linux-kernel - Re: [PATCH V2 2/3] perf protect LBR when Intel PT is enabled.

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Date:	Mon, 7 Jul 2014 17:46:35 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Liang, Kan" <kan.liang@...el.com>
Cc:	Andi Kleen <andi@...stfloor.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>
Subject: Re: [PATCH V2 2/3] perf protect LBR when Intel PT is enabled.

On Mon, Jul 07, 2014 at 01:57:16PM +0000, Liang, Kan wrote:
> > > This doesn't work, e.g. hardware debuggers can take over at any time.
> > 
> > Tough cookies. Hardware debuggers get to deal with whatever crap they
> > cause.
> 
> If so, I think I may discard this patch (2/3). I will resubmit the
> other two patches as a patch set to only handle the KVM issue we
> found.  It checks the access of LBR and extra MSRs at the
> initialization time and set the flags. So we just need to check the
> flags at runtime and avoid the protection by _safe(). 

Right.

> For Intel PT and LBR handling, since the PT codes haven't been
> integrated yet, I will try to implement another patch later.  The
> patch will add flags for LBR and PT.  When enabling PT, it checks LBR
> flag and update the PT flag. When enabling LBR, it checks PT flag and
> update the LBR flag. When disabling LBR/PT, we just update the related
> flags. we don't need to add _safe or extra rmsr in fast path. 

Yeah, should be part of the PT patches.

> How do you think?

With my brain, much like all primates :-)

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