Re: [PATCH] qemu-kvm: x86: Fix mismerge in cpu_post_load

[Gleb Natapov <gleb@redhat.com>]

On Sun, Dec 06, 2009 at 11:44:40AM +0100, Jan Kiszka wrote:
> Gleb Natapov wrote:
> > On Thu, Dec 03, 2009 at 07:21:01PM +0100, Jan Kiszka wrote:
> >> Merge 8e2c5ec2f6 forgot to restore some qemu-kvm-specific hooks in
> >> cpu_post_load. mp_state was readded later on, but tsc was missing,
> >> breaking the guest timing after resume. Also, reset of halt was dropped
> >> which is obviously required for in-kernel irqchip.
> >>
> >> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
> >> ---
> >>
> >> This solves "Problem 1" on my list.
> >>
> >> BTW, this patch just made me realize that the TSC MSR belongs to the
> >> list states that should not be written back unconditionally. Upstream
> >> does this currently, qemu-kvm not (at the price one more kvm-specific
> >> hook into generic code). Unlike the other states we discussed, this one
> >> is not "fixable" in the kernel. So I tend to think there is a real need
> >> for my write-back scope abstraction - which would also be able to handle
> >> the other states cleanly, both in upstream and here.
> >>
> >>  target-i386/machine.c |   10 +++++++++-
> >>  1 files changed, 9 insertions(+), 1 deletions(-)
> >>
> >> diff --git a/target-i386/machine.c b/target-i386/machine.c
> >> index 6bd447f..9ac477b 100644
> >> --- a/target-i386/machine.c
> >> +++ b/target-i386/machine.c
> >> @@ -366,7 +366,15 @@ static int cpu_post_load(void *opaque, int version_id)
> >>          hw_breakpoint_insert(env, i);
> >>  
> >>      tlb_flush(env, 1);
> >> -    kvm_load_mpstate(env);
> >> +
> >> +    if (kvm_enabled()) {
> >> +        /* when in-kernel irqchip is used, env->halted causes deadlock
> >> +           because no userspace IRQs will ever clear this flag */
> >> +        env->halted = 0;
> >> +
> > That is strange. env->halted should be used only for "info cpus" output
> > in case of in-kernel irqchip. Can you see where it hangs?
> 
> This line was not directly involved in the regression I saw, it was just
> the next one (load_tsc). But I simply restored qemu-kvm to the state
> before the vmstate conversion merge, dropping only obviously unneeded
> bits (namely the full register write-back).
> 
> The above line may no longer be required, but I wanted to play safe. If
> you can explain which qemu-kvm change made this obsolete, please file a
> removal patch!
> 
Ah, OK then. There was no particular patch that made in kernel irqchip
to not use env->halted. AFAIR it was always this way.

> > 
> >> +        kvm_load_tsc(env);
> >> +        kvm_load_mpstate(env);
> >> +    }
> >>  
> >>      return 0;
> >>  }
> > 
> > --
> > 			Gleb.
> 
> Jan
> 



--
			Gleb.