[PATCH v2] riscv: Add RISCVCPUConfig.satp_mode to set sv48, sv57, etc.

[Alexandre Ghiti <alexghiti@rivosinc.com>]

RISC-V specifies multiple sizes for addressable memory and Linux probes for
the machine's support at startup via the satp CSR register (done in
csr.c:validate_vm).

As per the specification, sv64 must support sv57, which in turn must
support sv48...etc. So we can restrict machine support by simply setting the
"highest" supported mode in the satp_mode property. And the bare mode is
always supported.

You can set this new property as follows:
-cpu rv64,satp-mode=sv48 # Linux will boot using sv48 scheme
-cpu rv64,satp-mode=sv39 # Linux will boot using sv39 scheme

In addition, we now correctly set the device-tree entry 'mmu-type' using
this new satp_mode property.

Reviewed-by: Atish Patra <atishp@rivosinc.com>
Co-Developed-by: Ludovic Henry <ludovic@rivosinc.com>
Signed-off-by: Ludovic Henry <ludovic@rivosinc.com>
Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
---

v2:
- Use error_setg + return as suggested by Alistair
- Add RB from Atish
- Fixed checkpatch issues missed in v1
- Replaced Ludovic email address with the rivos one

 hw/riscv/virt.c    | 15 ++++++---------
 target/riscv/cpu.c | 45 +++++++++++++++++++++++++++++++++++++++++++++
 target/riscv/cpu.h |  3 +++
 target/riscv/csr.c |  8 ++++++--
 4 files changed, 60 insertions(+), 11 deletions(-)

diff --git a/hw/riscv/virt.c b/hw/riscv/virt.c
index a5bc7353b4..77484b5cae 100644
--- a/hw/riscv/virt.c
+++ b/hw/riscv/virt.c
@@ -228,7 +228,7 @@ static void create_fdt_socket_cpus(RISCVVirtState *s, int socket,
     int cpu;
     uint32_t cpu_phandle;
     MachineState *mc = MACHINE(s);
-    char *name, *cpu_name, *core_name, *intc_name;
+    char *name, *cpu_name, *core_name, *intc_name, *sv_name;
 
     for (cpu = s->soc[socket].num_harts - 1; cpu >= 0; cpu--) {
         cpu_phandle = (*phandle)++;
@@ -236,14 +236,11 @@ static void create_fdt_socket_cpus(RISCVVirtState *s, int socket,
         cpu_name = g_strdup_printf("/cpus/cpu@%d",
             s->soc[socket].hartid_base + cpu);
         qemu_fdt_add_subnode(mc->fdt, cpu_name);
-        if (riscv_feature(&s->soc[socket].harts[cpu].env,
-                          RISCV_FEATURE_MMU)) {
-            qemu_fdt_setprop_string(mc->fdt, cpu_name, "mmu-type",
-                                    (is_32_bit) ? "riscv,sv32" : "riscv,sv48");
-        } else {
-            qemu_fdt_setprop_string(mc->fdt, cpu_name, "mmu-type",
-                                    "riscv,none");
-        }
+
+        sv_name = g_strdup_printf("riscv,%s",
+                                  s->soc[socket].harts[cpu].cfg.satp_mode_str);
+        qemu_fdt_setprop_string(mc->fdt, cpu_name, "mmu-type", sv_name);
+
         name = riscv_isa_string(&s->soc[socket].harts[cpu]);
         qemu_fdt_setprop_string(mc->fdt, cpu_name, "riscv,isa", name);
         g_free(name);
diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
index d14e95c9dc..c86dc5058d 100644
--- a/target/riscv/cpu.c
+++ b/target/riscv/cpu.c
@@ -907,6 +907,48 @@ static void riscv_cpu_realize(DeviceState *dev, Error **errp)
      }
 #endif
 
+    /*
+     * Either a cpu sets its supported satp_mode in XXX_cpu_init
+     * or the user sets this value using satp_mode property.
+     */
+    bool rv32 = riscv_cpu_mxl(&cpu->env) == MXL_RV32;
+    if (cpu->cfg.satp_mode_str) {
+        if (!g_strcmp0(cpu->cfg.satp_mode_str, "none"))
+            cpu->cfg.satp_mode = VM_1_10_MBARE;
+        else if (!g_strcmp0(cpu->cfg.satp_mode_str, "sv32") && rv32)
+            cpu->cfg.satp_mode = VM_1_10_SV32;
+        else if (!g_strcmp0(cpu->cfg.satp_mode_str, "sv39") && !rv32)
+            cpu->cfg.satp_mode = VM_1_10_SV39;
+        else if (!g_strcmp0(cpu->cfg.satp_mode_str, "sv48") && !rv32)
+            cpu->cfg.satp_mode = VM_1_10_SV48;
+        else if (!g_strcmp0(cpu->cfg.satp_mode_str, "sv57") && !rv32)
+            cpu->cfg.satp_mode = VM_1_10_SV57;
+        else if (!g_strcmp0(cpu->cfg.satp_mode_str, "sv64") && !rv32)
+            cpu->cfg.satp_mode = VM_1_10_SV64;
+        else {
+            error_setg(errp, "Unknown option for satp_mode: %s",
+                       cpu->cfg.satp_mode_str);
+            return;
+        }
+    } else {
+        /*
+         * If unset by both the user and the cpu, we fallback to sv32 for 32-bit
+         * or sv57 for 64-bit when a MMU is present, and bare otherwise.
+         */
+        if (riscv_feature(&cpu->env, RISCV_FEATURE_MMU)) {
+            if (rv32) {
+                cpu->cfg.satp_mode_str = g_strdup("sv32");
+                cpu->cfg.satp_mode = VM_1_10_SV32;
+            } else {
+                cpu->cfg.satp_mode_str = g_strdup("sv57");
+                cpu->cfg.satp_mode = VM_1_10_SV57;
+            }
+        } else {
+            cpu->cfg.satp_mode_str = g_strdup("none");
+            cpu->cfg.satp_mode = VM_1_10_MBARE;
+        }
+    }
+
     riscv_cpu_register_gdb_regs_for_features(cs);
 
     qemu_init_vcpu(cs);
@@ -1094,6 +1136,9 @@ static Property riscv_cpu_properties[] = {
 
     DEFINE_PROP_BOOL("rvv_ta_all_1s", RISCVCPU, cfg.rvv_ta_all_1s, false),
     DEFINE_PROP_BOOL("rvv_ma_all_1s", RISCVCPU, cfg.rvv_ma_all_1s, false),
+
+    DEFINE_PROP_STRING("satp-mode", RISCVCPU, cfg.satp_mode_str),
+
     DEFINE_PROP_END_OF_LIST(),
 };
 
diff --git a/target/riscv/cpu.h b/target/riscv/cpu.h
index 3a9e25053f..a6c229470b 100644
--- a/target/riscv/cpu.h
+++ b/target/riscv/cpu.h
@@ -480,6 +480,9 @@ struct RISCVCPUConfig {
     bool debug;
 
     bool short_isa_string;
+
+    uint8_t satp_mode;
+    char *satp_mode_str;
 };
 
 typedef struct RISCVCPUConfig RISCVCPUConfig;
diff --git a/target/riscv/csr.c b/target/riscv/csr.c
index 5c9a7ee287..d2aab1627e 100644
--- a/target/riscv/csr.c
+++ b/target/riscv/csr.c
@@ -1109,10 +1109,14 @@ static RISCVException read_mstatus(CPURISCVState *env, int csrno,
 
 static int validate_vm(CPURISCVState *env, target_ulong vm)
 {
+    vm &= 0xf;
+
     if (riscv_cpu_mxl(env) == MXL_RV32) {
-        return valid_vm_1_10_32[vm & 0xf];
+        return valid_vm_1_10_32[vm] &&
+            (vm <= RISCV_CPU(env_cpu(env))->cfg.satp_mode);
     } else {
-        return valid_vm_1_10_64[vm & 0xf];
+        return valid_vm_1_10_64[vm] &&
+            (vm <= RISCV_CPU(env_cpu(env))->cfg.satp_mode);
     }
 }
 
-- 
2.37.2