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Re: [PATCH 10/28] i386: map enough initial memory to create lowmem mappings

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From: Jeremy Fitzhardinge <jeremy@...>
To: H. Peter Anvin <hpa@...>
Cc: Eric W. Biederman <ebiederm@...>, Chuck Ebbert <cebbert@...>, Andi Kleen <ak@...>, Andrew Morton <akpm@...>, <virtualization@...>, lkml <linux-kernel@...>, Zachary Amsden <zach@...>, Chris Wright <chrisw@...>, Linus Torvalds <torvalds@...>
Subject: Re: [PATCH 10/28] i386: map enough initial memory to create lowmem mappings
Date: Monday, April 23, 2007 - 1:02 pm

H. Peter Anvin wrote:

No, we map enough space to map 4G (~4 pages), but we don't actually map
4G.  If a hole happened to start within that 4 page mapping, then the
memory still wouldn't be available for allocation.

I think this is a bit of a spurious argument though, since if it were
really a problem we'd have to worry about holes hitting the kernel image
too.  As far as I can see, that's not considered to be a problem.

I think the real point is that there's currently a subtle dependency
between head.S and bootmem allocation which happens between start_kernel
and pagetable_init.  Your patch preventing over-mapping should make them
easier to smoke out as it currently stands, but eliminating the problem
by making alloc_bootmem create the mappings for itself does have
appeal.  There would still be the dependency on head.S to map the kernel
itself and the bootmem allocator bitmap.

    J
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Messages in current thread:
[PATCH 10/28] i386: map enough initial memory to create lowm..., Jeremy Fitzhardinge, (Sat Apr 14, 4:42 pm)
Re: [PATCH 10/28] i386: map enough initial memory to create ..., Chuck Ebbert, (Thu Apr 19, 4:47 pm)
Re: [PATCH 10/28] i386: map enough initial memory to create ..., Andi Kleen, (Thu Apr 19, 4:50 pm)
Re: [PATCH 10/28] i386: map enough initial memory to create ..., H. Peter Anvin, (Thu Apr 19, 4:55 pm)
Re: [PATCH 10/28] i386: map enough initial memory to create ..., Andi Kleen, (Thu Apr 19, 5:04 pm)
Re: [PATCH 10/28] i386: map enough initial memory to create ..., H. Peter Anvin, (Thu Apr 19, 5:11 pm)
Re: [PATCH 10/28] i386: map enough initial memory to create ..., Chuck Ebbert, (Thu Apr 19, 5:22 pm)
Re: [PATCH 10/28] i386: map enough initial memory to create ..., Jeremy Fitzhardinge, (Thu Apr 19, 5:35 pm)
Re: [PATCH 10/28] i386: map enough initial memory to create ..., Eric W. Biederman, (Mon Apr 23, 5:12 am)
Re: [PATCH 10/28] i386: map enough initial memory to create ..., Jeremy Fitzhardinge, (Mon Apr 23, 12:34 pm)
Re: [PATCH 10/28] i386: map enough initial memory to create ..., H. Peter Anvin, (Mon Apr 23, 12:42 pm)
Re: [PATCH 10/28] i386: map enough initial memory to create ..., Eric W. Biederman, (Mon Apr 23, 1:21 pm)
Re: [PATCH 10/28] i386: map enough initial memory to create ..., Jeremy Fitzhardinge, (Mon Apr 23, 2:06 pm)
Re: [PATCH 10/28] i386: map enough initial memory to create ..., Eric W. Biederman, (Mon Apr 23, 2:54 pm)
Re: [PATCH 10/28] i386: map enough initial memory to create ..., Jeremy Fitzhardinge, (Mon Apr 23, 3:10 pm)
Re: [PATCH 10/28] i386: map enough initial memory to create ..., H. Peter Anvin, (Mon Apr 23, 3:14 pm)
Re: [PATCH 10/28] i386: map enough initial memory to create ..., Jeremy Fitzhardinge, (Mon Apr 23, 3:21 pm)
Re: [PATCH 10/28] i386: map enough initial memory to create ..., Eric W. Biederman, (Mon Apr 23, 3:39 pm)
Re: [PATCH 10/28] i386: map enough initial memory to create ..., H. Peter Anvin, (Mon Apr 23, 4:41 pm)
Re: [PATCH 10/28] i386: map enough initial memory to create ..., Jeremy Fitzhardinge, (Mon Apr 23, 1:02 pm)
Re: [PATCH 10/28] i386: map enough initial memory to create ..., Eric W. Biederman, (Mon Apr 23, 1:31 pm)
Re: [PATCH 10/28] i386: map enough initial memory to create ..., H. Peter Anvin, (Mon Apr 23, 1:45 pm)
Re: [PATCH 10/28] i386: map enough initial memory to create ..., Eric W. Biederman, (Mon Apr 23, 1:52 pm)
Re: [PATCH 10/28] i386: map enough initial memory to create ..., Andi Kleen, (Mon Apr 23, 1:54 pm)
Re: [PATCH 10/28] i386: map enough initial memory to create ..., H. Peter Anvin, (Mon Apr 23, 1:22 pm)
Re: [PATCH 10/28] i386: map enough initial memory to create ..., Eric W. Biederman, (Mon Apr 23, 2:00 pm)
Re: [PATCH 10/28] i386: map enough initial memory to create ..., H. Peter Anvin, (Mon Apr 23, 12:01 pm)
Re: [PATCH 10/28] i386: map enough initial memory to create ..., Eric W. Biederman, (Wed Apr 25, 4:54 pm)
Re: [PATCH 10/28] i386: map enough initial memory to create ..., Jeremy Fitzhardinge, (Wed Apr 25, 5:31 pm)
Re: [PATCH 10/28] i386: map enough initial memory to create ..., Eric W. Biederman, (Wed Apr 25, 6:00 pm)
Re: [PATCH 10/28] i386: map enough initial memory to create ..., Jeremy Fitzhardinge, (Wed Apr 25, 6:06 pm)
Re: [PATCH 10/28] i386: map enough initial memory to create ..., Eric W. Biederman, (Sun Apr 29, 12:44 pm)
Re: [PATCH 10/28] i386: map enough initial memory to create ..., Jeremy Fitzhardinge, (Sun Apr 29, 12:55 pm)
Re: [PATCH 10/28] i386: map enough initial memory to create ..., Eric W. Biederman, (Wed Apr 25, 6:18 pm)
Re: [PATCH 10/28] i386: map enough initial memory to create ..., Jeremy Fitzhardinge, (Wed Apr 25, 6:52 pm)
Re: [PATCH 10/28] i386: map enough initial memory to create ..., Eric W. Biederman, (Wed Apr 25, 7:33 pm)
Re: [PATCH 10/28] i386: map enough initial memory to create ..., Jeremy Fitzhardinge, (Wed Apr 25, 7:41 pm)
Re: [PATCH 10/28] i386: map enough initial memory to create ..., Chris Wright, (Wed Apr 25, 8:33 pm)
Re: [PATCH 10/28] i386: map enough initial memory to create ..., Jeremy Fitzhardinge, (Wed Apr 25, 8:55 pm)
Re: [PATCH 10/28] i386: map enough initial memory to create ..., H. Peter Anvin, (Sat Apr 14, 6:04 pm)
Re: [PATCH 10/28] i386: map enough initial memory to create ..., Jan Engelhardt, (Sun Apr 15, 5:46 am)
Re: [PATCH 10/28] i386: map enough initial memory to create ..., Andreas Schwab, (Sun Apr 15, 6:17 am)