target/riscv: Allow software access to MIP SEIP

The RISC-V specification states that:
  "Supervisor-level external interrupts are made pending based on the
  logical-OR of the software-writable SEIP bit and the signal from the
  external interrupt controller."

We currently only allow either the interrupt controller or software to
set the bit, which is incorrect.

This patch removes the miclaim mask when writing MIP to allow M-mode
software to inject interrupts, even with an interrupt controller.

We then also need to keep track of which source is setting MIP_SEIP. The
final value is a OR of both, so we add two bools and use that to keep
track of the current state. This way either source can change without
losing the correct value.

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/904
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20220317061817.3856850-3-alistair.francis@opensource.wdc.com>

3 files changed, 23 insertions, 3 deletions

diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
index 78fc7b2..cfdfe78 100644
--- a/target/riscv/cpu.c
+++ b/target/riscv/cpu.c
@@ -708,7 +708,6 @@ static void riscv_cpu_set_irq(void *opaque, int irq, int level)
         case IRQ_VS_TIMER:
         case IRQ_M_TIMER:
         case IRQ_U_EXT:
-        case IRQ_S_EXT:
         case IRQ_VS_EXT:
         case IRQ_M_EXT:
             if (kvm_enabled()) {
@@ -717,6 +716,15 @@ static void riscv_cpu_set_irq(void *opaque, int irq, int level)
                 riscv_cpu_update_mip(cpu, 1 << irq, BOOL_TO_MASK(level));
             }
              break;
+        case IRQ_S_EXT:
+            if (kvm_enabled()) {
+                kvm_riscv_set_irq(cpu, irq, level);
+            } else {
+                env->external_seip = level;
+                riscv_cpu_update_mip(cpu, 1 << irq,
+                                     BOOL_TO_MASK(level | env->software_seip));
+            }
+            break;
         default:
             g_assert_not_reached();
         }
diff --git a/target/riscv/cpu.h b/target/riscv/cpu.h
index e129c3d..b90ca82 100644
--- a/target/riscv/cpu.h
+++ b/target/riscv/cpu.h
@@ -177,6 +177,14 @@ struct CPUArchState {
     uint64_t mstatus;
 
     uint64_t mip;
+    /*
+     * MIP contains the software writable version of SEIP ORed with the
+     * external interrupt value. The MIP register is always up-to-date.
+     * To keep track of the current source, we also save booleans of the values
+     * here.
+     */
+    bool external_seip;
+    bool software_seip;
 
     uint64_t miclaim;
 
diff --git a/target/riscv/csr.c b/target/riscv/csr.c
index 8b6a1b9..a09126a 100644
--- a/target/riscv/csr.c
+++ b/target/riscv/csr.c
@@ -1498,10 +1498,14 @@ static RISCVException rmw_mip64(CPURISCVState *env, int csrno,
                                 uint64_t new_val, uint64_t wr_mask)
 {
     RISCVCPU *cpu = env_archcpu(env);
-    /* Allow software control of delegable interrupts not claimed by hardware */
-    uint64_t old_mip, mask = wr_mask & delegable_ints & ~env->miclaim;
+    uint64_t old_mip, mask = wr_mask & delegable_ints;
     uint32_t gin;
 
+    if (mask & MIP_SEIP) {
+        env->software_seip = new_val & MIP_SEIP;
+        new_val |= env->external_seip * MIP_SEIP;
+    }
+
     if (mask) {
         old_mip = riscv_cpu_update_mip(cpu, mask, (new_val & mask));
     } else {