Re: KVM PMU virtualization

["Zhang, Yanmin" <yanmin_zhang@linux.intel.com>]

On Wed, 2010-03-03 at 11:13 +0100, Peter Zijlstra wrote:
> On Wed, 2010-03-03 at 17:27 +0800, Zhang, Yanmin wrote:
> > +static inline u64 perf_instruction_pointer(struct pt_regs *regs)
> > +{
> > +       u64 ip;
> > +       ip = percpu_read(perf_virt_ip.ip);
> > +       if (!ip)
> > +               ip = instruction_pointer(regs);
> > +       else
> > +               perf_reset_virt_ip();
> > +       return ip;
> > +}
> > +
> > +static inline unsigned int perf_misc_flags(struct pt_regs *regs)
> > +{
> > +       if (percpu_read(perf_virt_ip.ip)) {
> > +               return percpu_read(perf_virt_ip.user_mode) ?
> > +                       PERF_RECORD_MISC_GUEST_USER :
> > +                       PERF_RECORD_MISC_GUEST_KERNEL;
> > +       } else
> > +               return user_mode(regs) ? PERF_RECORD_MISC_USER :
> > +                                PERF_RECORD_MISC_KERNEL;
> > +} 
> 
> This codes in the assumption that perf_misc_flags() must only be called
> before perf_instruction_pointer(), which is currently true, but you
> might want to put a comment near to remind us of this.
I will change the logic with a clear reset operation in caller.