Messages in this thread | | | From | Linus Torvalds <> | Date | Fri, 17 Aug 2018 17:25:07 -0700 | Subject | Re: Crash in MM code in v4.4.y, v4.9.y with TRANSPARENT_HUGEPAGE enabled |
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On Fri, Aug 17, 2018 at 3:27 PM Guenter Roeck <linux@roeck-us.net> wrote: > > [ 6.649970] random: crng init done > [ 6.689002] BUG: unable to handle kernel paging request at ffffeafffa1a0020
Hmm. Lots of bits set.
> [ 6.689082] RIP: 0010:[<ffffffff8116ba10>] [<ffffffff8116ba10>] page_remove_rmap+0x10/0x230 > [ 6.689082] RSP: 0018:ffffc900007abc18 EFLAGS: 00000296 > [ 6.689082] RAX: ffffea0005e58000 RBX: ffffeafffa1a0000 RCX: 0000000020200000 > [ 6.689082] RDX: 00003fffffe00000 RSI: 0000000000000001 RDI: ffffeafffa1a0000
Is that RDX value the same value as PHYSICAL_PMD_PAGE_MASK?
If I did my math right, it would be, if your CPU has 46 bits of physical memory. Might that be the case?
The reason I mention that is because we had the bug with spurious inversion of the zero pte/pmd, fixed by
f19f5c49bbc3 ("x86/speculation/l1tf: Exempt zeroed PTEs from inversion")
and that would make a zeroed pmd entry be inverted by PHYSICAL_PMD_PAGE_MASK, and then you get odd garbage page pointers etc.
Maybe. I could have gotten the math wrong too, but it sounds like the register contents _potentially_ might match up with something like this, and then we'd zap a bogus hugepage because of some confusion.
Although then I'd have expected the bisection to hit "x86/speculation/l1tf: Invert all not present mappings" instead of the one you hit, so I don't know.
Plus I'd have expected the problem to have been in mainline too, and apparently it's just the 4.4 and 4.9 backports.
Your test-case does have mprotect with PROT_NONE. Which together with that mask that *might* be PHYSICAL_PMD_PAGE_MASK makes me think it might be related.
Linus
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