Re: [PATCH 2/5] KVM: SVM: check validity of VMCB when returning from SMM

[Sean Christopherson <seanjc@google.com>]

On Tue, Mar 10, 2026, Yosry Ahmed wrote:
> > Cc: stable@vger.kernel.org
> > Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> > ---
> >  arch/x86/kvm/svm/nested.c | 12 ++++++++++--
> >  arch/x86/kvm/svm/svm.c    |  4 ++++
> >  arch/x86/kvm/svm/svm.h    |  1 +
> >  3 files changed, 15 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
> > index 7b61124051a7..de9906adb73b 100644
> > --- a/arch/x86/kvm/svm/nested.c
> > +++ b/arch/x86/kvm/svm/nested.c
> > @@ -419,6 +419,15 @@ static bool nested_vmcb_check_controls(struct kvm_vcpu *vcpu)
> >         return __nested_vmcb_check_controls(vcpu, ctl);
> >  }
> >
> > +int nested_svm_check_cached_vmcb12(struct kvm_vcpu *vcpu)
> > +{
> > +       if (!nested_vmcb_check_save(vcpu) ||
> > +           !nested_vmcb_check_controls(vcpu))
> > +               return -EINVAL;
> > +
> > +       return 0;
> > +}
> 
> Nit: if we make this a boolean we could just do:
> 
> bool nested_svm_check_cached_vmcb12(struct kvm_vcpu *vcpu)
> {
>        return nested_vmcb_check_save(vcpu) && nested_vmcb_check_controls(vcpu);

I don't care one way or the other for this particular patch, but once the dust
settles on nSVM (assuming it ever does) I do think we should align the "nested
check" return types across nVMX and nSVM (which is likely why Paolo ended up with
the above; I requested using -EINVAL for the nVMXx) patch.

My fairly strong preference is to use 0/-errno as "return -EINVAL" is more
obviously an error than "return true".  But we can bikeshed later :-)