target/arm: Implement ARMv8.1-PMU extension

The ARMv8.1-PMU extension requires:
* the evtCount field in PMETYPER<n>_EL0 is 16 bits, not 10
* MDCR_EL2.HPMD allows event counting to be disabled at EL2
* two new required events, STALL_FRONTEND and STALL_BACKEND
* ID register bits in ID_AA64DFR0_EL1 and ID_DFR0

We already implement the 16-bit evtCount field and the
HPMD bit, so all that is missing is the two new events:
STALL_FRONTEND
"counts every cycle counted by the CPU_CYCLES event on which no
operation was issued because there are no operations available
to issue to this PE from the frontend"
STALL_BACKEND
"counts every cycle counted by the CPU_CYCLES event on which no
operation was issued because the backend is unable to accept
any available operations from the frontend"

QEMU never stalls in this sense, so our implementation is trivial:
always return a zero count.

Backports commit 0727f63b1ecf765ebc48266f616f8fc362dc7fbc from qemu

qemu/target/arm/cpu.h

@@ -684,7 +684,7 @@ typedef struct CPUARMState {
      * should first be updated to something sparse instead of the current
      * supported_event_map[] array.
      */
-#define MAX_EVENT_ID 0x11
+#define MAX_EVENT_ID 0x24
     uint16_t supported_event_map[MAX_EVENT_ID + 1];
 
     // Unicorn engine

qemu/target/arm/helper.c

@@ -914,6 +914,13 @@ typedef struct pm_event {
      * counters hold a difference from the return value from this function
      */
     uint64_t (*get_count)(CPUARMState *);
+    /*
+     * Return how many nanoseconds it will take (at a minimum) for count events
+     * to occur. A negative value indicates the counter will never overflow, or
+     * that the counter has otherwise arranged for the overflow bit to be set
+     * and the PMU interrupt to be raised on overflow.
+     */
+    int64_t (*ns_per_count)(uint64_t);
 } pm_event;
 
 static bool event_always_supported(CPUARMState *env)
@@ -930,6 +937,11 @@ static uint64_t swinc_get_count(CPUARMState *env)
     return 0;
 }
 
+static int64_t swinc_ns_per(uint64_t ignored)
+{
+    return -1;
+}
+
 /*
  * Return the underlying cycle count for the PMU cycle counters. If we're in
  * usermode, simply return 0.
@@ -945,6 +957,11 @@ static uint64_t cycles_get_count(CPUARMState *env)
 }
 
 #ifndef CONFIG_USER_ONLY
+static int64_t cycles_ns_per(uint64_t cycles)
+{
+    return (ARM_CPU_FREQ / NANOSECONDS_PER_SECOND) * cycles;
+}
+
 static bool instructions_supported(CPUARMState *env)
 {
     return 0; /* Precise instruction counting */
@@ -956,25 +973,52 @@ static uint64_t instructions_get_count(CPUARMState *env)
 }
 #endif
 
+static bool pmu_8_1_events_supported(CPUARMState *env)
+{
+    /* For events which are supported in any v8.1 PMU */
+    return cpu_isar_feature(any_pmu_8_1, env_archcpu(env));
+}
+
+static uint64_t zero_event_get_count(CPUARMState *env)
+{
+    /* For events which on QEMU never fire, so their count is always zero */
+    return 0;
+}
+
+static int64_t zero_event_ns_per(uint64_t cycles)
+{
+    /* An event which never fires can never overflow */
+    return -1;
+}
 
 static const pm_event pm_events[] = {
-    {
-        0x000, /* SW_INCR */
-        event_always_supported,
-        swinc_get_count,
+    { .number = 0x000, /* SW_INCR */
+      .supported = event_always_supported,
+      .get_count = swinc_get_count,
+      .ns_per_count = swinc_ns_per,
     },
 #ifndef CONFIG_USER_ONLY
-    {
-        0x008, /* INST_RETIRED, Instruction architecturally executed */
-        instructions_supported,
-        instructions_get_count,
+    { .number = 0x008, /* INST_RETIRED, Instruction architecturally executed */
+      .supported = instructions_supported,
+      .get_count = instructions_get_count,
+      .ns_per_count = swinc_ns_per, /* UNICORN: Stubbed */
+    },
+    { .number = 0x011, /* CPU_CYCLES, Cycle */
+      .supported = event_always_supported,
+      .get_count = cycles_get_count,
+      .ns_per_count = cycles_ns_per,
     },
-    {
-        0x011, /* CPU_CYCLES, Cycle */
-        event_always_supported,
-        cycles_get_count,
-    }
 #endif
+    { .number = 0x023, /* STALL_FRONTEND */
+      .supported = pmu_8_1_events_supported,
+      .get_count = zero_event_get_count,
+      .ns_per_count = zero_event_ns_per,
+    },
+    { .number = 0x024, /* STALL_BACKEND */
+      .supported = pmu_8_1_events_supported,
+      .get_count = zero_event_get_count,
+      .ns_per_count = zero_event_ns_per,
+    },
 };
 
 #define UNSUPPORTED_EVENT UINT16_MAX