On 2016-03-01 23:41, Borislav Petkov wrote: > On Tue, Mar 01, 2016 at 10:11:57PM +0100, Paolo Bonzini wrote: >> I just use QEMU's binary translation mode to debug this kind of code (-d >> in_asm is useful and relatively compact (because it only shows loops >> once), > > Ha, I had forgotten about "in_asm"! Thanks for reminding me, that's a > really cool feature I'm going to use. With it I see: > > ---------------- > IN: > 0x0000000001000000: mov 0xffffffff81cba1f8,%rsp > 0x0000000001000008: callq 0x10001a9 > > ---------------- > > Now, it is obvious that 0xffffffff81cba1f8 is not mapped yet and we're > running from physical addresses. The DF tracepoint shows, in addition, > the previous exception vector causing the DF and I think that's useful. > As an additional debugging aid. Oh, and that doesn't need ept=0 and runs > at full speed. > >> or alternatively ept=0. But perhaps... why not. :) It's not like it >> adds overhead. > > Yeah, it is off by default and doesn't hurt anyone. And the diff size > is ok, IMHO. Lemme code the Intel side too and see how the whole thing > turns out. To make this a serious debug feature, we should consider trapping all exceptions on request (and reinjecting the unhandled ones). Not sure right now, though, if that comes with more complications than the simple #DF case. Jan -- Siemens AG, Corporate Technology, CT RDA ITP SES-DE Corporate Competence Center Embedded Linux -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
