Re: [PATCH RFC] KVM: inject #UD if instruction emulation fails while vcpu is in cpl==3

[Gleb Natapov <gleb@redhat.com>]

On Thu, May 06, 2010 at 12:15:58PM +0300, Avi Kivity wrote:
> On 04/29/2010 02:58 PM, Gleb Natapov wrote:
> >Do not kill VM If instruction emulation fails while vcpu is in
> >userspace. Inject #UD instead in a hope that guest OS will kill offending
> >process. Emulation failure is still traced by ftrace point to help
> >analyze the problem.
> 
> Still there's the risk here that a critical failure goes unnoticed.
> ftrace isn't on at all times.
> 
Kvm_stat will still show that there was emulation failure, so if strange
application behaviour is reported kvm_stat output will have hints where
to look. Next step in analyzing the problem will be enabling emulator
tracing.

> We can probably inject a #UD unconditionally and exit to userspace.
> Userspace would then report the problem to the user and reenter the
> guest, which would then recover or not.
> 
By "unconditionally" you mean even if guest is in kernel mode? There is
no point in trying to continue after that happens. Instead of getting
paused VM at exact place where problem happened and easily analyzable we
will get misbehaved VM with undefined state.

--
			Gleb.