On Thu, Aug 20, 2020 at 02:43:56PM -0700, Jim Mattson wrote: > On Thu, Aug 20, 2020 at 6:34 AM Maxim Levitsky <mlevitsk@xxxxxxxxxx> wrote: > > > > This will be used later to return an error when setting this msr fails. > > > > For VMX, it already has an error condition when EFER is > > not in the shared MSR list, so return an error in this case. > > > > Signed-off-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx> > > --- > > > --- a/arch/x86/kvm/x86.c > > +++ b/arch/x86/kvm/x86.c > > @@ -1471,7 +1471,8 @@ static int set_efer(struct kvm_vcpu *vcpu, struct msr_data *msr_info) > > efer &= ~EFER_LMA; > > efer |= vcpu->arch.efer & EFER_LMA; > > > > - kvm_x86_ops.set_efer(vcpu, efer); > > + if (kvm_x86_ops.set_efer(vcpu, efer)) > > + return 1; > > This seems like a userspace ABI change to me. Previously, it looks > like userspace could always use KVM_SET_MSRS to set MSR_EFER to 0 or > EFER_SCE, and it would always succeed. Now, it looks like it will fail > on CPUs that don't support EFER in hardware. (Perhaps it should fail, > but it didn't before, AFAICT.) KVM emulates SYSCALL, presumably that also works when EFER doesn't exist in hardware. The above also adds weirdness to nested VMX as vmx_set_efer() simply can't fail.
