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Date: Wed, 17 Jun 2020 15:52:59 -0700
From: Nadav Amit <nadav.amit@...il.com>
To: John Andersen <john.s.andersen@...el.com>
Cc: corbet@....net,
 Paolo Bonzini <pbonzini@...hat.com>,
 Thomas Gleixner <tglx@...utronix.de>,
 mingo <mingo@...hat.com>,
 bp <bp@...en8.de>,
 hpa@...or.com,
 shuah@...nel.org,
 sean.j.christopherson@...el.com,
 rick.p.edgecombe@...el.com,
 kvm@...r.kernel.org,
 kernel-hardening@...ts.openwall.com
Subject: Re: [kvm-unit-tests PATCH] x86: Add control register pinning tests

> On Jun 17, 2020, at 3:46 PM, John Andersen <john.s.andersen@...el.com> wrote:
> 
> Paravirutalized control register pinning adds MSRs guests can use to
> discover which bits in CR0/4 they may pin, and MSRs for activating
> pinning for any of those bits.
> 

[ sni[

> +static void vmx_cr_pin_test_guest(void)
> +{
> +	unsigned long i, cr0, cr4;
> +
> +	/* Step 1. Skip feature detection to skip handling VMX_CPUID */
> +	/* nop */

I do not quite get this comment. Why do you skip checking whether the
feature is enabled? What happens if KVM/bare-metal/other-hypervisor that
runs this test does not support this feature?

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