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
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