linux-kernel - Re: [PATCH]Fix broken VMI in 2.6.27-rc..

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Message-ID: <489B8163.3070300@kernel.org>
Date:	Thu, 07 Aug 2008 16:12:35 -0700
From:	"H. Peter Anvin" <hpa@...nel.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	Zachary Amsden <zach@...are.com>,
	Alok Kataria <akataria@...are.com>,
	Ingo Molnar <mingo@...e.hu>,
	the arch/x86 maintainers <x86@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH]Fix broken VMI in 2.6.27-rc..

Linus Torvalds wrote:
> 
> On Thu, 7 Aug 2008, H. Peter Anvin wrote:
>> Just moving it down by 4 MB doesn't help, since the VMI guys want as much as
>> 64 MB, which is half the standard vmalloc area and hence too much address
>> space lost.  We can't put it at the bottom of the vmalloc area, since that
>> boundary is not fixed, either.
> 
> Yeah, ok. Since this is a 32-bit only issue, 64MB is actually a fair chunk 
> of our already limited virtual space.
> 
>> The one remaining fixed boundary in the machine is the kernel-userspace
>> boundary.  Hence moving the 1:1 area up by one PDE unit and sticking the
>> fixmap area in that region.
> 
> Yeah, ok, but I'd be more nervous about the validation issues there. There 
> might be a lot of code that assumes that TASK_SIZE is the start of the 1:1 
> area. It does sound like a good approach, it just makes me worry about the 
> test coverage.
> 

Indeed.  Unfortunately I don't see any other options.

	-hpa
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