On Friday 04 January 2008 01:17:34 Balaji Rao wrote: > On Thursday 03 January 2008 14:05:28 Ingo Molnar wrote: > > * Rusty Russell <[EMAIL PROTECTED]> wrote: > > > On Thursday 03 January 2008 00:27:10 [EMAIL PROTECTED] wrote: > > > > (sorry for breaking the thread but i didn't get the original headers) > > > > > > > > > After 17d57a9206b4de6ad082ac9f2d2346985abbd2aa > > > > > (x86: fix x86-32 early fixmap initialization.) removing lg.ko > > > > > caused a printk from vunmap: > > > > > > > > > > mm/memory.c:115: bad pgd 004b3027. > > > > > > > > > > On the second use after module load, the kernel crashes. > > > > > > > > > > This fixes the immediate problem (accessed and dirty bits not set > > > > > as expected in pmd_none_or_clear_bad). I can't see why this would > > > > > cause a crash, but I haven't been able to reproduce it once this is > > > > > applied. > > > > > > > > it's the 'clear_bad' part that zero's out the pmd and hence destroys > > > > all the fixmap mappings in that 4 MB range leading to page faults at > > > > probably the most unexpected times. > > > > > > Thanks, I had misread the code as clearing it normally anyway. This > > > is a nasty bug because we'd hit it if we ever filled vmalloc space, > > > but now Linus has applied that patch we should all be merry... > > > > wanna send a patch for the p?d_bad() bug as well? (it should ignore any > > differences in the dirty/accessed bits) > > Hi Ingo, > I just tried this and I stop getting the 'bad pgd' error. Is it the right > way to do it ? > > Index: linux/include/asm/pgtable_32.h > =================================================================== > --- linux.orig/include/asm/pgtable_32.h 2008-01-03 19:16:29.000000000 > +0530 > +++ linux/include/asm/pgtable_32.h 2008-01-03 19:16:49.000000000 +0530 > @@ -206,7 +206,8 @@ > /* To avoid harmful races, pmd_none(x) should check only the lower when > PAE */ #define pmd_none(x) (!(unsigned long)pmd_val(x)) > #define pmd_present(x) (pmd_val(x) & _PAGE_PRESENT) > -#define pmd_bad(x) ((pmd_val(x) & (~PAGE_MASK & ~_PAGE_USER)) != > _KERNPG_TABLE) +#define pmd_bad(x) \ > + (!(pmd_val(x) & (~PAGE_MASK & ~_PAGE_USER & ~_KERNPG_TABLE)) & > (_PAGE_ACCESSED | _PAGE_DIRTY))
I don't agree with this idea: catching these errors is a nice warning, but I wonder if we should simply try to fix it up in this case rather than zeroing it. Cheers, Rusty. _______________________________________________ Lguest mailing list [email protected] https://ozlabs.org/mailman/listinfo/lguest
