Re: [PATCH 3/2] x86/microcode/intel: Add a helper which gives the microcode revision

[Boris Ostrovsky]

On 12/28/2016 07:53 AM, Borislav Petkov wrote:
> On Wed, Dec 28, 2016 at 12:21:20PM +0100, Borislav Petkov wrote:
> > From: Borislav Petkov <bp@xxxxxxx>
> >
> > Intel supplies the microcode revision value in MSR 0x8b
> > (IA32_BIOS_SIGN_ID) after CPUID(1) has been executed. Execute it each
> > time before reading that MSR.
>
> And then, we can go a step further and even do a separate helper which does the
> required steps to read out the microcode revision so that we don't forget them
> next time we change the code.
>
> Provided that works for xen, though, because I need to do the native
> variants but early_init_intel() can call the paravirt *msr() versions
> and I have no idea whether that's kosher on xen pv.
>
> Boris, any objections?

I think this should work. MSR_IA32_UCODE_REV can be natively read and 
written with zero without any side effects.

-boris