[PATCH v2 01/18] target/riscv: skip features setup for KVM CPUs

[Daniel Henrique Barboza]

As it is today it's not possible to use '-cpu host' if the RISC-V host
has RVH enabled. This is the resulting error:

$ sudo ./qemu/build/qemu-system-riscv64 \
    -machine virt,accel=kvm -m 2G -smp 1 \
    -nographic -snapshot -kernel ./guest_imgs/Image  \
    -initrd ./guest_imgs/rootfs_kvm_riscv64.img \
    -append "earlycon=sbi root=/dev/ram rw" \
    -cpu host
qemu-system-riscv64: H extension requires priv spec 1.12.0

This happens because we're checking for priv spec for all CPUs, and
since we're not setting  env->priv_ver for the 'host' CPU, it's being
default to zero (i.e. PRIV_SPEC_1_10_0).

In reality env->priv_ver does not make sense when running with the KVM
'host' CPU. It's used to gate certain CSRs/extensions during translation
to make them unavailable if the hart declares an older spec version. It
doesn't have any other use. E.g. OpenSBI version 1.2 retrieves the spec
checking if the CSR_MCOUNTEREN, CSR_MCOUNTINHIBIT and CSR_MENVCFG CSRs
are available [1].

'priv_ver' is just one example. We're doing a lot of feature validation
and setup during riscv_cpu_realize() that it doesn't apply KVM CPUs.
Validating the feature set for those CPUs is a KVM problem that should
be handled in KVM specific code.

The new riscv_cpu_realize_features() helper contains all validation
logic that are not applicable to KVM CPUs. riscv_cpu_realize() verifies
if we're dealing with a KVM CPU and, if not, execute the new helper to
proceed with the usual realize() logic for all other CPUs.

[1] lib/sbi/sbi_hart.c, hart_detect_features()

Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
---
 target/riscv/cpu.c | 43 +++++++++++++++++++++++++++++++++----------
 1 file changed, 33 insertions(+), 10 deletions(-)

diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
index 881bddf393..e904018644 100644
--- a/target/riscv/cpu.c
+++ b/target/riscv/cpu.c
@@ -331,6 +331,15 @@ static void set_satp_mode_default_map(RISCVCPU *cpu)
 }
 #endif
 
+static bool riscv_running_kvm(void)
+{
+#ifndef CONFIG_USER_ONLY
+    return kvm_enabled();
+#else
+    return false;
+#endif
+}
+
 static void riscv_any_cpu_init(Object *obj)
 {
     RISCVCPU *cpu = RISCV_CPU(obj);
@@ -1304,20 +1313,12 @@ static void riscv_cpu_validate_misa_priv(CPURISCVState 
*env, Error **errp)
     }
 }
 
-static void riscv_cpu_realize(DeviceState *dev, Error **errp)
+static void riscv_cpu_realize_features(DeviceState *dev, Error **errp)
 {
-    CPUState *cs = CPU(dev);
     RISCVCPU *cpu = RISCV_CPU(dev);
     CPURISCVState *env = &cpu->env;
-    RISCVCPUClass *mcc = RISCV_CPU_GET_CLASS(dev);
     Error *local_err = NULL;
 
-    cpu_exec_realizefn(cs, &local_err);
-    if (local_err != NULL) {
-        error_propagate(errp, local_err);
-        return;
-    }
-
     riscv_cpu_validate_misa_mxl(cpu, &local_err);
     if (local_err != NULL) {
         error_propagate(errp, local_err);
@@ -1352,7 +1353,7 @@ static void riscv_cpu_realize(DeviceState *dev, Error 
**errp)
     }
 
 #ifndef CONFIG_USER_ONLY
-    cs->tcg_cflags |= CF_PCREL;
+    CPU(dev)->tcg_cflags |= CF_PCREL;
 
     if (cpu->cfg.ext_sstc) {
         riscv_timer_init(cpu);
@@ -1365,6 +1366,28 @@ static void riscv_cpu_realize(DeviceState *dev, Error 
**errp)
         }
      }
 #endif
+}
+
+static void riscv_cpu_realize(DeviceState *dev, Error **errp)
+{
+    CPUState *cs = CPU(dev);
+    RISCVCPU *cpu = RISCV_CPU(dev);
+    RISCVCPUClass *mcc = RISCV_CPU_GET_CLASS(dev);
+    Error *local_err = NULL;
+
+    cpu_exec_realizefn(cs, &local_err);
+    if (local_err != NULL) {
+        error_propagate(errp, local_err);
+        return;
+    }
+
+    if (!riscv_running_kvm()) {
+        riscv_cpu_realize_features(dev, &local_err);
+        if (local_err != NULL) {
+            error_propagate(errp, local_err);
+            return;
+        }
+    }
 
     riscv_cpu_finalize_features(cpu, &local_err);
     if (local_err != NULL) {
-- 
2.40.1