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    SubjectRe: [PATCH] [30/30] x86_64: Add missing !X86_PAE dependincy to the 2G/2G split.
    Date
    William Lee Irwin III <wli@holomorphy.com> writes:

    > On Tue, May 01, 2007 at 05:58:29AM +0200, Andi Kleen wrote:
    >> From: ebiederm@xmission.com
    >> When in PAE mode we require that the user kernel divide to be
    >> on a 1G boundary. The 2G/2G split does not have that property
    >> so require !X86_PAE
    >> Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
    >> ---
    >> arch/i386/Kconfig | 1 +
    >> 1 files changed, 1 insertions(+), 0 deletions(-)
    >
    > What on earth?
    >
    > config PAGE_OFFSET
    > hex
    > default 0xB0000000 if VMSPLIT_3G_OPT
    > default 0x78000000 if VMSPLIT_2G
    > default 0x40000000 if VMSPLIT_1G
    > default 0xC0000000
    >
    > This appears to have been introduced by:
    > commit 975b3d3d5b983eb60706d35f0d24cd19f6badabf
    > Author: Mark Lord <lkml@rtr.ca>
    > Date: Wed Feb 1 03:06:11 2006 -0800
    > [PATCH] VMSPLIT config options
    >
    > There's some sort of insanity going on here. Since when is 0x78000000
    > a 2GB/2GB split? Mark, dare I ask what you were thinking? That should
    > be VMSPLIT_2G_OPT for 2GB laptops analogously to VMSPLIT_3G_OPT, if
    > nothing else, as it's certainly not 2GB/2GB.

    It makes a little more sense when you realize all of the options
    were originally !X86_PAE. So they were designed with highmem
    disabled.

    > These VMSPLIT config options vs. PAE are foul as they're now done in
    > any event. If they were done properly, they'd properly set up the pmd
    > within which the division point between user and kernelspace falls.

    They were designed to avoid highmem a totally different design point.

    > This patch, I suppose, stops people from shooting themselves in the
    > foot, but (IMHO) the VMSPLIT patches shouldn't have been merged
    > without handling the partial pmd case. 2MB/4MB resolution is enough
    > granularity for any reasonable purpose, so split ptes aren't worth the
    > effort, but this nonsense with PAE vs. VMSPLIT is just preposterous.
    > If you're going to play the VMSPLIT game at all, handle split pmd's.

    What I find telling is that I fixed this based on code review not
    based on bug reports.

    > I'll see what else is pending in the i386 pagetable arena and clear
    > this up if there aren't other objections (this is where Andi gets to
    > complain that things are too complex already and preemptively NAK to
    > save me the effort, if it's not seen to be desirable). Eric, your patch
    > is a reasonable stop-gap measure for the original deficiency.

    Frankly rather then putting much effort into this I suspect we should
    just delete these options entirely. We are long past the point where
    they matter.

    Eric
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