KVM: x86: Rely solely on preempted_in_kernel flag for directed yield

Snapshot preempted_in_kernel using kvm_arch_vcpu_in_kernel() so that the
flag is "accurate" (or rather, consistent and deterministic within KVM)
for guests with protected state, and explicitly use preempted_in_kernel
when checking if a vCPU was preempted in kernel mode instead of bouncing
through kvm_arch_vcpu_in_kernel().

Drop the gnarly logic in kvm_arch_vcpu_in_kernel() that redirects to
preempted_in_kernel if the target vCPU is not the "running", i.e. loaded,
vCPU, as the only reason that code existed was for the directed yield case
where KVM wants to check the CPL of a vCPU that may or may not be loaded
on the current pCPU.

Cc: Like Xu <like.xu.linux@gmail.com>
Reviewed-by: Yuan Yao <yuan.yao@intel.com>
Link: https://lore.kernel.org/r/20240110003938.490206-3-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

Author: sean-jc

arch/x86/kvm/x86.c

@@ -5059,8 +5059,7 @@ void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
 	int idx;
 
 	if (vcpu->preempted) {
-		if (!vcpu->arch.guest_state_protected)
-			vcpu->arch.preempted_in_kernel = !static_call(kvm_x86_get_cpl)(vcpu);
+		vcpu->arch.preempted_in_kernel = kvm_arch_vcpu_in_kernel(vcpu);
 
 		/*
 		 * Take the srcu lock as memslots will be accessed to check the gfn
@@ -13056,7 +13055,7 @@ bool kvm_arch_dy_has_pending_interrupt(struct kvm_vcpu *vcpu)
 
 bool kvm_arch_vcpu_preempted_in_kernel(struct kvm_vcpu *vcpu)
 {
-	return kvm_arch_vcpu_in_kernel(vcpu);
+	return vcpu->arch.preempted_in_kernel;
 }
 
 bool kvm_arch_dy_runnable(struct kvm_vcpu *vcpu)
@@ -13079,9 +13078,6 @@ bool kvm_arch_vcpu_in_kernel(struct kvm_vcpu *vcpu)
 	if (vcpu->arch.guest_state_protected)
 		return true;
 
-	if (vcpu != kvm_get_running_vcpu())
-		return vcpu->arch.preempted_in_kernel;
-
 	return static_call(kvm_x86_get_cpl)(vcpu) == 0;
 }