Thank you Jun! Now I understand that there is a strong need to support this scenario where the host might run into trouble executing binaries with instructions unknown to it. I am still wondering if there is a way to actually exit KVM on UD from a syscall instruction without modifying the KVM kernel module? Best regards, Alex On Mon, May 5, 2014 at 7:07 PM, Nakajima, Jun <jun.nakajima@xxxxxxxxx> wrote: > On Mon, May 5, 2014 at 11:48 AM, Alexandru Duţu <alex.dutu@xxxxxxxxx> wrote: >> Thank you Jun! I see that in case of VMX does not emulated the >> instruction that produced a UD exception, it just queues the exception >> and returns 1. After that KVM will still try to enter virtualized >> execution and so forth, the execution probably finishing with a DF and >> shut down. It does not seem that KVM, in case of VMX, will exit >> immediately on UD. >> >> I am not sure what you meant with MOVBE emulation. > > I meant: > > commit 84cffe499b9418d6c3b4de2ad9599cc2ec50c607 > Author: Borislav Petkov <bp@xxxxxxx> > Date: Tue Oct 29 12:54:56 2013 +0100 > > kvm: Emulate MOVBE > > This basically came from the need to be able to boot 32-bit Atom SMP > guests on an AMD host, i.e. a host which doesn't support MOVBE. As a > matter of fact, qemu has since recently received MOVBE support but we > cannot share that with kvm emulation and thus we have to do this in the > host. We're waay faster in kvm anyway. :-) > > So, we piggyback on the #UD path and emulate the MOVBE functionality. > With it, an 8-core SMP guest boots in under 6 seconds. > > Also, requesting MOVBE emulation needs to happen explicitly to work, > i.e. qemu -cpu n270,+movbe... > > Just FYI, a fairly straight-forward boot of a MOVBE-enabled 3.9-rc6+ > kernel in kvm executes MOVBE ~60K times. > > Signed-off-by: Andre Przywara <andre@xxxxxxxxx> > Signed-off-by: Borislav Petkov <bp@xxxxxxx> > Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx> > > > -- > Jun > Intel Open Source Technology Center -- Alex -- 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
