Messages in this thread | | | Subject | Re: Crash in MM code in v4.4.y, v4.9.y with TRANSPARENT_HUGEPAGE enabled | From | Guenter Roeck <> | Date | Fri, 17 Aug 2018 17:44:08 -0700 |
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On 08/17/2018 05:25 PM, Linus Torvalds wrote: > 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? > Yes.
> 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") > I applied that patch, but it didn't help. I get exactly the same crash and traceback.
> 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. > Personally I suspect that something went wrong or is missing in the backport from 4.14 to 4.9. 5-level paging was introduced in between, and thp support was extended to support additional architectures. With all those changes, it is easy to miss something. Only I have no idea what that might be.
Guenter
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