Re: [PATCH] KVM : Fix read/write to IA32_FEATURE_CONTROL MSR in nested virt

[Gleb Natapov <gleb@redhat.com>]

On Thu, Jul 04, 2013 at 03:21:15PM +0800, Arthur Chunqi Li wrote:
> On Thu, Jul 4, 2013 at 3:10 PM, Gleb Natapov <gleb@redhat.com> wrote:
> > On Thu, Jul 04, 2013 at 09:00:09AM +0200, Paolo Bonzini wrote:
> >> Il 03/07/2013 15:41, Arthur Chunqi Li ha scritto:
> >> > Fix read/write to IA32_FEATURE_CONTROL MSR in nested environment.
> >> > Simply return 0x5 when read and generate #GP(0) when write.
> >> > Delete handling codes in vmx_set_vmx_msr() and generate #GP(0) in
> >> > handle_wrmsr().
> >> >
> >> > Signed-off-by: Arthur Chunqi Li <yzt356@gmail.com>
> >> > ---
> >> >  arch/x86/kvm/vmx.c |    5 +----
> >> >  1 file changed, 1 insertion(+), 4 deletions(-)
> >> >
> >> > diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> >> > index 260a919..e125f94 100644
> >> > --- a/arch/x86/kvm/vmx.c
> >> > +++ b/arch/x86/kvm/vmx.c
> >> > @@ -2277,7 +2277,7 @@ static int vmx_get_vmx_msr(struct kvm_vcpu *vcpu, u32 msr_index, u64 *pdata)
> >> >
> >> >     switch (msr_index) {
> >> >     case MSR_IA32_FEATURE_CONTROL:
> >> > -           *pdata = 0;
> >> > +           *pdata = 0x5;
> >> >             break;
> >>
> >> This is not in the MSR_IA32_VMX_BASIC..MSR_IA32_VMX_TRUE_ENTRY_CTLS
> >> range, so you must check nested_vmx_allowed and return 0 if it is false.
> >>
> > Or 1?
> I think 1 is better here because this may return LOCK message when
> query and tell OS not to write (if OS does such logical check)
> >
> >> Otherwise looks good.
> >>
> >> Paolo
> >>
> >> >     case MSR_IA32_VMX_BASIC:
> >> >             /*
> >> > @@ -2356,9 +2356,6 @@ static int vmx_set_vmx_msr(struct kvm_vcpu *vcpu, u32 msr_index, u64 data)
> > Also this function is no longer needed. You can drop it.
> >
> > And what about Nadav's patch Bandan pointed too? It is not entirely
> > correct, but it is close to real HW.
> I think Nadav's patch is much closer to the HW scenario. However, I
> think we don't need make things complex since KVM doen't support SMX
> now and this MSR is always set to 0x5.
> 
Set to 0x5 by BIOS on real HW. This way BIOS can control if VMX is
exposed to an OS.

> Arthur
> >
> >> >     if (!nested_vmx_allowed(vcpu))
> >> >             return 0;
> >> >
> >> > -   if (msr_index == MSR_IA32_FEATURE_CONTROL)
> >> > -           /* TODO: the right thing. */
> >> > -           return 1;
> >> >     /*
> >> >      * No need to treat VMX capability MSRs specially: If we don't handle
> >> >      * them, handle_wrmsr will #GP(0), which is correct (they are readonly)
> >> >
> >
> > --
> >                         Gleb.

--
			Gleb.