Re: [PATCH v7 4/5] x86: perf: Refactor misc flag assignments

[Colton Lewis]

Peter Zijlstra <peterz@xxxxxxxxxxxxx> writes:

> On Thu, Nov 07, 2024 at 07:03:35PM +0000, Colton Lewis wrote:
> > Break the assignment logic for misc flags into their own respective
> > functions to reduce the complexity of the nested logic.

> > Signed-off-by: Colton Lewis <coltonlewis@xxxxxxxxxx>
> > Reviewed-by: Oliver Upton <oliver.upton@xxxxxxxxx>
> > ---
> >   arch/x86/events/core.c            | 32 +++++++++++++++++++++++--------
> >   arch/x86/include/asm/perf_event.h |  2 ++
> >   2 files changed, 26 insertions(+), 8 deletions(-)

> > diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
> > index d19e939f3998..9fdc5fa22c66 100644
> > --- a/arch/x86/events/core.c
> > +++ b/arch/x86/events/core.c
> > @@ -3011,16 +3011,35 @@ unsigned long  
> > perf_arch_instruction_pointer(struct pt_regs *regs)
> >   	return regs->ip + code_segment_base(regs);
> >   }

> > +static unsigned long common_misc_flags(struct pt_regs *regs)
> > +{
> > +	if (regs->flags & PERF_EFLAGS_EXACT)
> > +		return PERF_RECORD_MISC_EXACT_IP;
> > +
> > +	return 0;
> > +}
> > +
> > +unsigned long perf_arch_guest_misc_flags(struct pt_regs *regs)
> > +{
> > +	unsigned long guest_state = perf_guest_state();
> > +	unsigned long flags = common_misc_flags(regs);

> This is double common_misc and makes no sense

I'm confused what you mean. Are you referring to starting with
common_misc_flags in both perf_arch_misc_flags and
perf_arch_guest_misc_flags so possibly the common_msic_flags are set
twice?

That seems like a good thing that common flags are set wherever they
apply. You can't guarantee where perf_arch_guest_misc_flags may be
called in the future.
> > +
> > +	if (!(guest_state & PERF_GUEST_ACTIVE))
> > +		return flags;
> > +
> > +	if (guest_state & PERF_GUEST_USER)
> > +		return flags & PERF_RECORD_MISC_GUEST_USER;
> > +	else
> > +		return flags & PERF_RECORD_MISC_GUEST_KERNEL;

> And this is just broken garbage, right?

> > +}

> Did you mean to write:

> unsigned long perf_arch_guest_misc_flags(struct pt_regs *regs)
> {
> 	unsigned long guest_state = perf_guest_state();
> 	unsigned long flags = 0;

> 	if (guest_state & PERF_GUEST_ACTIVE) {
> 		if (guest_state & PERF_GUEST_USER)
> 			flags |= PERF_RECORD_MISC_GUEST_USER;
> 		else
> 			flags |= PERF_RECORD_MISC_GUEST_KERNEL;
> 	}

> 	return flags;
> }

Ok, my mistake was using & instead of |, but the branches are
functionally the same.

I'll use something closer to your suggestion.

> >   unsigned long perf_arch_misc_flags(struct pt_regs *regs)
> >   {
> >   	unsigned int guest_state = perf_guest_state();
> > -	int misc = 0;
> > +	unsigned long misc = common_misc_flags(regs);

> Because here you do the common thing..


> >   	if (guest_state) {
> > -		if (guest_state & PERF_GUEST_USER)
> > -			misc |= PERF_RECORD_MISC_GUEST_USER;
> > -		else
> > -			misc |= PERF_RECORD_MISC_GUEST_KERNEL;
> > +		misc |= perf_arch_guest_misc_flags(regs);

> And here you mix in the guest things.

> >   	} else {
> >   		if (user_mode(regs))
> >   			misc |= PERF_RECORD_MISC_USER;