target/riscv: Support mcycle/minstret write operation

mcycle/minstret are actually WARL registers and can be written with any
given value. With SBI PMU extension, it will be used to store a initial
value provided from supervisor OS. The Qemu also need prohibit the counter
increment if mcountinhibit is set.

Support mcycle/minstret through generic counter infrastructure.

Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Signed-off-by: Atish Patra <atish.patra@wdc.com>
Signed-off-by: Atish Patra <atishp@rivosinc.com>
Message-Id: <20220620231603.2547260-8-atishp@rivosinc.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

target/riscv/cpu.h

@@ -117,7 +117,7 @@ typedef struct CPUArchState CPURISCVState;
 #endif
 
 #define RV_VLEN_MAX 1024
-#define RV_MAX_MHPMEVENTS 29
+#define RV_MAX_MHPMEVENTS 32
 #define RV_MAX_MHPMCOUNTERS 32
 
 FIELD(VTYPE, VLMUL, 0, 3)
@@ -127,6 +127,18 @@ FIELD(VTYPE, VMA, 7, 1)
 FIELD(VTYPE, VEDIV, 8, 2)
 FIELD(VTYPE, RESERVED, 10, sizeof(target_ulong) * 8 - 11)
 
+typedef struct PMUCTRState {
+    /* Current value of a counter */
+    target_ulong mhpmcounter_val;
+    /* Current value of a counter in RV32*/
+    target_ulong mhpmcounterh_val;
+    /* Snapshot values of counter */
+    target_ulong mhpmcounter_prev;
+    /* Snapshort value of a counter in RV32 */
+    target_ulong mhpmcounterh_prev;
+    bool started;
+} PMUCTRState;
+
 struct CPUArchState {
     target_ulong gpr[32];
     target_ulong gprh[32]; /* 64 top bits of the 128-bit registers */
@@ -279,13 +291,10 @@ struct CPUArchState {
 
     target_ulong mcountinhibit;
 
-    /* PMU counter configured values */
+    /* PMU counter state */
-    target_ulong mhpmcounter_val[RV_MAX_MHPMCOUNTERS];
+    PMUCTRState pmu_ctrs[RV_MAX_MHPMCOUNTERS];
 
-    /* for RV32 */
+    /* PMU event selector configured values. First three are unused*/
-    target_ulong mhpmcounterh_val[RV_MAX_MHPMCOUNTERS];
-
-    /* PMU event selector configured values */
     target_ulong mhpmevent_val[RV_MAX_MHPMEVENTS];
 
     target_ulong sscratch;

target/riscv/csr.c

@@ -21,6 +21,7 @@
 #include "qemu/log.h"
 #include "qemu/timer.h"
 #include "cpu.h"
+#include "pmu.h"
 #include "qemu/main-loop.h"
 #include "exec/exec-all.h"
 #include "sysemu/cpu-timers.h"
@@ -597,34 +598,28 @@ static int write_vcsr(CPURISCVState *env, int csrno, target_ulong val)
 }
 
 /* User Timers and Counters */
-static RISCVException read_instret(CPURISCVState *env, int csrno,
+static target_ulong get_ticks(bool shift)
-                                   target_ulong *val)
 {
-#if !defined(CONFIG_USER_ONLY)
+    int64_t val;
-    if (icount_enabled()) {
+    target_ulong result;
-        *val = icount_get();
-    } else {
-        *val = cpu_get_host_ticks();
-    }
-#else
-    *val = cpu_get_host_ticks();
-#endif
-    return RISCV_EXCP_NONE;
-}
 
-static RISCVException read_instreth(CPURISCVState *env, int csrno,
-                                    target_ulong *val)
-{
 #if !defined(CONFIG_USER_ONLY)
     if (icount_enabled()) {
-        *val = icount_get() >> 32;
+        val = icount_get();
     } else {
-        *val = cpu_get_host_ticks() >> 32;
+        val = cpu_get_host_ticks();
     }
 #else
-    *val = cpu_get_host_ticks() >> 32;
+    val = cpu_get_host_ticks();
 #endif
-    return RISCV_EXCP_NONE;
+
+    if (shift) {
+        result = val >> 32;
+    } else {
+        result = val;
+    }
+
+    return result;
 }
 
 #if defined(CONFIG_USER_ONLY)
@@ -642,11 +637,23 @@ static RISCVException read_timeh(CPURISCVState *env, int csrno,
     return RISCV_EXCP_NONE;
 }
 
+static int read_hpmcounter(CPURISCVState *env, int csrno, target_ulong *val)
+{
+    *val = get_ticks(false);
+    return RISCV_EXCP_NONE;
+}
+
+static int read_hpmcounterh(CPURISCVState *env, int csrno, target_ulong *val)
+{
+    *val = get_ticks(true);
+    return RISCV_EXCP_NONE;
+}
+
 #else /* CONFIG_USER_ONLY */
 
 static int read_mhpmevent(CPURISCVState *env, int csrno, target_ulong *val)
 {
-    int evt_index = csrno - CSR_MHPMEVENT3;
+    int evt_index = csrno - CSR_MCOUNTINHIBIT;
 
     *val = env->mhpmevent_val[evt_index];
 
@@ -655,7 +662,7 @@ static int read_mhpmevent(CPURISCVState *env, int csrno, target_ulong *val)
 
 static int write_mhpmevent(CPURISCVState *env, int csrno, target_ulong val)
 {
-    int evt_index = csrno - CSR_MHPMEVENT3;
+    int evt_index = csrno - CSR_MCOUNTINHIBIT;
 
     env->mhpmevent_val[evt_index] = val;
 
@@ -664,55 +671,105 @@ static int write_mhpmevent(CPURISCVState *env, int csrno, target_ulong val)
 
 static int write_mhpmcounter(CPURISCVState *env, int csrno, target_ulong val)
 {
-    int ctr_index = csrno - CSR_MHPMCOUNTER3 + 3;
+    int ctr_idx = csrno - CSR_MCYCLE;
+    PMUCTRState *counter = &env->pmu_ctrs[ctr_idx];
 
-    env->mhpmcounter_val[ctr_index] = val;
+    counter->mhpmcounter_val = val;
+    if (riscv_pmu_ctr_monitor_cycles(env, ctr_idx) ||
+        riscv_pmu_ctr_monitor_instructions(env, ctr_idx)) {
+        counter->mhpmcounter_prev = get_ticks(false);
+    } else {
+        /* Other counters can keep incrementing from the given value */
+        counter->mhpmcounter_prev = val;
+    }
 
     return RISCV_EXCP_NONE;
 }
 
 static int write_mhpmcounterh(CPURISCVState *env, int csrno, target_ulong val)
 {
-    int ctr_index = csrno - CSR_MHPMCOUNTER3H + 3;
+    int ctr_idx = csrno - CSR_MCYCLEH;
+    PMUCTRState *counter = &env->pmu_ctrs[ctr_idx];
 
-    env->mhpmcounterh_val[ctr_index] = val;
+    counter->mhpmcounterh_val = val;
+    if (riscv_pmu_ctr_monitor_cycles(env, ctr_idx) ||
+        riscv_pmu_ctr_monitor_instructions(env, ctr_idx)) {
+        counter->mhpmcounterh_prev = get_ticks(true);
+    } else {
+        counter->mhpmcounterh_prev = val;
+    }
+
+    return RISCV_EXCP_NONE;
+}
+
+static RISCVException riscv_pmu_read_ctr(CPURISCVState *env, target_ulong *val,
+                                         bool upper_half, uint32_t ctr_idx)
+{
+    PMUCTRState counter = env->pmu_ctrs[ctr_idx];
+    target_ulong ctr_prev = upper_half ? counter.mhpmcounterh_prev :
+                                         counter.mhpmcounter_prev;
+    target_ulong ctr_val = upper_half ? counter.mhpmcounterh_val :
+                                        counter.mhpmcounter_val;
+
+    if (get_field(env->mcountinhibit, BIT(ctr_idx))) {
+        /**
+         * Counter should not increment if inhibit bit is set. We can't really
+         * stop the icount counting. Just return the counter value written by
+         * the supervisor to indicate that counter was not incremented.
+         */
+        if (!counter.started) {
+            *val = ctr_val;
+            return RISCV_EXCP_NONE;
+        } else {
+            /* Mark that the counter has been stopped */
+            counter.started = false;
+        }
+    }
+
+    /**
+     * The kernel computes the perf delta by subtracting the current value from
+     * the value it initialized previously (ctr_val).
+     */
+    if (riscv_pmu_ctr_monitor_cycles(env, ctr_idx) ||
+        riscv_pmu_ctr_monitor_instructions(env, ctr_idx)) {
+        *val = get_ticks(upper_half) - ctr_prev + ctr_val;
+    } else {
+        *val = ctr_val;
+    }
 
     return RISCV_EXCP_NONE;
 }
 
 static int read_hpmcounter(CPURISCVState *env, int csrno, target_ulong *val)
 {
-    int ctr_index;
+    uint16_t ctr_index;
 
     if (csrno >= CSR_MCYCLE && csrno <= CSR_MHPMCOUNTER31) {
-        ctr_index = csrno - CSR_MHPMCOUNTER3 + 3;
+        ctr_index = csrno - CSR_MCYCLE;
     } else if (csrno >= CSR_CYCLE && csrno <= CSR_HPMCOUNTER31) {
-        ctr_index = csrno - CSR_HPMCOUNTER3 + 3;
+        ctr_index = csrno - CSR_CYCLE;
     } else {
         return RISCV_EXCP_ILLEGAL_INST;
     }
-    *val = env->mhpmcounter_val[ctr_index];
 
-    return RISCV_EXCP_NONE;
+    return riscv_pmu_read_ctr(env, val, false, ctr_index);
 }
 
 static int read_hpmcounterh(CPURISCVState *env, int csrno, target_ulong *val)
 {
-    int ctr_index;
+    uint16_t ctr_index;
 
     if (csrno >= CSR_MCYCLEH && csrno <= CSR_MHPMCOUNTER31H) {
-        ctr_index = csrno - CSR_MHPMCOUNTER3H + 3;
+        ctr_index = csrno - CSR_MCYCLEH;
     } else if (csrno >= CSR_CYCLEH && csrno <= CSR_HPMCOUNTER31H) {
-        ctr_index = csrno - CSR_HPMCOUNTER3H + 3;
+        ctr_index = csrno - CSR_CYCLEH;
     } else {
         return RISCV_EXCP_ILLEGAL_INST;
     }
-    *val = env->mhpmcounterh_val[ctr_index];
 
-    return RISCV_EXCP_NONE;
+    return riscv_pmu_read_ctr(env, val, true, ctr_index);
 }
 
-
 static RISCVException read_time(CPURISCVState *env, int csrno,
                                 target_ulong *val)
 {
@@ -1567,11 +1624,23 @@ static RISCVException read_mcountinhibit(CPURISCVState *env, int csrno,
 static RISCVException write_mcountinhibit(CPURISCVState *env, int csrno,
                                           target_ulong val)
 {
+    int cidx;
+    PMUCTRState *counter;
+
     if (env->priv_ver < PRIV_VERSION_1_11_0) {
         return RISCV_EXCP_ILLEGAL_INST;
     }
 
     env->mcountinhibit = val;
+
+    /* Check if any other counter is also monitoring cycles/instructions */
+    for (cidx = 0; cidx < RV_MAX_MHPMCOUNTERS; cidx++) {
+        if (!get_field(env->mcountinhibit, BIT(cidx))) {
+            counter = &env->pmu_ctrs[cidx];
+            counter->started = true;
+        }
+    }
+
     return RISCV_EXCP_NONE;
 }
 
@@ -3533,10 +3602,10 @@ riscv_csr_operations csr_ops[CSR_TABLE_SIZE] = {
     [CSR_VLENB]    = { "vlenb",    vs,    read_vlenb,
                                           .min_priv_ver = PRIV_VERSION_1_12_0 },
     /* User Timers and Counters */
-    [CSR_CYCLE]    = { "cycle",    ctr,    read_instret  },
+    [CSR_CYCLE]    = { "cycle",    ctr,    read_hpmcounter  },
-    [CSR_INSTRET]  = { "instret",  ctr,    read_instret  },
+    [CSR_INSTRET]  = { "instret",  ctr,    read_hpmcounter  },
-    [CSR_CYCLEH]   = { "cycleh",   ctr32,  read_instreth },
+    [CSR_CYCLEH]   = { "cycleh",   ctr32,  read_hpmcounterh },
-    [CSR_INSTRETH] = { "instreth", ctr32,  read_instreth },
+    [CSR_INSTRETH] = { "instreth", ctr32,  read_hpmcounterh },
 
     /*
      * In privileged mode, the monitor will have to emulate TIME CSRs only if
@@ -3550,10 +3619,10 @@ riscv_csr_operations csr_ops[CSR_TABLE_SIZE] = {
 
 #if !defined(CONFIG_USER_ONLY)
     /* Machine Timers and Counters */
-    [CSR_MCYCLE]    = { "mcycle",    any,   read_instret  },
+    [CSR_MCYCLE]    = { "mcycle",    any,   read_hpmcounter, write_mhpmcounter},
-    [CSR_MINSTRET]  = { "minstret",  any,   read_instret  },
+    [CSR_MINSTRET]  = { "minstret",  any,   read_hpmcounter, write_mhpmcounter},
-    [CSR_MCYCLEH]   = { "mcycleh",   any32, read_instreth },
+    [CSR_MCYCLEH]   = { "mcycleh",   any32, read_hpmcounterh, write_mhpmcounterh},
-    [CSR_MINSTRETH] = { "minstreth", any32, read_instreth },
+    [CSR_MINSTRETH] = { "minstreth", any32, read_hpmcounterh, write_mhpmcounterh},
 
     /* Machine Information Registers */
     [CSR_MVENDORID] = { "mvendorid", any,   read_mvendorid },

target/riscv/machine.c

@@ -279,7 +279,28 @@ static const VMStateDescription vmstate_envcfg = {
         VMSTATE_UINT64(env.menvcfg, RISCVCPU),
         VMSTATE_UINTTL(env.senvcfg, RISCVCPU),
         VMSTATE_UINT64(env.henvcfg, RISCVCPU),
+        VMSTATE_END_OF_LIST()
+    }
+};
 
+static bool pmu_needed(void *opaque)
+{
+    RISCVCPU *cpu = opaque;
+
+    return cpu->cfg.pmu_num;
+}
+
+static const VMStateDescription vmstate_pmu_ctr_state = {
+    .name = "cpu/pmu",
+    .version_id = 1,
+    .minimum_version_id = 1,
+    .needed = pmu_needed,
+    .fields = (VMStateField[]) {
+        VMSTATE_UINTTL(mhpmcounter_val, PMUCTRState),
+        VMSTATE_UINTTL(mhpmcounterh_val, PMUCTRState),
+        VMSTATE_UINTTL(mhpmcounter_prev, PMUCTRState),
+        VMSTATE_UINTTL(mhpmcounterh_prev, PMUCTRState),
+        VMSTATE_BOOL(started, PMUCTRState),
         VMSTATE_END_OF_LIST()
     }
 };
@@ -331,8 +352,8 @@ const VMStateDescription vmstate_riscv_cpu = {
         VMSTATE_UINTTL(env.scounteren, RISCVCPU),
         VMSTATE_UINTTL(env.mcounteren, RISCVCPU),
         VMSTATE_UINTTL(env.mcountinhibit, RISCVCPU),
-        VMSTATE_UINTTL_ARRAY(env.mhpmcounter_val, RISCVCPU, RV_MAX_MHPMCOUNTERS),
+        VMSTATE_STRUCT_ARRAY(env.pmu_ctrs, RISCVCPU, RV_MAX_MHPMCOUNTERS, 0,
-        VMSTATE_UINTTL_ARRAY(env.mhpmcounterh_val, RISCVCPU, RV_MAX_MHPMCOUNTERS),
+                             vmstate_pmu_ctr_state, PMUCTRState),
         VMSTATE_UINTTL_ARRAY(env.mhpmevent_val, RISCVCPU, RV_MAX_MHPMEVENTS),
         VMSTATE_UINTTL(env.sscratch, RISCVCPU),
         VMSTATE_UINTTL(env.mscratch, RISCVCPU),

target/riscv/meson.build

@@ -30,7 +30,8 @@ riscv_softmmu_ss.add(files(
   'pmp.c',
   'debug.c',
   'monitor.c',
-  'machine.c'
+  'machine.c',
+  'pmu.c'
 ))
 
 target_arch += {'riscv': riscv_ss}

target/riscv/pmu.c

@@ -0,0 +1,32 @@
+/*
+ * RISC-V PMU file.
+ *
+ * Copyright (c) 2021 Western Digital Corporation or its affiliates.
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2 or later, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "qemu/osdep.h"
+#include "cpu.h"
+#include "pmu.h"
+
+bool riscv_pmu_ctr_monitor_instructions(CPURISCVState *env,
+                                        uint32_t target_ctr)
+{
+    return (target_ctr == 0) ? true : false;
+}
+
+bool riscv_pmu_ctr_monitor_cycles(CPURISCVState *env, uint32_t target_ctr)
+{
+    return (target_ctr == 2) ? true : false;
+}

target/riscv/pmu.h

@@ -0,0 +1,28 @@
+/*
+ * RISC-V PMU header file.
+ *
+ * Copyright (c) 2021 Western Digital Corporation or its affiliates.
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2 or later, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "qemu/osdep.h"
+#include "qemu/log.h"
+#include "cpu.h"
+#include "qemu/main-loop.h"
+#include "exec/exec-all.h"
+
+bool riscv_pmu_ctr_monitor_instructions(CPURISCVState *env,
+                                        uint32_t target_ctr);
+bool riscv_pmu_ctr_monitor_cycles(CPURISCVState *env,
+                                  uint32_t target_ctr);