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

[Peter Zijlstra]

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 <coltonle...@google.com>
> Reviewed-by: Oliver Upton <oliver.up...@linux.dev>
> ---
>  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

> +
> +     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;
}

>  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;