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

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Date:   Sun, 9 Oct 2016 13:41:16 +0200
From:   Borislav Petkov <bp@...e.de>
To:     Fenghua Yu <fenghua.yu@...el.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <h.peter.anvin@...el.com>,
        Ingo Molnar <mingo@...e.hu>, Tony Luck <tony.luck@...el.com>,
        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 Fri, Oct 07, 2016 at 07:45:52PM -0700, Fenghua Yu wrote:
> From: Fenghua Yu <fenghua.yu@...el.com>
> 
> Some Haswell generation CPUs support RDT, but they don't enumerate this
> using CPUID.  Use rdmsr_safe() and wrmsr_safe() to probe the MSRs on
> cpu model 63 (INTEL_FAM6_HASWELL_X)
> 
> Signed-off-by: Fenghua Yu <fenghua.yu@...el.com>
> Signed-off-by: Tony Luck <tony.luck@...el.com>
> ---
>  arch/x86/events/intel/cqm.c             |  2 +-
>  arch/x86/include/asm/intel_rdt_common.h |  6 ++++++
>  arch/x86/kernel/cpu/intel_rdt.c         | 38 +++++++++++++++++++++++++++++++++
>  3 files changed, 45 insertions(+), 1 deletion(-)
>  create mode 100644 arch/x86/include/asm/intel_rdt_common.h

...

> +static inline bool cache_alloc_hsw_probe(void)
> +{
> +	u32 l, h_old, h_new, h_tmp;
> +
> +	if (rdmsr_safe(MSR_IA32_PQR_ASSOC, &l, &h_old))
> +		return false;
> +
> +	/*
> +	 * Default value is always 0 if feature is present.
> +	 */
> +	h_tmp = h_old ^ 0x1U;
> +	if (wrmsr_safe(MSR_IA32_PQR_ASSOC, l, h_tmp))

I don't understand - you do the family/model check below and yet still
use the _safe() variants. Isn't the presence of that MSR guaranteed on
those machines?

> +		return false;
> +	rdmsr(MSR_IA32_PQR_ASSOC, l, h_new);
> +
> +	if (h_tmp != h_new)
> +		return false;
> +
> +	wrmsr(MSR_IA32_PQR_ASSOC, l, h_old);
> +
> +	return true;
> +}
>  
>  static inline bool get_rdt_resources(struct cpuinfo_x86 *c)
>  {
>  	bool ret = false;
>  
> +	if (c->x86_vendor == X86_VENDOR_INTEL && c->x86 == 6 &&
> +	    c->x86_model == INTEL_FAM6_HASWELL_X)
> +		return cache_alloc_hsw_probe();
> +
>  	if (!cpu_has(c, X86_FEATURE_RDT_A))
>  		return false;
>  	if (cpu_has(c, X86_FEATURE_CAT_L3))
> -- 
> 2.5.0
> 

-- 
Regards/Gruss,
    Boris.

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