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Re: [Qemu-ppc] [PATCH] vl: Move cpu_synchronize_all_states() into qemu_s
From: |
David Gibson |
Subject: |
Re: [Qemu-ppc] [PATCH] vl: Move cpu_synchronize_all_states() into qemu_system_reset() |
Date: |
Mon, 4 Apr 2016 17:54:35 +1000 |
User-agent: |
Mutt/1.5.24 (2015-08-30) |
On Mon, Apr 04, 2016 at 09:31:16AM +0200, Paolo Bonzini wrote:
>
>
> 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 <address@hidden>
> > ---
> > 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 <address@hidden>
Thanks Paolo.
Paolo / Peter, should I send this in a pull request for my tree, or
should it go through someone else's tree?
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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