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Date: Fri, 28 Oct 2016 00:38:54 +0200 (CEST)
From: Thomas Gleixner <tglx@linutronix.de>
To: Andy Lutomirski <luto@amacapital.net>
cc: Kyle Huey <me@kylehuey.com>,
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Subject: Re: [PATCH v7 6/6] x86/arch_prctl: Add ARCH_[GET|SET]_CPUID
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On Thu, 27 Oct 2016, Andy Lutomirski wrote:
> On Thu, Oct 27, 2016 at 4:15 AM, Thomas Gleixner <tglx@linutronix.de> wrote:
> Let's just do this right from day one:
> 
> static void set_cpuid_faulting(bool on)
> {
>   u64 msrval;
> 
>   DEBUG_LOCKS_WARN_ON(!irqs_disabled());
> 
>   msrval = this_cpu_read(msr_misc_features_enables_shadow);
>   msrval &= CPUID_FAULT_ENABLE;
>   msrval |= (on << CPUID_FAULT_ENABLE_BIT);
>   this_cpu_write(msr_misc_features_enables_shadow, msrval);
>   wrmsrl(MSR_MISC_FEATURES_ENABLES, msrval);
> }
> 
> RDMSR may be considerably faster than WRMSR, but that doesn't mean it's *fast*.

Good point!