linux-kernel - Re: [PATCH] KVM: X86: Allow userspace to define the microcode version

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Date:   Mon, 26 Feb 2018 20:37:11 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Wanpeng Li <kernellwp@...il.com>,
        LKML <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>,
        Radim Krčmář <rkrcmar@...hat.com>
Subject: Re: [PATCH] KVM: X86: Allow userspace to define the microcode version

On Mon, Feb 26, 2018 at 09:39:12AM -0500, Konrad Rzeszutek Wilk wrote:
> diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
> index d19e903214b4..87d044ce837f 100644
> --- a/arch/x86/kernel/cpu/intel.c
> +++ b/arch/x86/kernel/cpu/intel.c
> @@ -144,6 +144,13 @@ static bool bad_spectre_microcode(struct cpuinfo_x86 *c)
>  {
>  	int i;
>  
> +	/*
> +	 * We know that the hypervisor lie to us on the microcode version so
> +	 * we may as well trust that it is running the correct version.
> +	 */
> +	if (boot_cpu_has(X86_FEATURE_HYPERVISOR))

I guess

	cpu_has(c, X86_FEATURE_HYPERVISOR)

since we're passing a ptr to the current CPU.

It boils down to the same thing in the end but this is bit nicer and
besides the rest of the code uses cpu_has() too.

Otherwise, yap, this looks like a good idea.

Thx.

-- 
Regards/Gruss,
    Boris.

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