[PATCH v3] KVM: PPC: Book3S PR: Do not fail emulation with mtspr/mfspr for unknown SPRs

[Thomas Huth]

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 at redhat.com>
---
 v3:
 - Make sure that we do not advance the program counter after we've
   already changed it due to injecting a program interrupt

 v2:
 - Inject illegal instruction program interrupt instead of emulation
   assist interrupt (according to the last programming note in section
   6.5.9 of Book III of the PowerISA v2.07)

 arch/powerpc/kvm/book3s_emulate.c | 34 ++++++++++++++++++++++++++--------
 arch/powerpc/kvm/emulate.c        |  8 ++++++++
 2 files changed, 34 insertions(+), 8 deletions(-)

diff --git a/arch/powerpc/kvm/book3s_emulate.c b/arch/powerpc/kvm/book3s_emulate.c
index 8359752..68d6898 100644
--- a/arch/powerpc/kvm/book3s_emulate.c
+++ b/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;
 	}
 
diff --git a/arch/powerpc/kvm/emulate.c b/arch/powerpc/kvm/emulate.c
index b379146..c873ffe 100644
--- a/arch/powerpc/kvm/emulate.c
+++ b/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:
-- 
1.8.3.1