On Wed, Mar 18, 2015 at 3:38 PM, Stefan Seyfried <[email protected]> wrote: > Am 18.03.2015 um 23:29 schrieb Andy Lutomirski: >> On Wed, Mar 18, 2015 at 3:22 PM, Jiri Kosina <[email protected]> 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?) > > I have no good way of reproducing the issue (happens once per week...) > but apparently Takashi has, so I'd like to hand this task over to him. > >> 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. > > Unfortunately not, is this userspace memory? It's not in the dump I have. > This issue is the first I have seen where having a full dump would be > really helpful apart from cosmetic reasons...
Yes, it's userspace. Thanks for checking, though. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
