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?) 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 -- 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/
