linux-kernel - Re: [PATCH 09/34] x86, pkeys: store protection in high VMA flags

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Message-ID: <alpine.DEB.2.11.1512081516470.3595@nanos>
Date:	Tue, 8 Dec 2015 15:17:11 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Dave Hansen <dave@...1.net>
cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org, x86@...nel.org,
	dave.hansen@...ux.intel.com
Subject: Re: [PATCH 09/34] x86, pkeys: store protection in high VMA flags

On Thu, 3 Dec 2015, Dave Hansen wrote:
> vma->vm_flags is an 'unsigned long', so has space for 32 flags
> on 32-bit architectures.  The high 32 bits are unused on 64-bit
> platforms.  We've steered away from using the unused high VMA
> bits for things because we would have difficulty supporting it
> on 32-bit.
> 
> Protection Keys are not available in 32-bit mode, so there is
> no concern about supporting this feature in 32-bit mode or on
> 32-bit CPUs.
> 
> This patch carves out 4 bits from the high half of
> vma->vm_flags and allows architectures to set config option
> to make them available.
> 
> Sparse complains about these constants unless we explicitly
> call them "UL".
> 
> Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>

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