Messages in this thread | | | From | Andy Lutomirski <> | Date | Wed, 18 Mar 2015 15:29:14 -0700 | Subject | Re: PANIC: double fault, error_code: 0x0 in 4.0.0-rc3-2, kvm related? |
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On Wed, Mar 18, 2015 at 3:22 PM, Jiri Kosina <jkosina@suse.cz> wrote: > On Wed, 18 Mar 2015, Andy Lutomirski wrote: > >> sysret64 can only fail with #GP, and we're totally screwed if that >> happens, > > But what if the GPF handler pagefaults afterwards? It'd be operating on > user stack already.
Good point.
Stefan, can you try changing the first "jne opportunistic_sysret_failed" to "jmp opportunistic_sysret_failed" in entry_64.S and seeing if you can reproduce this? (Is it easy enough to reproduce that this would tell us anything?)
It's a shame that double_fault doesn't record what gs was on entry. If we did sysret -> general_protection -> page_fault -> double_fault, then we'd enter double_fault with usergs, whereas syscall -> page_fault -> double_fault would enter double_fault with kernelgs.
Hmm. We may be able to answer this more directly. Stefan, can you dump a couple hundred bytes starting at 0x00007fffa55eafb8 (i.e. your page_fault stack at the time of the failure)? That will tell us the faulting address. If that fails, try starting at 00007fffa55eb000 instead.
--Andy
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