KVM: PPC: Book3S PR: Enable use on POWER9 inside HPT-mode guests

This relaxes the restriction on using PR KVM on POWER9.  The existing
code does work inside a guest partition running in HPT mode, because
hypercalls such as H_ENTER use the old HPTE format, not the new
format used by POWER9, and so no change to PR KVM's HPT manipulation
code is required.  PR KVM will still refuse to run if the kernel is
using radix translation or if it is running bare-metal.
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>

arch/powerpc/kvm/book3s_pr.c

@@ -1735,9 +1735,16 @@ static void kvmppc_core_destroy_vm_pr(struct kvm *kvm)
 static int kvmppc_core_check_processor_compat_pr(void)
 {
 	/*
-	 * Disable KVM for Power9 untill the required bits merged.
+	 * PR KVM can work on POWER9 inside a guest partition
+	 * running in HPT mode.  It can't work if we are using
+	 * radix translation (because radix provides no way for
+	 * a process to have unique translations in quadrant 3)
+	 * or in a bare-metal HPT-mode host (because POWER9
+	 * uses a modified HPTE format which the PR KVM code
+	 * has not been adapted to use).
 	 */
-	if (cpu_has_feature(CPU_FTR_ARCH_300))
+	if (cpu_has_feature(CPU_FTR_ARCH_300) &&
+	    (radix_enabled() || cpu_has_feature(CPU_FTR_HVMODE)))
 		return -EIO;
 	return 0;
 }