Message-ID: <506F0A90.7020106@zytor.com>
Date: Fri, 05 Oct 2012 09:28:00 -0700
From: "H. Peter Anvin" <hpa@zytor.com>
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To: Jan Beulich <JBeulich@suse.com>
CC: matt@console-pimps.org, matt.fleming@intel.com, mingo@kernel.org,
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Subject: Re: [PATCH 1/3] x86, mm: Include the entire kernel memory map in
 trampoline_pgd
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On 10/04/2012 11:39 PM, Jan Beulich wrote:
>>
>> We should have the check, but at least for Linux support we require
>> P <= V-2.
>
> Not really imo - P <= V - 1 should be sufficient here, as all that is
> necessary is that the result represents a 1:1 mapping. Specifically,
> there's no constraint to the virtual space limitation of the direct
> mapping of RAM.
>

The P <= V-2 limitation doesn't come from this, it comes from the fact 
that we need to have the regular kernel 1:1 map and still have space for 
the kernel, vmalloc, ioremap and so on in the kernel part of the address 
space; in theory it *could* be some fraction between 1 and 2, but since 
hardware doesn't do fractional bits very well the above is what we have 
been telling the hardware folks. :)

	-hpa
-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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