linux-kernel - Re: [PATCH 1/3] perf tool: precise mode requires exclude

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Date:	Mon, 10 Sep 2012 19:23:36 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	David Ahern <dsahern@...il.com>
Cc:	acme@...stprotocols.net, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...nel.org>,
	Robert Richter <robert.richter@....com>,
	Gleb Natapov <gleb@...hat.com>, Avi Kivity <avi@...hat.com>
Subject: Re: [PATCH 1/3] perf tool: precise mode requires exclude_guest

On Mon, 2012-09-10 at 10:40 -0600, David Ahern wrote:
> PEBS cannot be used with guest mode. See:
>    https://lkml.org/lkml/2012/7/9/264

Expanding and not relying on external stuff is so much better.

So in particular you want something like:

"Intel PEBS in VT-x context uses the DS address as a guest linear
address, even though its programmed by the host as a host linear
address. This either results in guest memory corruption and or the
hardware faulting and 'crashing' the virtual machine

Therefore we have to disable PEBS on VT-x enter and re-enable on VT-x
exit, enforcing a strict exclude_guest.

AMB IBS does work but doesn't currently support exclude_* at all,
setting an exclude_* bit will make it fail.

 ... explain how one can use IBS if we auto-fallback to !precise ..."

Hmm ?

> If user adds :p modifier set exclude_guest as well.
> 
> Signed-off-by: David Ahern <dsahern@...il.com>
> Cc: Ingo Molnar <mingo@...nel.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Robert Richter <robert.richter@....com>
> Cc: Gleb Natapov <gleb@...hat.com>
> Cc: Avi Kivity <avi@...hat.com>
> ---
>  tools/perf/util/parse-events.c |    3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/tools/perf/util/parse-events.c b/tools/perf/util/parse-events.c
> index a031ee1..f2c02b2 100644
> --- a/tools/perf/util/parse-events.c
> +++ b/tools/perf/util/parse-events.c
> @@ -694,6 +694,9 @@ static int get_event_modifier(struct event_modifier *mod, char *str,
>  			eH = 0;
>  		} else if (*str == 'p') {
>  			precise++;
> +			/* use of precise requires exclude_guest */
> +			if (!exclude_GH)
> +				eG = 1;
>  		} else
>  			break;
>  

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