linux-kernel - Re: [PATCH 04/12] powerpc: Implement hw_breakpoint_arch

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Date:   Fri, 25 May 2018 16:05:57 +0200
From:   Frederic Weisbecker <frederic@...nel.org>
To:     Michael Ellerman <mpe@...erman.id.au>
Cc:     LKML <linux-kernel@...r.kernel.org>, Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Joel Fernandes <joel.opensrc@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Chris Zankel <chris@...kel.net>,
        Paul Mackerras <paulus@...ba.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Will Deacon <will.deacon@....com>,
        Rich Felker <dalias@...c.org>, Ingo Molnar <mingo@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Max Filippov <jcmvbkbc@...il.com>
Subject: Re: [PATCH 04/12] powerpc: Implement hw_breakpoint_arch_parse()

On Thu, May 24, 2018 at 12:01:52PM +1000, Michael Ellerman wrote:
> Frederic Weisbecker <frederic@...nel.org> writes:
> 
> > diff --git a/arch/powerpc/kernel/hw_breakpoint.c b/arch/powerpc/kernel/hw_breakpoint.c
> > index 348cac9..fba6527 100644
> > --- a/arch/powerpc/kernel/hw_breakpoint.c
> > +++ b/arch/powerpc/kernel/hw_breakpoint.c
> > @@ -139,30 +139,31 @@ int arch_bp_generic_fields(int type, int *gen_bp_type)
> >  /*
> >   * Validate the arch-specific HW Breakpoint register settings
> >   */
> > -int arch_validate_hwbkpt_settings(struct perf_event *bp)
> > +int hw_breakpoint_arch_parse(struct perf_event *bp,
> > +			     struct perf_event_attr *attr,
> > +			     struct arch_hw_breakpoint *hw)
> 
> I think the semantics here are that we are reading from bp/attr and
> writing to hw?
> 
> If so would some sprinkling of const on the first two parameters help
> make that clearer?

I seem to remember there was an issue with that due to the various functions
we call that need to be converted to take const as well. I thought I would
do it in a seperate series but actually it should be no big deal to do it
on this one.

Let me try that and respin.

> >  	/*
> >  	 * Since breakpoint length can be a maximum of HW_BREAKPOINT_LEN(8)
> > @@ -176,12 +177,12 @@ int arch_validate_hwbkpt_settings(struct perf_event *bp)
> >  	if (cpu_has_feature(CPU_FTR_DAWR)) {
> >  		length_max = 512 ; /* 64 doublewords */
> >  		/* DAWR region can't cross 512 boundary */
> > -		if ((bp->attr.bp_addr >> 10) != 
> > -		    ((bp->attr.bp_addr + bp->attr.bp_len - 1) >> 10))
> > +		if ((attr->bp_addr >> 10) !=
> > +		    ((attr->bp_addr + attr->bp_len - 1) >> 10))
> >  			return -EINVAL;
> 
> This will conflict with my next branch, but it should be easy enough to
> resolve.

Ok.

> 
> >  	}
> > -	if (info->len >
> > -	    (length_max - (info->address & HW_BREAKPOINT_ALIGN)))
> > +	if (hw->len >
> > +	    (length_max - (hw->address & HW_BREAKPOINT_ALIGN)))
> >  		return -EINVAL;
> >  	return 0;
> >  }
> 
> Acked-by: Michael Ellerman <mpe@...erman.id.au>

Thanks!