Re: [PATCH] trace "exit to userspace" event

[Gleb Natapov <gleb@redhat.com>]

On Thu, Oct 07, 2010 at 09:49:17PM -0300, Marcelo Tosatti wrote:
> On Thu, Oct 07, 2010 at 07:56:55PM +0200, Gleb Natapov wrote:
> > > > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> > > > index b8499f5..8800713 100644
> > > > --- a/virt/kvm/kvm_main.c
> > > > +++ b/virt/kvm/kvm_main.c
> > > > @@ -1458,6 +1458,8 @@ static long kvm_vcpu_ioctl(struct file *filp,
> > > >  		if (arg)
> > > >  			goto out;
> > > >  		r = kvm_arch_vcpu_ioctl_run(vcpu, vcpu->run);
> > > > +		if (r >= 0)
> > > > +			trace_kvm_userspace_exit(vcpu->run->exit_reason);
> > > >  		break;
> > > >  	case KVM_GET_REGS: {
> > > >  		struct kvm_regs *kvm_regs;
> > > > --
> > > > 			Gleb.
> > > 
> > > Exit codes are also valid for r == -EINTR and -EAGAIN cases, eg
> > > EXIT_INTR. Better print it out for all cases, and let the reader
> > > decide whether exit_reason is valid.
> > Are they? I see that userspace does not look into run->exit_reason in
> > case of -EINTR and -EAGAIN.
> 
> Not userspace, but for a human reader. Otherwise the trace information
> is incomplete and confusing.
But if we will always call trace_kvm_userspace_exit() here trace
information will show erroneous info since on any error but -EINTR
exit_reason contains stale info. What about changing r >= 0 to r >= 0 ||
r ==  -EINTR.

--
			Gleb.