[Qemu-devel] [QEMU-PPC] [PATCH 2/4] target/ppc: Implement large decrementer support for TCG

[Suraj Jitindar Singh <sjitindarsingh@gmail.com>]

Prior to POWER9 the decrementer was a 32-bit register which decremented
with each tick of the timebase. From POWER9 onwards the decrementer can
be set to operate in a mode called large decrementer where it acts as a
n-bit decrementing register which is visible as a 64-bit register, that
is the value of the decrementer is sign extended to 64 bits (where n is
implementation dependant).

The mode in which the decrementer operates is controlled by the LPCR_LD
bit in the logical paritition control register (LPCR).

>From POWER9 onwards the HDEC (hypervisor decrementer) was enlarged to
h-bits, also sign extended to 64 bits (where h is implementation
dependant). Note this isn't configurable and is always enabled.

For TCG we allow the user to configure a custom large decrementer size,
so long as it's at least 32 and less than the size of the HDEC (the
restrictions imposed by the ISA).

Signed-off-by: Suraj Jitindar Singh <sjitindarsingh@gmail.com>
Signed-off-by: Cédric Le Goater <clg@kaod.org>
---
 hw/ppc/ppc.c                    | 78 ++++++++++++++++++++++++++++-------------
 hw/ppc/spapr.c                  |  8 +++++
 hw/ppc/spapr_caps.c             | 38 +++++++++++++++++++-
 target/ppc/cpu-qom.h            |  1 +
 target/ppc/cpu.h                | 11 +++---
 target/ppc/mmu-hash64.c         |  2 +-
 target/ppc/translate.c          |  2 +-
 target/ppc/translate_init.inc.c |  1 +
 8 files changed, 109 insertions(+), 32 deletions(-)

diff --git a/hw/ppc/ppc.c b/hw/ppc/ppc.c
index d1e3d4cd20..853afeed6a 100644
--- a/hw/ppc/ppc.c
+++ b/hw/ppc/ppc.c
@@ -744,10 +744,10 @@ bool ppc_decr_clear_on_delivery(CPUPPCState *env)
     return ((tb_env->flags & flags) == PPC_DECR_UNDERFLOW_TRIGGERED);
 }
 
-static inline uint32_t _cpu_ppc_load_decr(CPUPPCState *env, uint64_t next)
+static inline uint64_t _cpu_ppc_load_decr(CPUPPCState *env, uint64_t next)
 {
     ppc_tb_t *tb_env = env->tb_env;
-    uint32_t decr;
+    uint64_t decr;
     int64_t diff;
 
     diff = next - qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
@@ -758,27 +758,42 @@ static inline uint32_t _cpu_ppc_load_decr(CPUPPCState *env, uint64_t next)
     }  else {
         decr = -muldiv64(-diff, tb_env->decr_freq, NANOSECONDS_PER_SECOND);
     }
-    LOG_TB("%s: %08" PRIx32 "\n", __func__, decr);
+    LOG_TB("%s: %016" PRIx64 "\n", __func__, decr);
 
     return decr;
 }
 
-uint32_t cpu_ppc_load_decr (CPUPPCState *env)
+target_ulong cpu_ppc_load_decr (CPUPPCState *env)
 {
     ppc_tb_t *tb_env = env->tb_env;
+    uint64_t decr;
 
     if (kvm_enabled()) {
         return env->spr[SPR_DECR];
     }
 
-    return _cpu_ppc_load_decr(env, tb_env->decr_next);
+    decr = _cpu_ppc_load_decr(env, tb_env->decr_next);
+
+    /*
+     * If large decrementer is enabled then the decrementer is signed extened
+     * to 64 bits, otherwise it is a 32 bit value.
+     */
+    if (env->spr[SPR_LPCR] & LPCR_LD)
+        return decr;
+    return (uint32_t) decr;
 }
 
-uint32_t cpu_ppc_load_hdecr (CPUPPCState *env)
+target_ulong cpu_ppc_load_hdecr (CPUPPCState *env)
 {
     ppc_tb_t *tb_env = env->tb_env;
+    uint64_t decr;
 
-    return _cpu_ppc_load_decr(env, tb_env->hdecr_next);
+    decr =  _cpu_ppc_load_decr(env, tb_env->hdecr_next);
+
+    /* If POWER9 or later then hdecr is sign extended to 64 bits otherwise 32 */
+    if (env->mmu_model & POWERPC_MMU_3_00)
+        return decr;
+    return (uint32_t) decr;
 }
 
 uint64_t cpu_ppc_load_purr (CPUPPCState *env)
@@ -832,13 +847,21 @@ static void __cpu_ppc_store_decr(PowerPCCPU *cpu, uint64_t *nextp,
                                  QEMUTimer *timer,
                                  void (*raise_excp)(void *),
                                  void (*lower_excp)(PowerPCCPU *),
-                                 uint32_t decr, uint32_t value)
+                                 target_ulong decr, target_ulong value,
+                                 int nr_bits)
 {
     CPUPPCState *env = &cpu->env;
     ppc_tb_t *tb_env = env->tb_env;
     uint64_t now, next;
+    bool negative;
+
+    /* Truncate value to decr_width and sign extend for simplicity */
+    value &= ((1ULL << nr_bits) - 1);
+    negative = !!(value & (1ULL << (nr_bits - 1)));
+    if (negative)
+        value |= (0xFFFFFFFFULL << nr_bits);
 
-    LOG_TB("%s: %08" PRIx32 " => %08" PRIx32 "\n", __func__,
+    LOG_TB("%s: " TARGET_FMT_lx " => " TARGET_FMT_lx "\n", __func__,
                 decr, value);
 
     if (kvm_enabled()) {
@@ -860,15 +883,15 @@ static void __cpu_ppc_store_decr(PowerPCCPU *cpu, uint64_t *nextp,
      * an edge interrupt, so raise it here too.
      */
     if ((value < 3) ||
-        ((tb_env->flags & PPC_DECR_UNDERFLOW_LEVEL) && (value & 0x80000000)) ||
-        ((tb_env->flags & PPC_DECR_UNDERFLOW_TRIGGERED) && (value & 0x80000000)
-          && !(decr & 0x80000000))) {
+        ((tb_env->flags & PPC_DECR_UNDERFLOW_LEVEL) && negative) ||
+        ((tb_env->flags & PPC_DECR_UNDERFLOW_TRIGGERED) && negative
+          && !(decr & (1ULL << (nr_bits - 1))))) {
         (*raise_excp)(cpu);
         return;
     }
 
     /* On MSB level based systems a 0 for the MSB stops interrupt delivery */
-    if (!(value & 0x80000000) && (tb_env->flags & PPC_DECR_UNDERFLOW_LEVEL)) {
+    if (!negative && (tb_env->flags & PPC_DECR_UNDERFLOW_LEVEL)) {
         (*lower_excp)(cpu);
     }
 
@@ -881,21 +904,24 @@ static void __cpu_ppc_store_decr(PowerPCCPU *cpu, uint64_t *nextp,
     timer_mod(timer, next);
 }
 
-static inline void _cpu_ppc_store_decr(PowerPCCPU *cpu, uint32_t decr,
-                                       uint32_t value)
+static inline void _cpu_ppc_store_decr(PowerPCCPU *cpu, target_ulong decr,
+                                       target_ulong value, int nr_bits)
 {
     ppc_tb_t *tb_env = cpu->env.tb_env;
 
     __cpu_ppc_store_decr(cpu, &tb_env->decr_next, tb_env->decr_timer,
                          tb_env->decr_timer->cb, &cpu_ppc_decr_lower, decr,
-                         value);
+                         value, nr_bits);
 }
 
-void cpu_ppc_store_decr (CPUPPCState *env, uint32_t value)
+void cpu_ppc_store_decr (CPUPPCState *env, target_ulong value)
 {
     PowerPCCPU *cpu = ppc_env_get_cpu(env);
+    int nr_bits = 32;
+    if ((env->spr[SPR_LPCR] & LPCR_LD) && (env->large_decr_bits > 32))
+        nr_bits = env->large_decr_bits;
 
-    _cpu_ppc_store_decr(cpu, cpu_ppc_load_decr(env), value);
+    _cpu_ppc_store_decr(cpu, cpu_ppc_load_decr(env), value, nr_bits);
 }
 
 static void cpu_ppc_decr_cb(void *opaque)
@@ -905,23 +931,25 @@ static void cpu_ppc_decr_cb(void *opaque)
     cpu_ppc_decr_excp(cpu);
 }
 
-static inline void _cpu_ppc_store_hdecr(PowerPCCPU *cpu, uint32_t hdecr,
-                                        uint32_t value)
+static inline void _cpu_ppc_store_hdecr(PowerPCCPU *cpu, target_ulong hdecr,
+                                        target_ulong value, int nr_bits)
 {
     ppc_tb_t *tb_env = cpu->env.tb_env;
 
     if (tb_env->hdecr_timer != NULL) {
         __cpu_ppc_store_decr(cpu, &tb_env->hdecr_next, tb_env->hdecr_timer,
                              tb_env->hdecr_timer->cb, &cpu_ppc_hdecr_lower,
-                             hdecr, value);
+                             hdecr, value, nr_bits);
     }
 }
 
-void cpu_ppc_store_hdecr (CPUPPCState *env, uint32_t value)
+void cpu_ppc_store_hdecr (CPUPPCState *env, target_ulong value)
 {
     PowerPCCPU *cpu = ppc_env_get_cpu(env);
+    PowerPCCPUClass *pcc = POWERPC_CPU_GET_CLASS(cpu);
+    int nr_bits = (pcc->hdecr_bits > 32) ? pcc->hdecr_bits : 32;
 
-    _cpu_ppc_store_hdecr(cpu, cpu_ppc_load_hdecr(env), value);
+    _cpu_ppc_store_hdecr(cpu, cpu_ppc_load_hdecr(env), value, nr_bits);
 }
 
 static void cpu_ppc_hdecr_cb(void *opaque)
@@ -951,8 +979,8 @@ static void cpu_ppc_set_tb_clk (void *opaque, uint32_t freq)
      * if a decrementer exception is pending when it enables msr_ee at startup,
      * it's not ready to handle it...
      */
-    _cpu_ppc_store_decr(cpu, 0xFFFFFFFF, 0xFFFFFFFF);
-    _cpu_ppc_store_hdecr(cpu, 0xFFFFFFFF, 0xFFFFFFFF);
+    _cpu_ppc_store_decr(cpu, 0xFFFFFFFF, 0xFFFFFFFF, 32);
+    _cpu_ppc_store_hdecr(cpu, 0xFFFFFFFF, 0xFFFFFFFF, 32);
     cpu_ppc_store_purr(cpu, 0x0000000000000000ULL);
 }
 
diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
index acf62a2b9f..966bc74e68 100644
--- a/hw/ppc/spapr.c
+++ b/hw/ppc/spapr.c
@@ -557,6 +557,14 @@ static void spapr_populate_cpu_dt(CPUState *cs, void *fdt, int offset,
                           pcc->radix_page_info->count *
                           sizeof(radix_AP_encodings[0]))));
     }
+
+    /*
+     * We set this property to let the guest know that it can use the large
+     * decrementer and its width in bits.
+     */
+    if (env->large_decr_bits)
+        _FDT((fdt_setprop_u32(fdt, offset, "ibm,dec-bits",
+                              env->large_decr_bits)));
 }
 
 static void spapr_populate_cpus_dt_node(void *fdt, sPAPRMachineState *spapr)
diff --git a/hw/ppc/spapr_caps.c b/hw/ppc/spapr_caps.c
index 1545a02729..44542fdbb2 100644
--- a/hw/ppc/spapr_caps.c
+++ b/hw/ppc/spapr_caps.c
@@ -421,8 +421,43 @@ static void cap_nested_kvm_hv_apply(sPAPRMachineState *spapr,
 static void cap_large_decr_apply(sPAPRMachineState *spapr,
                                  uint8_t val, Error **errp)
 {
-    if (val)
+    PowerPCCPU *cpu = POWERPC_CPU(first_cpu);
+    PowerPCCPUClass *pcc = POWERPC_CPU_GET_CLASS(cpu);
+
+    if (!val)
+        return; /* Disabled by default */
+
+    if (tcg_enabled()) {
+        if (!ppc_check_compat(cpu, CPU_POWERPC_LOGICAL_3_00, 0,
+                              spapr->max_compat_pvr)) {
+            error_setg(errp,
+                "Large decrementer only supported on POWER9, try -cpu POWER9");
+            return;
+        }
+        if ((val < 32) || (val > pcc->hdecr_bits)) {
+            error_setg(errp,
+                "Large decrementer size unsupported, try -cap-large-decr=%d",
+                pcc->hdecr_bits);
+            return;
+        }
+    } else {
         error_setg(errp, "No large decrementer support, try cap-large-decr=0");
+    }
+}
+
+static void cap_large_decr_cpu_apply(sPAPRMachineState *spapr,
+                                     PowerPCCPU *cpu,
+                                     uint8_t val, Error **errp)
+{
+    CPUPPCState *env = &cpu->env;
+    target_ulong lpcr = env->spr[SPR_LPCR];
+
+    if (val)
+        lpcr |= LPCR_LD;
+    else
+        lpcr &= ~LPCR_LD;
+    ppc_store_lpcr(cpu, lpcr);
+    env->large_decr_bits = val;
 }
 
 sPAPRCapabilityInfo capability_table[SPAPR_CAP_NUM] = {
@@ -511,6 +546,7 @@ sPAPRCapabilityInfo capability_table[SPAPR_CAP_NUM] = {
         .set = spapr_cap_set_uint8,
         .type = "int",
         .apply = cap_large_decr_apply,
+        .cpu_apply = cap_large_decr_cpu_apply,
     },
 };
 
diff --git a/target/ppc/cpu-qom.h b/target/ppc/cpu-qom.h
index ae51fe754e..cced705e30 100644
--- a/target/ppc/cpu-qom.h
+++ b/target/ppc/cpu-qom.h
@@ -190,6 +190,7 @@ typedef struct PowerPCCPUClass {
 #endif
     const PPCHash64Options *hash64_opts;
     struct ppc_radix_page_info *radix_page_info;
+    uint32_t hdecr_bits;
     void (*init_proc)(CPUPPCState *env);
     int  (*check_pow)(CPUPPCState *env);
     int (*handle_mmu_fault)(PowerPCCPU *cpu, vaddr eaddr, int rwx, int mmu_idx);
diff --git a/target/ppc/cpu.h b/target/ppc/cpu.h
index 26604ddf98..8da333e9da 100644
--- a/target/ppc/cpu.h
+++ b/target/ppc/cpu.h
@@ -1171,6 +1171,9 @@ struct CPUPPCState {
     uint32_t tm_vscr;
     uint64_t tm_dscr;
     uint64_t tm_tar;
+
+    /* Large Decrementer */
+    int large_decr_bits;
 };
 
 #define SET_FIT_PERIOD(a_, b_, c_, d_)          \
@@ -1321,10 +1324,10 @@ uint32_t cpu_ppc_load_atbu (CPUPPCState *env);
 void cpu_ppc_store_atbl (CPUPPCState *env, uint32_t value);
 void cpu_ppc_store_atbu (CPUPPCState *env, uint32_t value);
 bool ppc_decr_clear_on_delivery(CPUPPCState *env);
-uint32_t cpu_ppc_load_decr (CPUPPCState *env);
-void cpu_ppc_store_decr (CPUPPCState *env, uint32_t value);
-uint32_t cpu_ppc_load_hdecr (CPUPPCState *env);
-void cpu_ppc_store_hdecr (CPUPPCState *env, uint32_t value);
+target_ulong cpu_ppc_load_decr (CPUPPCState *env);
+void cpu_ppc_store_decr (CPUPPCState *env, target_ulong value);
+target_ulong cpu_ppc_load_hdecr (CPUPPCState *env);
+void cpu_ppc_store_hdecr (CPUPPCState *env, target_ulong value);
 uint64_t cpu_ppc_load_purr (CPUPPCState *env);
 uint32_t cpu_ppc601_load_rtcl (CPUPPCState *env);
 uint32_t cpu_ppc601_load_rtcu (CPUPPCState *env);
diff --git a/target/ppc/mmu-hash64.c b/target/ppc/mmu-hash64.c
index c431303eff..a2b1ec5040 100644
--- a/target/ppc/mmu-hash64.c
+++ b/target/ppc/mmu-hash64.c
@@ -1109,7 +1109,7 @@ void ppc_store_lpcr(PowerPCCPU *cpu, target_ulong val)
     case POWERPC_MMU_3_00: /* P9 */
         lpcr = val & (LPCR_VPM1 | LPCR_ISL | LPCR_KBV | LPCR_DPFD |
                       (LPCR_PECE_U_MASK & LPCR_HVEE) | LPCR_ILE | LPCR_AIL |
-                      LPCR_UPRT | LPCR_EVIRT | LPCR_ONL | LPCR_HR |
+                      LPCR_UPRT | LPCR_EVIRT | LPCR_ONL | LPCR_HR | LPCR_LD |
                       (LPCR_PECE_L_MASK & (LPCR_PDEE | LPCR_HDEE | LPCR_EEE |
                       LPCR_DEE | LPCR_OEE)) | LPCR_MER | LPCR_GTSE | LPCR_TC |
                       LPCR_HEIC | LPCR_LPES0 | LPCR_HVICE | LPCR_HDICE);
diff --git a/target/ppc/translate.c b/target/ppc/translate.c
index 819221f246..b156be4d98 100644
--- a/target/ppc/translate.c
+++ b/target/ppc/translate.c
@@ -7417,7 +7417,7 @@ void ppc_cpu_dump_state(CPUState *cs, FILE *f, fprintf_function cpu_fprintf,
 #if !defined(NO_TIMER_DUMP)
     cpu_fprintf(f, "TB %08" PRIu32 " %08" PRIu64
 #if !defined(CONFIG_USER_ONLY)
-                " DECR %08" PRIu32
+                " DECR " TARGET_FMT_lu
 #endif
                 "\n",
                 cpu_ppc_load_tbu(env), cpu_ppc_load_tbl(env)
diff --git a/target/ppc/translate_init.inc.c b/target/ppc/translate_init.inc.c
index 58542c0fe0..4e0bf1f47a 100644
--- a/target/ppc/translate_init.inc.c
+++ b/target/ppc/translate_init.inc.c
@@ -8926,6 +8926,7 @@ POWERPC_FAMILY(POWER9)(ObjectClass *oc, void *data)
     /* segment page size remain the same */
     pcc->hash64_opts = &ppc_hash64_opts_POWER7;
     pcc->radix_page_info = &POWER9_radix_page_info;
+    pcc->hdecr_bits = 56;
 #endif
     pcc->excp_model = POWERPC_EXCP_POWER9;
     pcc->bus_model = PPC_FLAGS_INPUT_POWER9;
-- 
2.13.6