On Wed, 17 Dec, at 08:54:56AM, Andy Lutomirski wrote: > [trying again with .org spelled correctly. also cc: bpetkov] > > On Wed, Dec 17, 2014 at 8:51 AM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote: > > I figured I should send this email before I forget about this issue: > > > > If you run perf record across any EFI mixed mode call or otherwise > > receive an NMI or MCE, the machine triple-faults. The cause is > > straightforward: there is no valid IDT when we have long mode disabled > > for the duration of the EFI call. Right, the lack of IDT is intentional since we disable interrupts while making the EFI call and so far I have side-stepped (ignored) the NMI/MCE issue. Perf is an interesting use case. I've admittedly never used it with EFI mixed mode, but yes, we should definitely get that working (if NMI/MCE handling wasn't justification enough). > > As far as I know, the only way to have continuously functional interrupt > > handling across a long mode transition is to install an interrupt vector > > table and hope that CPUs actually do something intelligent when > > receiving an interrupt with LME=1, LMA=1, and PG=0. Yuck. > > > > Could we get away with issuing 32-bit EFI calls in compat mode, i.e. > > with a 32-bit CPL0 CS but while still in long mode? I think that > > delivery of an IST interrupt (which includes both NMI and MCE) will > > correctly switch to a fully valid 64-bit state and would correctly > > switch back when we execute IRET at the end. (Am I missing some reason > > that switching bitness without a privilege level change doesn't work > > well? I haven't thought of anything, other than the lack of SS/SP controls > > on intra-ring interrupts, but that shouldn't be an issue here.) > > > > As an added benefit, this would considerably simplify the code. I can't immediately think of a reason that this wouldn't work, but I've Cc'd more x86 folks for additional insight. I will schedule some time to look into this issue in the new year. Thanks Andy. -- Matt Fleming, Intel Open Source Technology Center -- To unsubscribe from this list: send the line "unsubscribe linux-efi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
