Subject: Re: [PATCH v6 4/5] x86: perf: Refactor misc flag assignments

From: "Liang, Kan" <[email-masked]>
Date: Wed, 6 Nov 2024 11:03:10 -0500

On 2024-11-05 2:56 p.m., 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 <[email-masked]>
> Reviewed-by: Oliver Upton <[email-masked]>
> ---
>  arch/x86/events/core.c            | 31 +++++++++++++++++++++++--------
>  arch/x86/include/asm/perf_event.h |  2 ++
>  2 files changed, 25 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
> index d19e939f3998..24910c625e3d 100644
> --- a/arch/x86/events/core.c
> +++ b/arch/x86/events/core.c
> @@ -3011,16 +3011,34 @@ 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);
> +
> +	if (guest_state & PERF_GUEST_USER)
> +		flags |= PERF_RECORD_MISC_GUEST_USER;
> +	else if (guest_state & PERF_GUEST_ACTIVE)
> +		flags |= PERF_RECORD_MISC_GUEST_KERNEL;
> +

The logic of setting the GUEST_KERNEL flag is implicitly changed here.

For the current code, the GUEST_KERNEL flag is set for !PERF_GUEST_USER,
which include both guest_in_kernel and guest_in_NMI.

With the above change, the GUEST_KERNEL flag should be only set for the
guest_in_kernel case.
IIUC, this is the series's target, right?

If so, could you please move the explanation into this patch?
For x86, the behavior has already been changed since this patch.

Thanks,
Kan

> +	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);
>  
>  	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);
>  	} else {
>  		if (user_mode(regs))
>  			misc |= PERF_RECORD_MISC_USER;
> @@ -3028,9 +3046,6 @@ unsigned long perf_arch_misc_flags(struct pt_regs *regs)
>  			misc |= PERF_RECORD_MISC_KERNEL;
>  	}
>  
> -	if (regs->flags & PERF_EFLAGS_EXACT)
> -		misc |= PERF_RECORD_MISC_EXACT_IP;
> -
>  	return misc;
>  }
>  
> diff --git a/arch/x86/include/asm/perf_event.h b/arch/x86/include/asm/perf_event.h
> index feb87bf3d2e9..d95f902acc52 100644
> --- a/arch/x86/include/asm/perf_event.h
> +++ b/arch/x86/include/asm/perf_event.h
> @@ -538,7 +538,9 @@ struct x86_perf_regs {
>  
>  extern unsigned long perf_arch_instruction_pointer(struct pt_regs *regs);
>  extern unsigned long perf_arch_misc_flags(struct pt_regs *regs);
> +extern unsigned long perf_arch_guest_misc_flags(struct pt_regs *regs);
>  #define perf_arch_misc_flags(regs)	perf_arch_misc_flags(regs)
> +#define perf_arch_guest_misc_flags(regs)	perf_arch_guest_misc_flags(regs)
>  
>  #include <asm/stacktrace.h>
>