Re: [PATCH 3/3] KVM: VMX: Use the canonical interface to read CR4.UMIP bit

[Sean Christopherson <seanjc@google.com>]

On Fri, Mar 31, 2023, Robert Hoo wrote:
> Sean Christopherson <seanjc@google.com> 于2023年3月11日周六 00:27写道：
> >
> > On Fri, Mar 10, 2023, Robert Hoo wrote:
> > > Use kvm_read_cr4_bits() rather than directly read vcpu->arch.cr4, now that
> > > we have reg cache layer and defined this wrapper.
> >
> > kvm_read_cr4_bits() predates this code by ~7 years.
> >
> > > Although, effectively for CR4.UMIP, it's the same, at present, as it's not
> > > guest owned, in case of future changes, here better to use the canonical
> > > interface.
> >
> > Practically speaking, UMIP _can't_ be guest owned without breaking UMIP emulation.
> > I do like not open coding vcpu->arch.cr4, but I don't particuarly like the changelog.
> >
> > This would also be a good time to opportunistically convert the WARN_ON() to a
> > WARN_ON_ONCE() (when it fires, it fires a _lot).
> >
> > This, with a reworded changelog?
> >
> >         /*
> >          * UMIP emulation relies on intercepting writes to CR4.UMIP, i.e. this
> >          * and other code needs to be updated if UMIP can be guest owned.
> >          */
> >         BUILD_BUG_ON(KVM_POSSIBLE_CR4_GUEST_BITS & X86_CR4_UMIP);
> >
> >         WARN_ON_ONCE(!kvm_read_cr4_bits(vcpu, X86_CR4_UMIP));
> >         return kvm_emulate_instruction(vcpu, 0);
> 
> Are you going to have this along with your "[PATCH] KVM: VMX: Treat
> UMIP as emulated if and only if the host doesn't have UMIP"?

Sure, I'll add a patch for that.