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);
