linux-kernel - Re: [PATCH 3/5] x86-64, docs, mm: Add vsyscall range to virtual address space layout

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Date:	Mon, 4 Mar 2013 22:56:39 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	X86 ML <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/5] x86-64, docs, mm: Add vsyscall range to virtual
 address space layout

On Mon, Mar 04, 2013 at 01:45:20PM -0800, Andy Lutomirski wrote:
> vsyscalls are only 4k.  Am I missing something obvious her?

Right, but we're reserving 5 level2 pages for this, i.e. 5*512*4K = 10M.
I.e., each level2 page contains 512 ptes, each pointing to a 4K page.

arch/x86/kernel/head_64.S:

...
NEXT_PAGE(level2_fixmap_pgt)
	.fill	506,8,0
	.quad	level1_fixmap_pgt - __START_KERNEL_map + _PAGE_TABLE
	/* 8MB reserved for vsyscalls + a 2MB hole = 4 + 1 entries */
	.fill	5,8,0

NEXT_PAGE(level1_fixmap_pgt)
	.fill	512,8,0

-- 
Regards/Gruss,
    Boris.

Sent from a fat crate under my desk. Formatting is fine.
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