Messages in this thread Patch in this message | | | Date | Sun, 21 Jun 2009 10:13:31 -0700 (PDT) | From | Linus Torvalds <> | Subject | Re: [git pull] drm: previous pull req + 1. |
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On Sun, 21 Jun 2009, Linus Torvalds wrote: > > Dave - no amount of userspace differences make a corrupted page table > acceptable. > > This needs to be fixed. No excuses. Kernel crashes are never an issue of > "you used the wrong user space".
So "corrupted page table" means that one of the reserved bits was set, and we get a page fault with the PF_RSVD bit on in the error code.
Looking at the debug output, it says
PGD 12148a067 PUD 12148b067 PMD 121496067 PTE ffffc90011780237
where the top-level entries look fine, but the PTE is total crap. It looks like it has filled in the page frame number with a virtual address rather than with an actual page
The PTE _should_ look like this:
- bit 63: NX - bits 62-52: zero (available to sw, but I don't think we use them) - bits 51-47: zero (reserved) - bits 46-12: page frame - bits 11-0: protection and PAT bits etc (bits 8-7 are also reserved)
and that PTE clearly does not match.
Strictly speaking, that "47-bit" physical address is purely theoretical. I think existing CPU's are limited to 40 bits or so, so there are even more reserved bits.
Anyway, here's a totally UNTESTED patch that hopefully gives a warning on where exactly we set the invalid bits. Andy, mind trying it out? You should get the warnign much earlier, and it should have a much more useful back-trace.
(But this is _untested_, so maybe I screwed up and it doesn't compile or work. The BAD_PTE_BITS mask could also be improved upon, but that mask should be "good enough" - it doesn't include _all_ the bits it could, but it certainly has enough bits set to trigger that obviously bad case).
Linus
--- arch/x86/include/asm/pgtable_64.h | 3 +++ 1 files changed, 3 insertions(+), 0 deletions(-)
diff --git a/arch/x86/include/asm/pgtable_64.h b/arch/x86/include/asm/pgtable_64.h index c57a301..b95828e 100644 --- a/arch/x86/include/asm/pgtable_64.h +++ b/arch/x86/include/asm/pgtable_64.h @@ -49,8 +49,11 @@ static inline void native_pte_clear(struct mm_struct *mm, unsigned long addr, *ptep = native_make_pte(0); } +#define BAD_PTE_BITS (_PAGE_NX - (1ul << __PHYSICAL_MASK_SHIFT)) + static inline void native_set_pte(pte_t *ptep, pte_t pte) { + WARN_ON_ONCE(pte.pte & BAD_PTE_BITS); *ptep = pte; }
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