KVM: SVM: Don't update IRTEs if APICv/AVIC is disabled

Skip IRTE updates if AVIC is disabled/unsupported, as forcing the IRTE
into remapped mode (kvm_vcpu_apicv_active() will never be true) is
unnecessary and wasteful. The IOMMU driver is responsible for putting
IRTEs into remapped mode when an IRQ is allocated by a device, long before
that device is assigned to a VM. I.e. the kernel as a whole has major
issues if the IRTE isn't already in remapped mode.

Opportunsitically kvm_arch_has_irq_bypass() to query for APICv/AVIC, so
so that all checks in KVM x86 incorporate the same information.

Cc: Yosry Ahmed <[e-mail]>
Cc: Jim Mattson <[e-mail]>
Signed-off-by: Sean Christopherson <[e-mail]>
Message-ID: <[e-mail]>
Signed-off-by: Paolo Bonzini <[e-mail]>

arch/x86/kvm/svm/avic.c

···
 	struct kvm_irq_routing_table *irq_rt;
 	int idx, ret = 0;
 
-	if (!kvm_arch_has_assigned_device(kvm) ||
-	    !irq_remapping_cap(IRQ_POSTING_CAP))
+	if (!kvm_arch_has_assigned_device(kvm) || !kvm_arch_has_irq_bypass())
 		return 0;
 
 	pr_debug("SVM: %s: host_irq=%#x, guest_irq=%#x, set=%#x\n",