kvm: x86: default legacy PCI device assignment support to "n"

VFIO has proved itself a much better option than KVM's built-in
device assignment.  It is mature, provides better isolation because
it enforces ACS, and even the userspace code is being tested on
a wider variety of hardware these days than the legacy support.

Disable legacy device assignment by default.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/Kconfig

@@ -88,13 +88,14 @@ config KVM_MMU_AUDIT
 config KVM_DEVICE_ASSIGNMENT
 	bool "KVM legacy PCI device assignment support"
 	depends on KVM && PCI && IOMMU_API
-	default y
+	default n
 	---help---
 	  Provide support for legacy PCI device assignment through KVM.  The
 	  kernel now also supports a full featured userspace device driver
-	  framework through VFIO, which supersedes much of this support.
+	  framework through VFIO, which supersedes this support and provides
+	  better security.
 
-	  If unsure, say Y.
+	  If unsure, say N.
 
 # OK, it's a little counter-intuitive to do this, but it puts it neatly under
 # the virtualization menu.