Re: [PATCH v2 4/4] KVM: x86: Add VCPU substate for NMI states

[Gleb Natapov <gleb@redhat.com>]

On Mon, Oct 19, 2009 at 06:32:54PM -0200, Marcelo Tosatti wrote:
> On Thu, Oct 15, 2009 at 07:05:36PM +0200, Jan Kiszka wrote:
> > This plugs an NMI-related hole in the VCPU synchronization between
> > kernel and user space. So far, neither pending NMIs nor the inhibit NMI
> > mask was properly read/set which was able to cause problems on
> > vmsave/restore, live migration and system reset. Fix it by making use
> > of the new VCPU substate interface.
> > 
> > Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
> > ---
> > 
> >  Documentation/kvm/api.txt       |   12 ++++++++++++
> >  arch/x86/include/asm/kvm.h      |    7 +++++++
> >  arch/x86/include/asm/kvm_host.h |    2 ++
> >  arch/x86/kvm/svm.c              |   22 ++++++++++++++++++++++
> >  arch/x86/kvm/vmx.c              |   30 ++++++++++++++++++++++++++++++
> >  arch/x86/kvm/x86.c              |   26 ++++++++++++++++++++++++++
> >  6 files changed, 99 insertions(+), 0 deletions(-)
> > 
> > diff --git a/Documentation/kvm/api.txt b/Documentation/kvm/api.txt
> > index bee5bbd..e483edb 100644
> > --- a/Documentation/kvm/api.txt
> > +++ b/Documentation/kvm/api.txt
> > @@ -848,3 +848,15 @@ Deprecates: KVM_GET/SET_CPUID2
> >  Architectures: x86
> >  Payload: struct kvm_lapic
> >  Deprecates: KVM_GET/SET_LAPIC
> > +
> > +6.8 KVM_X86_VCPU_STATE_NMI
> > +
> > +Architectures: x86
> > +Payload: struct kvm_nmi_state
> > +Deprecates: -
> > +
> > +struct kvm_nmi_state {
> > +       __u8 pending;
> > +       __u8 masked;
> > +       __u8 pad1[6];
> 
> Don't you also have to save "nmi_injected", in case of failure during
> NMI delivery.
> 
> BTW, what happens to exceptions that fail to be delivered? Can't see
> where they are saved/restored across migration.
> 
The instruction that caused an exception will be re-executed after
migration and exception will be regenerated. But I think we should
migrate exception anyway for completeness.

--
			Gleb.