed-off-by: Paolo Bonzini <pbonz...@redhat.com>
(cherry picked from commit 1154d84dcc5f46e83db94281d071775819dd8884)
Signed-off-by: Michael Roth <mdr...@linux.vnet.ibm.com>
---
hw/i386/kvm/clock.c | 14 ++++++++++++++
1 file changed, 14 insertions(+)
diff --git a/hw/i386/kvm/clock.c b/hw/i386/kvm/clock.c
index 1ac60d6..58be2bd 100644
--- a/hw/i386/kvm/clock.c
+++ b/hw/i386/kvm/clock.c
@@ -127,7 +127,21 @@ static void kvmclock_vm_state_change(void *opaque, int
running,
}
cpu_synchronize_all_states();
+ /* In theory, the cpu_synchronize_all_states() call above wouldn't
+ * affect the rest of the code, as the VCPU state inside CPUState
+ * is supposed to always match the VCPU state on the kernel side.
+ *
+ * In practice, calling cpu_synchronize_state() too soon will load the
+ * kernel-side APIC state into X86CPU.apic_state too early, APIC state
+ * won't be reloaded later because CPUState.vcpu_dirty==true, and
+ * outdated APIC state may be migrated to another host.
+ *
+ * The real fix would be to make sure outdated APIC state is read
+ * from the kernel again when necessary. While this is not fixed, we
+ * need the cpu_clean_all_dirty() call below.
+ */
cpu_clean_all_dirty();
+
ret = kvm_vm_ioctl(kvm_state, KVM_GET_CLOCK, &data);
if (ret < 0) {
fprintf(stderr, "KVM_GET_CLOCK failed: %s\n", strerror(ret));
--
1.9.1
