On Wed, Oct 03, 2018 at 11:32:33AM -0700, Jim Mattson wrote:
> 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.
Ha, I had that all coded up but decided against it because the
convention used by other module params is to not adjust cpu_has_*().
