linux-kernel - Re: [RFC][PATCH 1/4] x86, mpx: introduce per-mm MPX table size tracking

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Date:   Fri, 27 Jan 2017 09:26:30 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Dave Hansen <dave.hansen@...ux.intel.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org, x86@...nel.org
Subject: Re: [RFC][PATCH 1/4] x86, mpx: introduce per-mm MPX table size
 tracking


* Dave Hansen <dave.hansen@...ux.intel.com> wrote:

> Larger address spaces mean larger MPX bounds table sizes.  This
> tracks which size tables we are using.
> 
> "MAWA" is what the hardware documentation calls this feature:
> MPX Address-Width Adjust.  We will carry that nomenclature throughout
> this series.
> 
> The new field will be optimized and get packed into 'bd_addr' in a later
> patch.  But, leave it separate for now to make the series simpler.
> 
> ---
> 
>  b/arch/x86/include/asm/mmu.h |    1 +
>  b/arch/x86/include/asm/mpx.h |    9 +++++++++
>  2 files changed, 10 insertions(+)
> 
> diff -puN arch/x86/include/asm/mmu.h~mawa-020-mmu_context-mawa arch/x86/include/asm/mmu.h
> --- a/arch/x86/include/asm/mmu.h~mawa-020-mmu_context-mawa	2017-01-26 14:31:32.643673297 -0800
> +++ b/arch/x86/include/asm/mmu.h	2017-01-26 14:31:32.647673476 -0800
> @@ -34,6 +34,7 @@ typedef struct {
>  #ifdef CONFIG_X86_INTEL_MPX
>  	/* address of the bounds directory */
>  	void __user *bd_addr;
> +	int mpx_mawa;

-ENOCOMMENT.

Plus 'int' looks probably wrong, unless the hardware really wants signed shift 
values. (whatever 'mpx_mawa' is.)

Plus, while Intel is free to use sucky acronyms such as MAWA, could we please name 
this and related functionality sensibly: mpx_table_size or mpx_table_shift or 
such? The data structure comment can point out that Intel calls this 'MAWA'.

(Also, the changelog refers to a later change, which never happens in this 
series.)

Thanks,

	Ingo