linux-kernel - Re: [PATCH 2/3] x86/apic: Add TSC

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Message-ID: <20170531215855.GA5382@khazad-dum.debian.net>
Date:   Wed, 31 May 2017 18:58:55 -0300
From:   Henrique de Moraes Holschuh <hmh@....eng.br>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     tglx@...utronix.de, x86@...nel.org, linux-kernel@...r.kernel.org,
        kevin.b.stanton@...el.com
Subject: Re: [PATCH 2/3] x86/apic: Add TSC_DEADLINE quirk due to errata

On Wed, 31 May 2017, Peter Zijlstra wrote:
> +	DEADLINE_MODEL_MATCH_REV ( INTEL_FAM6_SKYLAKE_X,	0x02000014),
...
> +	DEADLINE_MODEL_MATCH_REV ( INTEL_FAM6_SKYLAKE_MOBILE,	0xb2),
> +	DEADLINE_MODEL_MATCH_REV ( INTEL_FAM6_SKYLAKE_DESKTOP,	0xb2),
...
> +	DEADLINE_MODEL_MATCH_REV ( INTEL_FAM6_KABYLAKE_MOBILE,	0x52),
> +	DEADLINE_MODEL_MATCH_REV ( INTEL_FAM6_KABYLAKE_DESKTOP,	0x52),

Maybe these revisions need to be decreased by one, so that the SGX
behavior of messing with the microcode revision is taken into account?

When the processor microcode is auto-updated from the (signed) FIT, and
SGX's PRMRR feature is supported, the processor will report its
microcode revision as one less.  Therefore, a microcode update with
revision 0xb2 auto-loaded from FIT would be reported by RDMSR(0x8b) as
revision 0xb1.

I know about this SGX-related behavior from a coreboot commit from ~two
years ago (link below).  As far as I can tell, the Intel 64/IA32 SDM is
*still* missing any mention about this behavior in vol 3A section 9.11
(where it describes microcode updates).

https://review.coreboot.org/cgit/coreboot.git/commit/?id=5042aad4ded1651638ae9b60e34114b65e4f211e

-- 
  Henrique Holschuh