linux-kernel - Re: [PATCH] perf/x86: Disable uncore on virtualized CPU.

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Date:	Wed, 5 Sep 2012 20:52:33 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	"Yan, Zheng" <zheng.z.yan@...el.com>, a.p.zijlstra@...llo.nl,
	eranian@...gle.com, mingo@...e.hu, andi@...stfloor.org,
	avi@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf/x86: Disable uncore on virtualized CPU.

On Wed, Sep 05, 2012 at 08:35:24AM +0200, Ingo Molnar wrote:
> 
> * Yan, Zheng <zheng.z.yan@...el.com> wrote:
> 
> > From: "Yan, Zheng" <zheng.z.yan@...el.com>
> > 
> > Initializing uncore PMU on virtualized CPU may hang the kernel.
> > This is because kvm does not emulate the entire hardware. Thers
> > are lots of uncore related MSRs, making kvm enumerate them all
> > is a non-trival task. So just disable uncore on virtualized CPU.
> > 
> > Signed-off-by: Yan, Zheng <zheng.z.yan@...el.com>
> > ---
> >  arch/x86/kernel/cpu/perf_event_intel_uncore.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/arch/x86/kernel/cpu/perf_event_intel_uncore.c b/arch/x86/kernel/cpu/perf_event_intel_uncore.c
> > index 0a55710..2f005ba 100644
> > --- a/arch/x86/kernel/cpu/perf_event_intel_uncore.c
> > +++ b/arch/x86/kernel/cpu/perf_event_intel_uncore.c
> > @@ -2898,6 +2898,9 @@ static int __init intel_uncore_init(void)
> >  	if (boot_cpu_data.x86_vendor != X86_VENDOR_INTEL)
> >  		return -ENODEV;
> >  
> > +	if (cpu_has_hypervisor)
> > +		return -ENODEV;
> > +
> >  	ret = uncore_pci_init();
> >  	if (ret)
> >  		goto fail;
> 
> Cannot the presence of the uncore hardware be detected in a 
> cleaner fashion, via the PCI config space and such?

Probably just by reading the registers and see that they are 0 and 
when writing read back and check.

And the code should not hang when that happens, then this check wouldn't
be needed.

-Andi
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