[PATCH] include virtualization mode as part of priv

[Yanfeng <yfliu2008@qq.com>]

When debugging hypervisor extension based programs, it is convenient to see the
current virtualization mode from GDB debugger.

This patch shares the virtualization mode as part of the existing "priv" virtual
register, or more specifically via bit(8).


>From 0d82561b11e1c2835f14ba5460cfff52f0087530 Mon Sep 17 00:00:00 2001
From: Yanfeng Liu <yfliu2008@qq.com>
Date: Mon, 18 Nov 2024 08:03:15 +0800
Subject: [PATCH] riscv/gdb: share virt mode via priv register

This shares virtualization mode together with privilege mode
via the `priv` virtual register over the debug interface.

Check logs with gdb-multiarch 12.1:

```
(gdb) info registers priv
priv           0x101	prv:1 [Supervisor]
(gdb) set $priv = 1
(gdb) info registers priv
priv           0x1	prv:1 [Supervisor]
(gdb) set $priv = 0x101
(gdb) info registers priv
priv           0x101	prv:1 [Supervisor]
(gdb)
```

Signed-off-by: Yanfeng Liu <yfliu2008@qq.com>
---
 target/riscv/cpu_bits.h |  4 ++++
 target/riscv/gdbstub.c  | 15 +++++++++++++--
 2 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/target/riscv/cpu_bits.h b/target/riscv/cpu_bits.h
index 385a2c67c2..cc6dece51a 100644
--- a/target/riscv/cpu_bits.h
+++ b/target/riscv/cpu_bits.h
@@ -623,6 +623,10 @@ typedef enum {
 #define PRV_RESERVED 2
 #define PRV_M 3
 
+/* Share virtualization mode as part of priv register */
+#define PRV_V                (1 << 8)
+
+
 /* RV32 satp CSR field masks */
 #define SATP32_MODE         0x80000000
 #define SATP32_ASID         0x7fc00000
diff --git a/target/riscv/gdbstub.c b/target/riscv/gdbstub.c
index c07df972f1..d9e6ad969a 100644
--- a/target/riscv/gdbstub.c
+++ b/target/riscv/gdbstub.c
@@ -212,8 +212,14 @@ static int riscv_gdb_get_virtual(CPUState *cs, GByteArray
*buf, int n)
 #else
         RISCVCPU *cpu = RISCV_CPU(cs);
         CPURISCVState *env = &cpu->env;
+        target_ulong ret = env->priv;
 
-        return gdb_get_regl(buf, env->priv);
+        /* include virtualization mode */
+
+        if (env->virt_enabled) {
+            ret |= PRV_V;
+        }
+        return gdb_get_regl(buf, ret);
 #endif
     }
     return 0;
@@ -225,11 +231,16 @@ static int riscv_gdb_set_virtual(CPUState *cs, uint8_t
*mem_buf, int n)
 #ifndef CONFIG_USER_ONLY
         RISCVCPU *cpu = RISCV_CPU(cs);
         CPURISCVState *env = &cpu->env;
+        target_ulong val = ldtul_p(mem_buf);
 
-        env->priv = ldtul_p(mem_buf) & 0x3;
+        env->priv = val & 0x3;
         if (env->priv == PRV_RESERVED) {
             env->priv = PRV_S;
         }
+
+        /* Update virtualization mode */
+
+        env->virt_enabled = (env->priv != PRV_M && (val & PRV_V) != 0);
 #endif
         return sizeof(target_ulong);
     }
-- 
2.34.1