On 04/04/2016 06:49, David Gibson wrote:
> There are currently 3 calls to qemu_system_reset() in vl.c. Two of them
> are immediately preceded by a cpu_synchronize_all_states9) and the
> remaining one should be.
>
> The one which doesn't is the very first reset called directly from main().
> Without a cpu_synchronize_all_states(), kvm_vcpu_dirty is false at this
> point from the earlier cpu_synchronize_all_post_init(). That's incorrect
> because the reset path is quite likely to update the CPU state, and that
> updated state should be pushed back to KVM, not overwritten with stale
> data pushed to KVM immediately after init.
>
> This patch moves the call to cpu_synchronize_all_states() into
> qemu_system_reset() for safety, so it is always called. AFAICT this should
> be safe for the handful of callers outside vl.c - these all appear to be in
> places where the cpu state is already synchronized so the extra call
> will be a no-op.
>
> Signed-off-by: David Gibson <da...@gibson.dropbear.id.au>
> ---
> vl.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> This fixes a real but on ppc - the incorrect state of kvm_vcpu_dirty
> means that an extra cpu_synchronize_state() in revised code for
> updating the MSR is not a no-op as expected and loads a stale MSR
> value, resulting in an incorrect MSR value on entry to the guest.
>
> Therefore, I'm hoping to apply this ASAP to 2.6.
>
> Laurent, could you please verify that this does indeed address the
> problem with an incorrect MSR on entry.
>
> diff --git a/vl.c b/vl.c
> index bd81ea9..3629336 100644
> --- a/vl.c
> +++ b/vl.c
> @@ -1745,6 +1745,8 @@ void qemu_system_reset(bool report)
>
> mc = current_machine ? MACHINE_GET_CLASS(current_machine) : NULL;
>
> + cpu_synchronize_all_states();
> +
> if (mc && mc->reset) {
> mc->reset();
> } else {
> @@ -1893,7 +1895,6 @@ static bool main_loop_should_exit(void)
> }
> if (qemu_reset_requested()) {
> pause_all_vcpus();
> - cpu_synchronize_all_states();
> qemu_system_reset(VMRESET_REPORT);
> resume_all_vcpus();
> if (!runstate_check(RUN_STATE_RUNNING) &&
> @@ -1903,7 +1904,6 @@ static bool main_loop_should_exit(void)
> }
> if (qemu_wakeup_requested()) {
> pause_all_vcpus();
> - cpu_synchronize_all_states();
> qemu_system_reset(VMRESET_SILENT);
> notifier_list_notify(&wakeup_notifiers, &wakeup_reason);
> wakeup_reason = QEMU_WAKEUP_REASON_NONE;
>
Acked-by: Paolo Bonzini <pbonz...@redhat.com>
