On Tue, 2020-09-29 at 14:26 +0200, Paolo Bonzini wrote:
> On 29/09/20 13:59, Qian Cai wrote:
> > WARN_ON_ONCE(!allow_smaller_maxphyaddr);
> >
> > I noticed the origin patch did not have this WARN_ON_ONCE(), but the
> > mainline
> > commit b96e6506c2ea ("KVM: x86: VMX: Make smaller physical guest address
> > space
> > support user-configurable") does have it for some reasons.
>
> Because that part of the code should not be reached. The exception
> bitmap is set up with
>
> if (!vmx_need_pf_intercept(vcpu))
> eb &= ~(1u << PF_VECTOR);
>
> where
>
> static inline bool vmx_need_pf_intercept(struct kvm_vcpu *vcpu)
> {
> if (!enable_ept)
> return true;
>
> return allow_smaller_maxphyaddr &&
> cpuid_maxphyaddr(vcpu) < boot_cpu_data.x86_phys_bits;
> }
>
> We shouldn't get here if "enable_ept && !allow_smaller_maxphyaddr",
> which implies vmx_need_pf_intercept(vcpu) == false. So the warning is
> genuine; I've sent a patch.
Care to provide a link to the patch? Just curious.
