Re: [PATCH 3/8] KVM: SVM: Sync cr0 and cr3 to kvm state before nested handling

Joerg Roedel
2010-04-23T14:17:30Z

On Fri, Apr 23, 2010 at 03:50:20PM +0200, Alexander Graf wrote:
>
> On 22.04.2010, at 12:33, Joerg Roedel wrote:
>
> > This patch syncs cr0 and cr3 from the vmcb to the kvm state
> > before nested intercept handling is done. This allows to
> > simplify the vmexit path.
> >
> > Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
> > ---
> > arch/x86/kvm/svm.c | 15 ++++++---------
> > 1 files changed, 6 insertions(+), 9 deletions(-)
> >
> > diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> > index c480d7f..5ad9d80 100644
> > --- a/arch/x86/kvm/svm.c
> > +++ b/arch/x86/kvm/svm.c
> > @@ -1799,10 +1799,7 @@ static int nested_svm_vmexit(struct vcpu_svm *svm)
> > nested_vmcb->save.gdtr = vmcb->save.gdtr;
> > nested_vmcb->save.idtr = vmcb->save.idtr;
> > nested_vmcb->save.cr0 = kvm_read_cr0(&svm->vcpu);
> > - if (npt_enabled)
> > - nested_vmcb->save.cr3 = vmcb->save.cr3;
> > - else
> > - nested_vmcb->save.cr3 = svm->vcpu.arch.cr3;
> > + nested_vmcb->save.cr3 = svm->vcpu.arch.cr3;
>
>
> Why don't we need this anymore again?

Because arch.cr3 contains always the current l2-cr3. This wasn't the
case before because the sync was done after the nested handling. But now
we do it before a vmexit can happen and are safe to just use arch.cr3.

Joerg