linux-kernel - Re: [PATCH 06/34] perf, kvm: Support the intx/intx_cp modifiers in KVM arch perfmon emulation v2

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Message-ID: <1350995765.13456.15.camel@twins>
Date:	Tue, 23 Oct 2012 14:36:05 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	x86@...nel.org, linux-kernel@...r.kernel.org, acme@...hat.com,
	eranian@...gle.com, Andi Kleen <ak@...ux.intel.com>,
	avi@...hat.com, Gleb Natapov <gleb@...hat.com>
Subject: Re: [PATCH 06/34] perf, kvm: Support the intx/intx_cp modifiers in
 KVM arch perfmon emulation v2

On Thu, 2012-10-18 at 16:19 -0700, Andi Kleen wrote:
> From: Andi Kleen <ak@...ux.intel.com>
> 
> This is not arch perfmon, but older CPUs will just ignore it. This makes
> it possible to do at least some TSX measurements from a KVM guest

Please, always CC people who wrote the code as well, in this case that's
Gleb.

> Cc: avi@...hat.com
> v2: Various fixes to address review feedback
> Signed-off-by: Andi Kleen <ak@...ux.intel.com>
> ---
>  arch/x86/kvm/pmu.c |   15 +++++++++++----
>  1 files changed, 11 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c
> index cfc258a..81c1632 100644
> --- a/arch/x86/kvm/pmu.c
> +++ b/arch/x86/kvm/pmu.c

> @@ -173,6 +173,11 @@ static void reprogram_counter(struct kvm_pmc *pmc, u32 type,
>  		.exclude_kernel = exclude_kernel,
>  		.config = config,
>  	};
> +	/* Will be ignored on CPUs that don't support this. */
> +	if (intx)
> +		attr.config |= HSW_INTX;
> +	if (intx_cp)
> +		attr.config |= HSW_INTX_CHECKPOINTED;
>  
>  	attr.sample_period = (-pmc->counter) & pmc_bitmask(pmc);
>  

So I forgot how all this worked, but will the KVM emulation not pass
this straight down to the hardware?

Don't we have a problem where we're emulating arch perfmon v1 on AMD
hardware? On AMD hardware those bits do have meaning.

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