[PATCH 1/2] target/riscv: disable *stimecmp interrupts without *envcfg.STCE

["Radim Krčmář" <rkrcmar@ventanamicro.com>]

The specification states that menvcfg.STCE=0 prevents both *stimecmp
CSRs from having an effect on the pending interrupts.
henvcfg.STCE=0 disables only vstimecmp.

Make sure that when *envcfg.STCE is not set:
* writing the *stimecmp CSRs doesn't modify the *ip CSRs,
* and that the interrupt timer is disarmed.

Call the *stimecmp CSR update functions when *envcfg.STCE is toggled,
because the *ip CSRs need to immediately reflect the new behavior.

Fixes: 43888c2f1823 ("target/riscv: Add stimecmp support")
Signed-off-by: Radim Krčmář <rkrcmar@ventanamicro.com>
---
 target/riscv/csr.c         | 12 ++++++++++++
 target/riscv/time_helper.c | 10 ++++++++++
 2 files changed, 22 insertions(+)

diff --git a/target/riscv/csr.c b/target/riscv/csr.c
index fb149721691d..43eae9bcf153 100644
--- a/target/riscv/csr.c
+++ b/target/riscv/csr.c
@@ -3181,6 +3181,7 @@ static RISCVException write_menvcfg(CPURISCVState *env, int csrno,
     const RISCVCPUConfig *cfg = riscv_cpu_cfg(env);
     uint64_t mask = MENVCFG_FIOM | MENVCFG_CBIE | MENVCFG_CBCFE |
                     MENVCFG_CBZE | MENVCFG_CDE;
+    typeof(env->menvcfg) old = env->menvcfg;
 
     if (riscv_cpu_mxl(env) == MXL_RV64) {
         mask |= (cfg->ext_svpbmt ? MENVCFG_PBMTE : 0) |
@@ -3208,6 +3209,11 @@ static RISCVException write_menvcfg(CPURISCVState *env, int csrno,
         }
     }
     env->menvcfg = (env->menvcfg & ~mask) | (val & mask);
+
+    if ((old ^ env->menvcfg) & MENVCFG_STCE) {
+        riscv_timer_write_timecmp(env, env->stimer, env->stimecmp, 0, MIP_STIP);
+    }
+
     return write_henvcfg(env, CSR_HENVCFG, env->henvcfg, ra);
 }
 
@@ -3314,6 +3320,7 @@ static RISCVException write_henvcfg(CPURISCVState *env, int csrno,
                                     target_ulong val, uintptr_t ra)
 {
     uint64_t mask = HENVCFG_FIOM | HENVCFG_CBIE | HENVCFG_CBCFE | HENVCFG_CBZE;
+    typeof(env->henvcfg) old = env->henvcfg;
     RISCVException ret;
 
     ret = smstateen_acc_ok(env, 0, SMSTATEEN0_HSENVCFG);
@@ -3347,6 +3354,11 @@ static RISCVException write_henvcfg(CPURISCVState *env, int csrno,
         env->vsstatus &= ~MSTATUS_SDT;
     }
 
+    if ((old ^ env->henvcfg) & HENVCFG_STCE) {
+        riscv_timer_write_timecmp(env, env->vstimer, env->vstimecmp,
+                                  env->htimedelta, MIP_VSTIP);
+    }
+
     return RISCV_EXCP_NONE;
 }
 
diff --git a/target/riscv/time_helper.c b/target/riscv/time_helper.c
index bc0d9a0c4c35..8198a2d8d92d 100644
--- a/target/riscv/time_helper.c
+++ b/target/riscv/time_helper.c
@@ -49,6 +49,16 @@ void riscv_timer_write_timecmp(CPURISCVState *env, QEMUTimer *timer,
     uint32_t timebase_freq = mtimer->timebase_freq;
     uint64_t rtc_r = env->rdtime_fn(env->rdtime_fn_arg) + delta;
 
+    /*
+     * *envcfg.STCE disables *stimecmp interrupts, but still allows higher
+     * privileges to write the *stimecmp CSRs.
+     */
+    if (!get_field(env->menvcfg, MENVCFG_STCE) ||
+        (timer_irq == MIP_VSTIP && !get_field(env->henvcfg, HENVCFG_STCE))) {
+        timer_del(timer);
+        return;
+    }
+
     if (timecmp <= rtc_r) {
         /*
          * If we're setting an stimecmp value in the "past",
-- 
2.49.0