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

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Date:   Wed, 28 Dec 2016 14:26:24 -0500
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Borislav Petkov <bp@...en8.de>,
        Junichi Nomura <j-nomura@...jp.nec.com>
Cc:     "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Andy Lutomirski <luto@...capital.net>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "hpa@...or.com" <hpa@...or.com>
Subject: Re: [PATCH 3/2] x86/microcode/intel: Add a helper which gives the
 microcode revision



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@...e.de>
>>
>> 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