linux-kernel - Re: [RFC] use realmode code to reserve end-of-conventional-memory to 1MB

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Message-Id: <1204630906.16613.4.camel@muff>
Date:	Tue, 04 Mar 2008 11:41:46 +0000
From:	Mark McLoughlin <markmc@...hat.com>
To:	Ian Campbell <ijc@...lion.org.uk>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Alexander van Heukelum <heukelum@...lshack.com>,
	Ingo Molnar <mingo@...e.hu>,
	Alexander van Heukelum <heukelum@...tmail.fm>,
	Andi Kleen <ak@...e.de>, Thomas Gleixner <tglx@...utronix.de>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] use realmode code to reserve end-of-conventional-memory
	to 1MB

On Thu, 2008-02-28 at 23:16 +0000, Ian Campbell wrote:
> On Thu, 2008-02-28 at 13:14 -0800, H. Peter Anvin wrote:
> >
> > You need to set up your memory map more sensibly; it's not just the 
> > kernel, user space tries to access these areas too.
> 
> Agreed, I think it's pure luck that Xen kernels have gotten away with it
> in the past.
> 
> The patch below seems like the right thing to do. It certainly boots in
> a domU without the DMI problem (without any of the other related patches
> such as Alexander's).

Yep, this patch on its own fixes 2.6.25-rc3 DomU boot for me here.

> x86/xen: Construct e820 map with a hole between 640K-1M.
> 
> Signed-off-by: Ian Campbell <ijc@...lion.org.uk>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: H. Peter Anvin <hpa@...or.com>
> Cc: Jeremy Fitzhardinge <jeremy@...p.org>
> ---
>  arch/x86/xen/setup.c |    3 ++-
>  1 files changed, 2 insertions(+), 1 deletions(-)
> 
> diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
> index 3bad477..2341492 100644
> --- a/arch/x86/xen/setup.c
> +++ b/arch/x86/xen/setup.c
> @@ -38,7 +38,8 @@ char * __init xen_memory_setup(void)
>  	unsigned long max_pfn = xen_start_info->nr_pages;
>  
>  	e820.nr_map = 0;
> -	add_memory_region(0, PFN_PHYS(max_pfn), E820_RAM);
> +	add_memory_region(0, LOWMEMSIZE(), E820_RAM);
> +	add_memory_region(HIGH_MEMORY, PFN_PHYS(max_pfn)-HIGH_MEMORY, E820_RAM);

Seems to me to be the right thing to do ...

Acked-by: Mark McLoughlin <markmc@...hat.com>

Cheers,
Mark.

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