target/arm: kvm: Handle DABT with no valid ISS

On ARMv7 & ARMv8 some load/store instructions might trigger a data abort
exception with no valid ISS info to be decoded. The lack of decode info
makes it at least tricky to emulate those instruction which is one of the
(many) reasons why KVM will not even try to do so.

Add support for handling those by requesting KVM to inject external
dabt into the quest.

Signed-off-by: Beata Michalska <beata.michalska@linaro.org>
Reviewed-by: Andrew Jones <drjones@redhat.com>
Message-id: 20200629114110.30723-2-beata.michalska@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

diff --git a/target/arm/kvm.c b/target/arm/kvm.c
index 7c672c78b884fa9b043e93fe8e52a2345e1e6d89..3a46f54f1fde1be1142ab6d3b6b4c8983d844ad6 100644 (file)
--- a/target/arm/kvm.c
+++ b/target/arm/kvm.c
@@ -39,6 +39,7 @@ const KVMCapabilityInfo kvm_arch_required_capabilities[] = {
 
 static bool cap_has_mp_state;
 static bool cap_has_inject_serror_esr;
+static bool cap_has_inject_ext_dabt;
 
 static ARMHostCPUFeatures arm_host_cpu_features;
 
@@ -245,6 +246,16 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
         ret = -EINVAL;
     }
 
+    if (kvm_check_extension(s, KVM_CAP_ARM_NISV_TO_USER)) {
+        if (kvm_vm_enable_cap(s, KVM_CAP_ARM_NISV_TO_USER, 0)) {
+            error_report("Failed to enable KVM_CAP_ARM_NISV_TO_USER cap");
+        } else {
+            /* Set status for supporting the external dabt injection */
+            cap_has_inject_ext_dabt = kvm_check_extension(s,
+                                    KVM_CAP_ARM_INJECT_EXT_DABT);
+        }
+    }
+
     return ret;
 }
 
@@ -810,6 +821,42 @@ void kvm_arm_vm_state_change(void *opaque, int running, RunState state)
     }
 }
 
+/**
+ * kvm_arm_handle_dabt_nisv:
+ * @cs: CPUState
+ * @esr_iss: ISS encoding (limited) for the exception from Data Abort
+ *           ISV bit set to '0b0' -> no valid instruction syndrome
+ * @fault_ipa: faulting address for the synchronous data abort
+ *
+ * Returns: 0 if the exception has been handled, < 0 otherwise
+ */
+static int kvm_arm_handle_dabt_nisv(CPUState *cs, uint64_t esr_iss,
+                                    uint64_t fault_ipa)
+{
+    /*
+     * Request KVM to inject the external data abort into the guest
+     */
+    if (cap_has_inject_ext_dabt) {
+        struct kvm_vcpu_events events = { };
+        /*
+         * The external data abort event will be handled immediately by KVM
+         * using the address fault that triggered the exit on given VCPU.
+         * Requesting injection of the external data abort does not rely
+         * on any other VCPU state. Therefore, in this particular case, the VCPU
+         * synchronization can be exceptionally skipped.
+         */
+        events.exception.ext_dabt_pending = 1;
+        /* KVM_CAP_ARM_INJECT_EXT_DABT implies KVM_CAP_VCPU_EVENTS */
+        return kvm_vcpu_ioctl(cs, KVM_SET_VCPU_EVENTS, &events);
+    } else {
+        error_report("Data abort exception triggered by guest memory access "
+                     "at physical address: 0x"  TARGET_FMT_lx,
+                     (target_ulong)fault_ipa);
+        error_printf("KVM unable to emulate faulting instruction.\n");
+    }
+    return -1;
+}
+
 int kvm_arch_handle_exit(CPUState *cs, struct kvm_run *run)
 {
     int ret = 0;
@@ -820,6 +867,11 @@ int kvm_arch_handle_exit(CPUState *cs, struct kvm_run *run)
             ret = EXCP_DEBUG;
         } /* otherwise return to guest */
         break;
+    case KVM_EXIT_ARM_NISV:
+        /* External DABT with no valid iss to decode */
+        ret = kvm_arm_handle_dabt_nisv(cs, run->arm_nisv.esr_iss,
+                                       run->arm_nisv.fault_ipa);
+        break;
     default:
         qemu_log_mask(LOG_UNIMP, "%s: un-handled exit reason %d\n",
                       __func__, run->exit_reason);