Re: [PATCH] do not enter vcpu again if it was stopped during IO

[Gleb Natapov <gleb@redhat.com>]

On Mon, Jun 21, 2010 at 05:43:04PM -0300, Marcelo Tosatti wrote:
> On Mon, Jun 21, 2010 at 12:01:52PM +0300, Gleb Natapov wrote:
> > To prevent reentering vcpu after IO completion it is not enough
> > to set env->stopped since it is checked only in main loop but control
> > will not get there until next non-IO exit since kvm_run() will reenter
> > vcpu to complete IO instruction. Solve this by sending self-signal to
> > request exit after IO instruction completion.
> > 
> > Signed-off-by: Gleb Natapov <gleb@redhat.com>
> > diff --git a/qemu-kvm.c b/qemu-kvm.c
> > index be1dac2..4f7cf6d 100644
> > --- a/qemu-kvm.c
> > +++ b/qemu-kvm.c
> > @@ -603,6 +603,10 @@ int kvm_run(CPUState *env)
> >      r = pre_kvm_run(kvm, env);
> >      if (r)
> >          return r;
> > +    if (env->exit_request) {
> > +        env->exit_request = 0;
> > +        pthread_kill(env->kvm_cpu_state.thread, SIG_IPI);
> > +    }
> >      r = ioctl(fd, KVM_RUN, 0);
> 
> Can't you check for env->stopped instead?
> 
Why it would be better? exit_request is used exactly for purpose to
notify cpu loop that is should exit. Sometimes it may be useful to
request cpu exit without stopping the cpu. I see gdbstub uses it, haven't
check if it applicable to kvm though.

> >  
> >      if (r == -1 && errno != EINTR && errno != EAGAIN) {
> > diff --git a/vl.c b/vl.c
> > index 9e9c176..dcfab13 100644
> > --- a/vl.c
> > +++ b/vl.c
> > @@ -1817,6 +1817,7 @@ void qemu_system_reset_request(void)
> >      }
> >      if (cpu_single_env) {
> >          cpu_single_env->stopped = 1;
> > +        cpu_exit(cpu_single_env);
> >      }
> >      qemu_notify_event();
> >  }
> > --
> > 			Gleb.

--
			Gleb.