target/riscv: add zihpm extension flag for TCG

zihpm is the Hardware Performance Counters extension described in
chapter 12 of the unprivileged spec. It describes support for 29
unprivileged performance counters, hpmcounter3-hpmcounter31.

As with zicntr, QEMU already implements zihpm before it was even an
extension. zihpm is also part of the RVA22 profile, so add it to QEMU
to complement the future profile implementation. Default it to 'true'
for all existing CPUs since it was always present in the code.

As for disabling it, there is already code in place in
target/riscv/csr.c in all predicates for these counters (ctr() and
mctr()) that disables them if cpu->cfg.pmu_num is zero. Thus, setting
cpu->cfg.pmu_num to zero if 'zihpm=false' is enough to disable the
extension.

Set cpu->pmu_avail_ctrs mask to zero as well since this is also checked
to verify if the counters exist.

Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-ID: <20231023153927.435083-4-dbarboza@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

1 files changed, 13 insertions, 0 deletions

diff --git a/target/riscv/tcg/tcg-cpu.c b/target/riscv/tcg/tcg-cpu.c
index a1e4ed2..093bda2 100644
--- a/target/riscv/tcg/tcg-cpu.c
+++ b/target/riscv/tcg/tcg-cpu.c
@@ -549,6 +549,19 @@ void riscv_cpu_validate_set_extensions(RISCVCPU *cpu, Error **errp)
         cpu->cfg.ext_zicntr = false;
     }
 
+    if (cpu->cfg.ext_zihpm && !cpu->cfg.ext_zicsr) {
+        if (cpu_cfg_ext_is_user_set(CPU_CFG_OFFSET(ext_zihpm))) {
+            error_setg(errp, "zihpm requires zicsr");
+            return;
+        }
+        cpu->cfg.ext_zihpm = false;
+    }
+
+    if (!cpu->cfg.ext_zihpm) {
+        cpu->cfg.pmu_num = 0;
+        cpu->pmu_avail_ctrs = 0;
+    }
+
     /*
      * Disable isa extensions based on priv spec after we
      * validated and set everything we need.