KVM: x86/irq: Conditionally register IRQ bypass consumer again

As was attempted commit 14717e2 ("kvm: Conditionally register IRQ
bypass consumer"): "if we don't support a mechanism for bypassing IRQs,
don't register as a consumer.  Initially this applied to AMD processors,
but when AVIC support was implemented for assigned devices,
kvm_arch_has_irq_bypass() was always returning true.

We can still skip registering the consumer where enable_apicv
or posted-interrupts capability is unsupported or globally disabled.
This eliminates meaningless dev_info()s when the connect fails
between producer and consumer", such as on Linux hosts where enable_apicv
or posted-interrupts capability is unsupported or globally disabled.

Cc: Alex Williamson <alex.williamson@redhat.com>
Reported-by: Yong He <alexyonghe@tencent.com>
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=217379
Signed-off-by: Like Xu <likexu@tencent.com>
Message-Id: <20230724111236.76570-1-likexu@tencent.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Author: Like Xu

arch/x86/kvm/x86.c

@@ -13189,7 +13189,7 @@ EXPORT_SYMBOL_GPL(kvm_arch_has_noncoherent_dma);
 
 bool kvm_arch_has_irq_bypass(void)
 {
-	return true;
+	return enable_apicv && irq_remapping_cap(IRQ_POSTING_CAP);
 }
 
 int kvm_arch_irq_bypass_add_producer(struct irq_bypass_consumer *cons,