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

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Message-ID: <20241108153411.GF38786@noisy.programming.kicks-ass.net>
Date: Fri, 8 Nov 2024 16:34:11 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Colton Lewis <coltonlewis@...gle.com>
Cc: kvm@...r.kernel.org, Oliver Upton <oliver.upton@...ux.dev>,
	Sean Christopherson <seanjc@...gle.com>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Jiri Olsa <jolsa@...nel.org>, Ian Rogers <irogers@...gle.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Kan Liang <kan.liang@...ux.intel.com>,
	Will Deacon <will@...nel.org>, Russell King <linux@...linux.org.uk>,
	Catalin Marinas <catalin.marinas@....com>,
	Michael Ellerman <mpe@...erman.id.au>,
	Nicholas Piggin <npiggin@...il.com>,
	Christophe Leroy <christophe.leroy@...roup.eu>,
	Naveen N Rao <naveen@...nel.org>,
	Heiko Carstens <hca@...ux.ibm.com>,
	Vasily Gorbik <gor@...ux.ibm.com>,
	Alexander Gordeev <agordeev@...ux.ibm.com>,
	Christian Borntraeger <borntraeger@...ux.ibm.com>,
	Sven Schnelle <svens@...ux.ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
	"H . Peter Anvin" <hpa@...or.com>, linux-perf-users@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org
Subject: Re: [PATCH v7 4/5] x86: perf: Refactor misc flag assignments

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@...gle.com>
> Reviewed-by: Oliver Upton <oliver.upton@...ux.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;