linux-kernel - Re: Intel PT not work on 4.5-rc6 as well after suspend/resume assembler

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Date:	Wed, 2 Mar 2016 09:02:34 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	Andi Kleen <ak@...ux.intel.com>
Cc:	Adrian Hunter <adrian.hunter@...el.com>,
	Andi Kleen <andi@...stfloor.org>, jolsa@...nel.org,
	namhyung@...nel.org, alexander.shishkin@...el.com,
	linux-kernel@...r.kernel.org
Subject: Re: Intel PT not work on 4.5-rc6 as well after suspend/resume
 assembler

Em Tue, Mar 01, 2016 at 03:49:53PM -0800, Andi Kleen escreveu:
> On Tue, Mar 01, 2016 at 12:35:24PM -0300, Arnaldo Carvalho de Melo wrote:
> > Em Mon, Feb 29, 2016 at 04:25:49PM -0300, Arnaldo Carvalho de Melo escreveu:
> > > Em Mon, Feb 29, 2016 at 06:35:28PM +0100, Andi Kleen escreveu:
> > > > > What kernel have you used for testing this? 4.5-rc? I'm having trouble
> > > > > with intel_pt with 4.5.0-rc4 :-\

> > > > Works for me (on -rc5). What problem do you see?

> > > Doesn't work for me on (4.5.0-rc4), but after your report of it working
> > > my -rc4 .config and built -rc6+ with it, now it seems to work as
> > > expected, will test your patch with it later.

> > Humm, after suspend/resume it is back not working, using your example
> > for this case:
 
> PT is always disabled when VT-x is active.
 
> I guess the problem is here that it doesn't get reenabled when context switching 
> out of the guest. Need to add some code to KVM to do this (similar to how PEBS is handled)
 
> However it should work again when you stop the KVM guest and restart the trace.

Right, if there are no KVM guests running, Intel PT is back working,
which is rather incovenient :-\

- Arnaldo