[PATCH v2 1/4] ppc/spapr: KVM FWNMI should not be enabled until guest requests it

[Nicholas Piggin <npiggin@gmail.com>]

The KVM FWNMI capability should be enabled with the "ibm,nmi-register"
rtas call. Although MCEs from KVM will be delivered as architected
interrupts to the guest before "ibm,nmi-register" is called, KVM has
different behaviour depending on whether the guest has enabled FWNMI
(it attempts to do more recovery on behalf of a non-FWNMI guest).

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
 hw/ppc/spapr_caps.c  | 7 ++++---
 hw/ppc/spapr_rtas.c  | 7 +++++++
 target/ppc/kvm.c     | 7 +++++++
 target/ppc/kvm_ppc.h | 6 ++++++
 4 files changed, 24 insertions(+), 3 deletions(-)

diff --git a/hw/ppc/spapr_caps.c b/hw/ppc/spapr_caps.c
index 679ae7959f..eb54f94227 100644
--- a/hw/ppc/spapr_caps.c
+++ b/hw/ppc/spapr_caps.c
@@ -517,9 +517,10 @@ static void cap_fwnmi_apply(SpaprMachineState *spapr, uint8_t val,
     }
 
     if (kvm_enabled()) {
-        if (kvmppc_set_fwnmi() < 0) {
-            error_setg(errp, "Firmware Assisted Non-Maskable Interrupts(FWNMI) "
-                             "not supported by KVM");
+        if (!kvmppc_get_fwnmi()) {
+            error_setg(errp,
+"Firmware Assisted Non-Maskable Interrupts(FWNMI) not supported by KVM.");
+            error_append_hint(errp, "Try appending -machine cap-fwnmi=off\n");
         }
     }
 }
diff --git a/hw/ppc/spapr_rtas.c b/hw/ppc/spapr_rtas.c
index 9fb8c8632a..29abe66d01 100644
--- a/hw/ppc/spapr_rtas.c
+++ b/hw/ppc/spapr_rtas.c
@@ -437,6 +437,13 @@ static void rtas_ibm_nmi_register(PowerPCCPU *cpu,
         return;
     }
 
+    if (kvm_enabled()) {
+        if (kvmppc_set_fwnmi() < 0) {
+            rtas_st(rets, 0, RTAS_OUT_NOT_SUPPORTED);
+            return;
+        }
+    }
+
     spapr->fwnmi_system_reset_addr = sreset_addr;
     spapr->fwnmi_machine_check_addr = mce_addr;
 
diff --git a/target/ppc/kvm.c b/target/ppc/kvm.c
index 597f72be1b..03d0667e8f 100644
--- a/target/ppc/kvm.c
+++ b/target/ppc/kvm.c
@@ -88,6 +88,7 @@ static int cap_ppc_safe_indirect_branch;
 static int cap_ppc_count_cache_flush_assist;
 static int cap_ppc_nested_kvm_hv;
 static int cap_large_decr;
+static int cap_fwnmi;
 
 static uint32_t debug_inst_opcode;
 
@@ -136,6 +137,7 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
     kvmppc_get_cpu_characteristics(s);
     cap_ppc_nested_kvm_hv = kvm_vm_check_extension(s, KVM_CAP_PPC_NESTED_HV);
     cap_large_decr = kvmppc_get_dec_bits();
+    cap_fwnmi = kvm_vm_check_extension(s, KVM_CAP_PPC_FWNMI);
     /*
      * Note: setting it to false because there is not such capability
      * in KVM at this moment.
@@ -2064,6 +2066,11 @@ void kvmppc_set_mpic_proxy(PowerPCCPU *cpu, int mpic_proxy)
     }
 }
 
+bool kvmppc_get_fwnmi(void)
+{
+    return cap_fwnmi;
+}
+
 int kvmppc_set_fwnmi(void)
 {
     PowerPCCPU *cpu = POWERPC_CPU(first_cpu);
diff --git a/target/ppc/kvm_ppc.h b/target/ppc/kvm_ppc.h
index 332fa0aa1c..fcaf745516 100644
--- a/target/ppc/kvm_ppc.h
+++ b/target/ppc/kvm_ppc.h
@@ -27,6 +27,7 @@ void kvmppc_enable_h_page_init(void);
 void kvmppc_set_papr(PowerPCCPU *cpu);
 int kvmppc_set_compat(PowerPCCPU *cpu, uint32_t compat_pvr);
 void kvmppc_set_mpic_proxy(PowerPCCPU *cpu, int mpic_proxy);
+bool kvmppc_get_fwnmi(void);
 int kvmppc_set_fwnmi(void);
 int kvmppc_smt_threads(void);
 void kvmppc_error_append_smt_possible_hint(Error *const *errp);
@@ -163,6 +164,11 @@ static inline void kvmppc_set_mpic_proxy(PowerPCCPU *cpu, int mpic_proxy)
 {
 }
 
+static inline bool kvmppc_get_fwnmi(void)
+{
+    return false;
+}
+
 static inline int kvmppc_set_fwnmi(void)
 {
     return -1;
-- 
2.23.0