Messages in this thread | | | Date | Tue, 20 May 2008 05:14:14 +0100 (BST) | From | Hugh Dickins <> | Subject | Re: [Bug 10732] REGRESSION: 2.6.26-rc2-git4: X server failed start onX61s laptop |
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On Mon, 19 May 2008, Linus Torvalds wrote: > On Mon, 19 May 2008, Hugh Dickins wrote: > > > > This comes from an assumption in 1c12c4cf9411eb130b245fa8d0fbbaf989477c7b > > mprotect: prevent alteration of the PAT bits, that PTE_MASK is what it's > > supposed to be: whereas it's been wrong forever with PAE, staying 32-bit > > where 64-bit is needed. > > Can we *please* just fix PTE_MASK?
That's very much what I'd prefer too. Jeremy has patches in Ingo's tree to do that, which have been tested - though perhaps not in combination with the PAT pte_modify changes. I did check that they're not incompatible in theory, but I sure better try them out later today.
> And can we agree to never EVER use that PAGE_MASK thing (which was only > ever meant to work on *addresses*) for any pte operations (including the > definition of PTE_MASK)? Because PAGE_MASK is very much the word-size, and > in 32-bit PAE, the page table entry is bigger. > > IOE, PTE_MASK should be a "pteval_t". And it should have absolutely > *nothing* to do with PAGE_MASK. EVER.
Yes, Jeremy makes it a pteval_t. (My builds and Ingo's builds succeed, but I've not worked out how that goes down in assembly: there was an _AT macro in there before, which you've kept too - Jeremy?)
> IOW, maybe something like this? > > And no, I haven't tested this at all. But it should make PTE_MASK have > (a) the right type ("pteval_t", not "long" - the latter is pure and utter > crap) > (b) the right value (proper mask, not a sign-extended long - again, the > latter is pure and utter crap) > > but for all I know there might be some broken code that depends on the > current incorrect and totally broken #defines, so this needs testing and > thinking about.
Yes, I'm highly resistant to taking untested patches here. The two-liner I sent last night was about my fifth attempt to get it working, and I did start off from a small PTE_MASK correction which didn't work at all. It looked rather like yours, I guess I missed the __PHYSICAL_LOW_BITS part. Jeremy's goes a lot further, he'll know the gotchas better.
> It also causes these warnings on 32-bit PAE: > > AS arch/x86/kernel/head_32.o > arch/x86/kernel/head_32.S: Assembler messages: > arch/x86/kernel/head_32.S:225: Warning: left operand is a bignum; integer 0 assumed > arch/x86/kernel/head_32.S:609: Warning: left operand is a bignum; integer 0 assumed > > and I do not see why (the end result seems to be identical). > > Ingo, comments? > > Oh, and those #define's should be moved from <asm/page.h> to > <asm/pgtable.h>, I think. They have nothing to do with pages (despite the > name of "physical_page_mask", and really are meaningful only in the > context of some kind of page table entry.
Jeremy still has them in asm/page.h. Like your subsequent pte bit cleanups, that can be added later: the important thing is to get X working again on 32-bit NX systems.
Hugh
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