From: Sean Christopherson seanjc@google.com Sent: Wednesday, December 29, 2021 8:10 AM
But why even bother with an extra flag? Can't vmx_update_exception_bitmap() get the guest's MSR_IA32_XFD value and intercept #NM accordingly? Then you could even handle this fully in kvm_set_msr_common(), e.g.
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 2c9606380bca..c6c936d2b298 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -3704,6 +3704,8 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info) return 1;
fpu_update_guest_xfd(&vcpu->arch.guest_fpu, data);
/* Blah blah blah blah */static_call(kvm_x86_update_exception_bitmap)(vcpu); break;
btw follow Paolo's suggestion here:
https://lore.kernel.org/all/6e95b6f7-44dc-7e48-4e6e-81cf85fc11c6@redhat.com/
He prefers to disabling xfd interception in vmx specific code instead of introducing a new callback to be called in common code. Since we want to always trap #NM after xfd interception is disabled (which is done after calling the msr common code), it also reads cleaner to call update_exception_bitmap() from vmx.c instead of here.
Thanks Kevin