KVM: PPC: Emulate dcbf

commit d3286144 upstream.

Guests can trigger MMIO exits using dcbf. Since we don't emulate cache
incoherent MMIO, just do nothing and move on.
Reported-by: Ben Collins <ben.c@servergy.com>
Signed-off-by: Alexander Graf <agraf@suse.de>
Tested-by: Ben Collins <ben.c@servergy.com>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

arch/powerpc/kvm/emulate.c

@@ -35,6 +35,7 @@
 #define OP_TRAP_64 2
 
 #define OP_31_XOP_LWZX      23
+#define OP_31_XOP_DCBF      86
 #define OP_31_XOP_LBZX      87
 #define OP_31_XOP_STWX      151
 #define OP_31_XOP_STBX      215
@@ -370,6 +371,7 @@ int kvmppc_emulate_instruction(struct kvm_run *run, struct kvm_vcpu *vcpu)
 			kvmppc_set_exit_type(vcpu, EMULATED_MTSPR_EXITS);
 			break;
 
+		case OP_31_XOP_DCBF:
 		case OP_31_XOP_DCBI:
 			/* Do nothing. The guest is performing dcbi because
 			 * hardware DMA is not snooped by the dcache, but