Re: [PATCH v3 07/18] x86/intel_rdt: Add Haswell feature discovery

From: Borislav Petkov <bp@suse.de>
To: "Luck, Tony" <tony.luck@intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	"H. Peter Anvin" <h.peter.anvin@intel.com>,
	Ingo Molnar <mingo@elte.hu>,
	Peter Zijlstra <peterz@infradead.org>,
	Stephane Eranian <eranian@google.com>,
	Dave Hansen <dave.hansen@intel.com>,
	Nilay Vaish <nilayvaish@gmail.com>, Shaohua Li <shli@fb.com>,
	David Carrillo-Cisneros <davidcc@google.com>,
	Ravi V Shankar <ravi.v.shankar@intel.com>,
	Sai Prakhya <sai.praneeth.prakhya@intel.com>,
	Vikas Shivappa <vikas.shivappa@linux.intel.com>,
	linux-kernel <linux-kernel@vger.kernel.org>, x86 <x86@kernel.org>
Subject: Re: [PATCH v3 07/18] x86/intel_rdt: Add Haswell feature discovery
Date: Tue, 11 Oct 2016 13:12:27 +0200	[thread overview]
Message-ID: <20161011111227.wpyvzdelxvod6e5h@pd.tnic> (raw)
In-Reply-To: <20161010185545.GA8429@intel.com>

On Mon, Oct 10, 2016 at 11:55:45AM -0700, Luck, Tony wrote:
> How about this (this diff on top of current series, but obviously we'll
> fold it into part 07.
> 
> 
> commit cdb05159fb91ed1f85c950c0f2c6de25f143961d
> Author: Tony Luck <tony.luck@intel.com>
> Date:   Mon Oct 10 11:48:42 2016 -0700
> 
>     Update the HSW probe code - better comments, and use IA32_L3_CBM_BASE
>     as the probe MSR instead of PQR_ASSOC at suggestion of h/w architect).
> 
> diff --git a/arch/x86/kernel/cpu/intel_rdt.c b/arch/x86/kernel/cpu/intel_rdt.c
> index 4903e21d660d..e3c397306f1a 100644
> --- a/arch/x86/kernel/cpu/intel_rdt.c
> +++ b/arch/x86/kernel/cpu/intel_rdt.c
> @@ -56,39 +56,39 @@ struct rdt_resource rdt_resources_all[] = {
>  
>  /*
>   * cache_alloc_hsw_probe() - Have to probe for Intel haswell server CPUs
> - * as it does not have CPUID enumeration support for Cache allocation.
> + * as they do not have CPUID enumeration support for Cache allocation.
> + * The check for Vendor/Family/Model is not enough to guarantee that
> + * the MSRs won't #GP fault because only the following SKUs support
> + * CAT:
> + *	Intel(R) Xeon(R)  CPU E5-2658 v3  @  2.20GHz
> + *	Intel(R) Xeon(R)  CPU E5-2648L v3  @  1.80GHz
> + *	Intel(R) Xeon(R)  CPU E5-2628L v3  @  2.00GHz
> + *	Intel(R) Xeon(R)  CPU E5-2618L v3  @  2.30GHz
> + *	Intel(R) Xeon(R)  CPU E5-2608L v3  @  2.00GHz
>   *
> - * Probes by writing to the high 32 bits(CLOSid) of the IA32_PQR_MSR and
> - * testing if the bits stick. Max CLOSids is always 4 and max cbm length
> + * Probe by trying to write the first of the L3 cach mask registers
> + * and checking that the bits stick. Max CLOSids is always 4 and max cbm length

I wonder what's worse - comparing SKU strings - we know that from the MCE
recovery experience - or poking at maybe nonexistent MSRs? :-)

I guess the latter is cleaner so let's try it.

Thanks for the writeup in the comments - this is exactly what I was
thinking about!

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
-- 