On Thu, Jul 23, 2015 at 2:46 PM, Willy Tarreau <w...@1wt.eu> wrote: > On Thu, Jul 23, 2015 at 05:31:05PM -0400, Steven Rostedt wrote: >> On Thu, 23 Jul 2015 14:08:59 -0700 >> Linus Torvalds <torva...@linux-foundation.org> wrote: >> >> > On Thu, Jul 23, 2015 at 1:49 PM, Andy Lutomirski <l...@amacapital.net> >> > wrote: >> > > >> > > Issue A: to return with RF clear, we need to disarm the breakpoint. >> > > If it's limited to the duration of the NMI, that's easy. If not, when >> > > do we re-arm? New prepare_exit_to_usermode hook? Hmm, setting ti >> > > flags during context switch may target the wrong task. >> > >> > We don't re-arm it. >> > >> >> Let me get this straight. The idea is in the #DB handler to detect that >> it was triggered in NMI context, and if so, simply disarm that >> breakpoint permanently, right? >> >> Nothing should be adding hw breakpoints to NMI code anyway. Sounds >> perfectly reasonable to me. Of course, how we tell we are in NMI >> brings back all the races as we had in the nesting code. We can check >> the per-cpu variable that is set with nmi_enter() and cleared at >> nmi_exit() but what happens if the breakpoint is outside those calls. >> We can check the stack pointer, but then we are back to userspace >> fooling us. Maybe add the DF trick again? > > Can't the back link of the TSS tell us where we come from ? At least > it should not be manipulable from user-space.
Not on 64-bit -- there are no tasks :) --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
