Re: [PATCH 03/17] KVM: monolithic: x86: handle the request_immediate_exit variation

Sean Christopherson
2019-09-23T22:35:29Z

On Fri, Sep 20, 2019 at 05:24:55PM -0400, Andrea Arcangeli wrote:
> request_immediate_exit is one of those few cases where the pointer to
> function of the method isn't fixed at build time and it requires
> special handling because hardware_setup() may override it at runtime.
>
> Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
> ---
> arch/x86/kvm/vmx/vmx_ops.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/vmx/vmx_ops.c b/arch/x86/kvm/vmx/vmx_ops.c
> index cdcad73935d9..25d441432901 100644
> --- a/arch/x86/kvm/vmx/vmx_ops.c
> +++ b/arch/x86/kvm/vmx/vmx_ops.c
> @@ -498,7 +498,10 @@ int kvm_x86_ops_check_nested_events(struct kvm_vcpu *vcpu, bool external_intr)
>
> void kvm_x86_ops_request_immediate_exit(struct kvm_vcpu *vcpu)
> {
> - vmx_request_immediate_exit(vcpu);
> + if (likely(enable_preemption_timer))
> + vmx_request_immediate_exit(vcpu);
> + else
> + __kvm_request_immediate_exit(vcpu);

Rather than wrap this in VMX code, what if we instead take advantage of a
monolithic module and add an inline to query enable_preemption_timer?
That'd likely save a few CALL/RET/JMP instructions and eliminate
__kvm_request_immediate_exit.

E.g. something like:

if (req_immediate_exit) {
kvm_make_request(KVM_REQ_EVENT, vcpu);
if (kvm_x86_has_request_immediate_exit())
kvm_x86_request_immediate_exit(vcpu);
else
smp_send_reschedule(vcpu->cpu);
}

> }
>
> void kvm_x86_ops_sched_in(struct kvm_vcpu *kvm, int cpu)