linux-kernel - Re: [PATCH v9 2/5] x86/cpuid: Add generic table for cpuid dependencies

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Date:   Sun, 8 Oct 2017 10:35:35 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Andi Kleen <andi@...stfloor.org>
cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Andi Kleen <ak@...ux.intel.com>,
        Jonathan McDowell <noodles@...th.li>
Subject: Re: [PATCH v9 2/5] x86/cpuid: Add generic table for cpuid
 dependencies

On Fri, 6 Oct 2017, Andi Kleen wrote:

> From: Andi Kleen <ak@...ux.intel.com>
> 
> Some CPUID features depend on other features. Currently it's
> possible to to clear dependent features, but not clear the base features,
> which can cause various interesting problems.
> 
> This patch implements a generic table to describe dependencies
> between CPUID features, to be used by all code that clears
> CPUID.
> 
> Some subsystems (like XSAVE) had an own implementation of this,
> but it's better to do it all in a single place for everyone.
> 
> Then clear_cpu_cap and setup_clear_cpu_cap always look up
> this table and clear all dependencies too.
> 
> This is intended to be a practical table: only for features
> that make sense to clear. If someone for example clears FPU,
> or other features that are essentially part of the required
> base feature set, not much is going to work. Handling
> that is right now out of scope. We're only handling
> features which can be usefully cleared.
> 
> v2: Add EXPORT_SYMBOL for clear_cpu_cap for lguest
> v3:
> Fix handling of depending issues
> Fix dups in the table (Jonathan McDowell)
> v4:
> Remove EXPORT_SYMBOL again as lguest is gone
> Restructure dependencies as feature, dependency (Thomas Gleixner)
> Move some code from header file to C file and turn macros into inlines (dito)
> Simplify if conditions (dito)
> Add missing dependency for AVX512F->AVX
> v5:
> Remove redundant dependency for AVX512F->XSAVE (Thomas Gleixner)
> Add missing dependency for XMM->FXSR (Thomas Gleixner)
> v6:
> Add SHA_NI->XMM and FXSR_OPT->FXSAVE dependencies
> Cc: Jonathan McDowell <noodles@...th.li>
> Signed-off-by: Andi Kleen <ak@...ux.intel.com>

Reviewed-by: Thomas Gleixner <tglx@...utronix.de>