linux-kernel - Re: [PATCH 1/5] perf: Add hardware breakpoint address mask

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Date:	Sun, 21 Apr 2013 18:43:33 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Jacob Shin <jacob.shin@....com>
Cc:	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org,
	Stephane Eranian <eranian@...gle.com>,
	Jiri Olsa <jolsa@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/5] perf: Add hardware breakpoint address mask

On 04/20, Jacob Shin wrote:
>
> On Sat, Apr 20, 2013 at 06:22:23PM +0200, Oleg Nesterov wrote:
> > On 04/09, Jacob Shin wrote:
> > >
> > > @@ -612,6 +612,9 @@ static int hw_breakpoint_add(struct perf_event *bp, int flags)
> > >  	if (!(flags & PERF_EF_START))
> > >  		bp->hw.state = PERF_HES_STOPPED;
> > >
> > > +	if (bp->attr.bp_addr_mask && !arch_has_hw_breakpoint_addr_mask())
> > > +		return -EOPNOTSUPP;
> > > +
> >
> > This is called by sched_in... Isn't it "too late" ?
> >
> > Perhaps arch_validate_hwbkpt_settings() should validate mask/cpu_has_bpext?
>
> Ah, yes okay. Should I do this for all the archs that HAVE_HW_BREAKPOINT ?
>
> Or is creating HAVE_HW_BREAKPOINT_ADDR_MASK and in validate_hw_breakpoint:
>
>   #ifndef HAVE_HW_BREAKPOINT_ADDR_MASK
>   if (bp->attr.bp_addr_mask)
>   	return -EOPNOTSUPP;
>   #endif

Or a __weak function overridden in amd.c. I do not know what would be
better, up to you.

Hmm. But this patch already defines arch_has_hw_breakpoint_addr_mask()
for any arch, so validate_hw_breakpoint() can just use it?

Oleg.

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