linux-kernel - Re: [PATCH V2 1/4] perf: Add hardware breakpoint address mask

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Date:	Thu, 25 Apr 2013 01:08:51 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Jacob Shin <jacob.shin@....com>
Cc:	Oleg Nesterov <oleg@...hat.com>, 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 V2 1/4] perf: Add hardware breakpoint address mask

2013/4/23 Jacob Shin <jacob.shin@....com>:
> From: Jacob Shin <jacob.shin@....com>
> Date: Mon, 22 Apr 2013 17:02:37 -0500
> Subject: [PATCH 1/4] perf: Add hardware breakpoint address mask
>
> Some architectures (for us, AMD Family 16h) allow for "don't care" bit
> mask to further qualify a hardware breakpoint address, in order to
> trap on range of addresses. Update perf uapi to add bp_addr_mask field.

It would be nice to describe a bit what this "don't care" bit mask is
about. Is it a range of address/bitmask to ignore in the middle of the
range we want to breakpoint in? I mean, that's confusing.

>
> Signed-off-by: Jacob Shin <jacob.shin@....com>
> ---
>  include/uapi/linux/perf_event.h |    5 ++++-
>  kernel/events/hw_breakpoint.c   |    9 +++++++++
>  2 files changed, 13 insertions(+), 1 deletion(-)
>
> diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
> index fb104e5..e22e1d1 100644
> --- a/include/uapi/linux/perf_event.h
> +++ b/include/uapi/linux/perf_event.h
> @@ -286,7 +286,10 @@ struct perf_event_attr {
>                 __u64           config1; /* extension of config */
>         };
>         union {
> -               __u64           bp_len;
> +               struct {
> +                       __u32           bp_len;
> +                       __u32           bp_addr_mask;
> +               };

Do we need len and mask to work at the same time? I can't think of a
situation when len and mask mix up together in a useful way to define
a range.

Thanks.
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