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

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

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@...el.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)
--