RISC-V: Allow setting and clearing multiple irqs

Change the API of riscv_set_local_interrupt to take a
write mask and value to allow setting and clearing of
multiple local interrupts atomically in a single call.
Rename the new function to riscv_cpu_update_mip.

Signed-off-by: Michael Clark <mjc@sifive.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Palmer Dabbelt <palmer@sifive.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
Signed-off-by: Palmer Dabbelt <palmer@sifive.com>

hw/riscv/sifive_clint.c

@@ -47,12 +47,12 @@ static void sifive_clint_write_timecmp(RISCVCPU *cpu, uint64_t value)
     if (cpu->env.timecmp <= rtc_r) {
         /* if we're setting an MTIMECMP value in the "past",
            immediately raise the timer interrupt */
-        riscv_set_local_interrupt(cpu, MIP_MTIP, 1);
+        riscv_cpu_update_mip(cpu, MIP_MTIP, BOOL_TO_MASK(1));
         return;
     }
 
     /* otherwise, set up the future timer interrupt */
-    riscv_set_local_interrupt(cpu, MIP_MTIP, 0);
+    riscv_cpu_update_mip(cpu, MIP_MTIP, BOOL_TO_MASK(0));
     diff = cpu->env.timecmp - rtc_r;
     /* back to ns (note args switched in muldiv64) */
     next = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) +
@@ -67,7 +67,7 @@ static void sifive_clint_write_timecmp(RISCVCPU *cpu, uint64_t value)
 static void sifive_clint_timer_cb(void *opaque)
 {
     RISCVCPU *cpu = opaque;
-    riscv_set_local_interrupt(cpu, MIP_MTIP, 1);
+    riscv_cpu_update_mip(cpu, MIP_MTIP, BOOL_TO_MASK(1));
 }
 
 /* CPU wants to read rtc or timecmp register */
@@ -132,7 +132,7 @@ static void sifive_clint_write(void *opaque, hwaddr addr, uint64_t value,
         if (!env) {
             error_report("clint: invalid timecmp hartid: %zu", hartid);
         } else if ((addr & 0x3) == 0) {
-            riscv_set_local_interrupt(RISCV_CPU(cpu), MIP_MSIP, value != 0);
+            riscv_cpu_update_mip(RISCV_CPU(cpu), MIP_MSIP, BOOL_TO_MASK(value));
         } else {
             error_report("clint: invalid sip write: %08x", (uint32_t)addr);
         }

hw/riscv/sifive_plic.c

@@ -142,10 +142,10 @@ static void sifive_plic_update(SiFivePLICState *plic)
         int level = sifive_plic_irqs_pending(plic, addrid);
         switch (mode) {
         case PLICMode_M:
-            riscv_set_local_interrupt(RISCV_CPU(cpu), MIP_MEIP, level);
+            riscv_cpu_update_mip(RISCV_CPU(cpu), MIP_MEIP, BOOL_TO_MASK(level));
             break;
         case PLICMode_S:
-            riscv_set_local_interrupt(RISCV_CPU(cpu), MIP_SEIP, level);
+            riscv_cpu_update_mip(RISCV_CPU(cpu), MIP_SEIP, BOOL_TO_MASK(level));
             break;
         default:
             break;

target/riscv/cpu.h

@@ -126,13 +126,18 @@ struct CPURISCVState {
 
     target_ulong mhartid;
     target_ulong mstatus;
+
     /*
      * CAUTION! Unlike the rest of this struct, mip is accessed asynchonously
-     * by I/O threads and other vCPUs, so hold the iothread mutex before
+     * by I/O threads. It should be read with atomic_read. It should be updated
-     * operating on it.  CPU_INTERRUPT_HARD should be in effect iff this is
+     * using riscv_cpu_update_mip with the iothread mutex held. The iothread
-     * non-zero.  Use riscv_cpu_set_local_interrupt.
+     * mutex must be held because mip must be consistent with the CPU inturrept
+     * state. riscv_cpu_update_mip calls cpu_interrupt or cpu_reset_interrupt
+     * wuth the invariant that CPU_INTERRUPT_HARD is set iff mip is non-zero.
+     * mip is 32-bits to allow atomic_read on 32-bit hosts.
      */
-    uint32_t mip;        /* allow atomic_read for >= 32-bit hosts */
+    uint32_t mip;
+
     target_ulong mie;
     target_ulong mideleg;
 
@@ -247,7 +252,6 @@ void  riscv_cpu_do_unaligned_access(CPUState *cs, vaddr addr,
                                     uintptr_t retaddr);
 int riscv_cpu_handle_mmu_fault(CPUState *cpu, vaddr address, int size,
                               int rw, int mmu_idx);
-
 char *riscv_isa_string(RISCVCPU *cpu);
 void riscv_cpu_list(FILE *f, fprintf_function cpu_fprintf);
 
@@ -255,6 +259,10 @@ void riscv_cpu_list(FILE *f, fprintf_function cpu_fprintf);
 #define cpu_list riscv_cpu_list
 #define cpu_mmu_index riscv_cpu_mmu_index
 
+#ifndef CONFIG_USER_ONLY
+uint32_t riscv_cpu_update_mip(RISCVCPU *cpu, uint32_t mask, uint32_t value);
+#define BOOL_TO_MASK(x) (-!!(x)) /* helper for riscv_cpu_update_mip value */
+#endif
 void riscv_set_mode(CPURISCVState *env, target_ulong newpriv);
 
 void riscv_translate_init(void);
@@ -285,10 +293,6 @@ void csr_write_helper(CPURISCVState *env, target_ulong val_to_write,
         target_ulong csrno);
 target_ulong csr_read_helper(CPURISCVState *env, target_ulong csrno);
 
-#ifndef CONFIG_USER_ONLY
-void riscv_set_local_interrupt(RISCVCPU *cpu, target_ulong mask, int value);
-#endif
-
 #include "exec/cpu-all.h"
 
 #endif /* RISCV_CPU_H */

target/riscv/op_helper.c

@@ -171,10 +171,8 @@ void csr_write_helper(CPURISCVState *env, target_ulong val_to_write,
          */
         qemu_mutex_lock_iothread();
         RISCVCPU *cpu = riscv_env_get_cpu(env);
-        riscv_set_local_interrupt(cpu, MIP_SSIP,
+        riscv_cpu_update_mip(cpu, MIP_SSIP | MIP_STIP,
-                                  (val_to_write & MIP_SSIP) != 0);
+                                  (val_to_write & (MIP_SSIP | MIP_STIP)));
-        riscv_set_local_interrupt(cpu, MIP_STIP,
-                                  (val_to_write & MIP_STIP) != 0);
         /*
          * csrs, csrc on mip.SEIP is not decomposable into separate read and
          * write steps, so a different implementation is needed
@@ -657,16 +655,24 @@ target_ulong helper_csrrc(CPURISCVState *env, target_ulong src,
 #ifndef CONFIG_USER_ONLY
 
 /* iothread_mutex must be held */
-void riscv_set_local_interrupt(RISCVCPU *cpu, target_ulong mask, int value)
+uint32_t riscv_cpu_update_mip(RISCVCPU *cpu, uint32_t mask, uint32_t value)
 {
-    target_ulong old_mip = cpu->env.mip;
+    CPURISCVState *env = &cpu->env;
-    cpu->env.mip = (old_mip & ~mask) | (value ? mask : 0);
+    uint32_t old, new, cmp = atomic_read(&env->mip);
 
-    if (cpu->env.mip && !old_mip) {
+    do {
+        old = cmp;
+        new = (old & ~mask) | (value & mask);
+        cmp = atomic_cmpxchg(&env->mip, old, new);
+    } while (old != cmp);
+
+    if (new && !old) {
         cpu_interrupt(CPU(cpu), CPU_INTERRUPT_HARD);
-    } else if (!cpu->env.mip && old_mip) {
+    } else if (!new && old) {
         cpu_reset_interrupt(CPU(cpu), CPU_INTERRUPT_HARD);
     }
+
+    return old;
 }
 
 void riscv_set_mode(CPURISCVState *env, target_ulong newpriv)