KVM: PPC: Book3S PR: Do not fail emulation with mtspr/mfspr for unknown SPRs

According to the PowerISA 2.07, mtspr and mfspr should not always
generate an illegal instruction exception when being used with an
undefined SPR, but rather treat the instruction as a NOP or inject a
privilege exception in some cases, too - depending on the SPR number.
Also turn the printk here into a ratelimited print statement, so that
the guest can not flood the dmesg log of the host by issueing lots of
illegal mtspr/mfspr instruction here.
Signed-off-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>

arch/powerpc/kvm/book3s_emulate.c

@@ -503,10 +503,18 @@ int kvmppc_core_emulate_mtspr_pr(struct kvm_vcpu *vcpu, int sprn, ulong spr_val)
 		break;
 unprivileged:
 	default:
-		printk(KERN_INFO "KVM: invalid SPR write: %d\n", sprn);
-#ifndef DEBUG_SPR
-		emulated = EMULATE_FAIL;
-#endif
+		pr_info_ratelimited("KVM: invalid SPR write: %d\n", sprn);
+		if (sprn & 0x10) {
+			if (kvmppc_get_msr(vcpu) & MSR_PR) {
+				kvmppc_core_queue_program(vcpu, SRR1_PROGPRIV);
+				emulated = EMULATE_AGAIN;
+			}
+		} else {
+			if ((kvmppc_get_msr(vcpu) & MSR_PR) || sprn == 0) {
+				kvmppc_core_queue_program(vcpu, SRR1_PROGILL);
+				emulated = EMULATE_AGAIN;
+			}
+		}
 		break;
 	}
 
@@ -648,10 +656,20 @@ int kvmppc_core_emulate_mfspr_pr(struct kvm_vcpu *vcpu, int sprn, ulong *spr_val
 		break;
 	default:
 unprivileged:
-		printk(KERN_INFO "KVM: invalid SPR read: %d\n", sprn);
-#ifndef DEBUG_SPR
-		emulated = EMULATE_FAIL;
-#endif
+		pr_info_ratelimited("KVM: invalid SPR read: %d\n", sprn);
+		if (sprn & 0x10) {
+			if (kvmppc_get_msr(vcpu) & MSR_PR) {
+				kvmppc_core_queue_program(vcpu, SRR1_PROGPRIV);
+				emulated = EMULATE_AGAIN;
+			}
+		} else {
+			if ((kvmppc_get_msr(vcpu) & MSR_PR) || sprn == 0 ||
+			    sprn == 4 || sprn == 5 || sprn == 6) {
+				kvmppc_core_queue_program(vcpu, SRR1_PROGILL);
+				emulated = EMULATE_AGAIN;
+			}
+		}
+
 		break;
 	}
 

arch/powerpc/kvm/emulate.c

@@ -259,10 +259,18 @@ int kvmppc_emulate_instruction(struct kvm_run *run, struct kvm_vcpu *vcpu)
 
 		case OP_31_XOP_MFSPR:
 			emulated = kvmppc_emulate_mfspr(vcpu, sprn, rt);
+			if (emulated == EMULATE_AGAIN) {
+				emulated = EMULATE_DONE;
+				advance = 0;
+			}
 			break;
 
 		case OP_31_XOP_MTSPR:
 			emulated = kvmppc_emulate_mtspr(vcpu, sprn, rs);
+			if (emulated == EMULATE_AGAIN) {
+				emulated = EMULATE_DONE;
+				advance = 0;
+			}
 			break;
 
 		case OP_31_XOP_TLBSYNC: