William Lee Irwin III <[email protected]> writes:
> On Tue, May 01, 2007 at 05:58:29AM +0200, Andi Kleen wrote:
>> From: [email protected]
>> 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 <[email protected]>
>> ---
>> 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 <[email protected]>
> 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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