On Wed, Oct 3, 2018 at 10:42 AM, Sean Christopherson
<sean.j.christopherson@xxxxxxxxx> wrote:
> Query the flexpriority module param instead of simply checking if
> flexpriority is supported by the cpu when checking whether or not VMCS
> fields need to be updated in response to the guest changing its
> APIC_BASE MSR control bits. This avoids multiple unnecessary VMREADs
> and a VMWRITE if flexpriority is disabled via its module param and the
> cpu doesn't support X2APIC virtualization.
>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
> ---
>
> This is basically fixup for commit 76e97cc35522 ("KVM: VMX: check for
> existence of secondary exec controls before accessing") in
> kvm.git/queue. The aforementioned commit came from a series with a
> prior patch that removed the module param, but the prior patch was
> ultimately rejected resulting in this partially wrong code.
>
> arch/x86/kvm/vmx.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index c7ae8ea87bc4..612fd17be635 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -10223,7 +10223,7 @@ static void vmx_set_virtual_apic_mode(struct kvm_vcpu *vcpu)
> if (!lapic_in_kernel(vcpu))
> return;
>
> - if (!cpu_has_vmx_flexpriority() &&
> + if (!flexpriority_enabled &&
> !cpu_has_vmx_virtualize_x2apic_mode())
> return;
I think it would be better if cpu_has_vmx_flexpriority() returned
false when flexpriority_enabled is false.
