linux-kernel - Re: [PATCH 0/4] memblock related fixes for -tip

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Message-ID: <4CB63E57.2000300@zytor.com>
Date:	Wed, 13 Oct 2010 16:18:47 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
CC:	Yinghai Lu <yinghai@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Vivek Goyal <vgoyal@...hat.com>
Subject: Re: [PATCH 0/4] memblock related fixes for -tip

On 10/13/2010 04:14 PM, Jeremy Fitzhardinge wrote:
> 
> The Xen code is setting the max_pfn_mapped correctly, but it is just
> being overridden by:
> 
> 	max_pfn_mapped = KERNEL_IMAGE_SIZE >> PAGE_SHIFT;
> 
> in setup_arch() - and KERNEL_IMAGE_SIZE is hard-coded to 512MB...
> 
> How is this correct?  Does kernel/head_64.S map everything up to 512MB
> or something?
> 

Yes:
        /*
         * 512 MB kernel mapping. We spend a full page on this pagetable
         * anyway.
         *
         * The kernel code+data+bss must not be bigger than that.
         *
         * (NOTE: at +512MB starts the module area, see MODULES_VADDR.
         *  If you want to increase this then increase MODULES_VADDR
         *  too.)
         */
        PMDS(0, __PAGE_KERNEL_LARGE_EXEC,
                KERNEL_IMAGE_SIZE/PMD_SIZE)

This is, however, wrong in the sense that it obviously shouldn't be
getting executed on the Xen codepath.

	-hpa
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