[PATCH] target/riscv/kvm/kvm-cpu: Fixed the issue of resume after QEMU+KVM migration

[谢波]

This patch fixes two critical issues in QEMU with KVM:

1. Post-Migration Failure in User Mode: When QEMU with KVM is running in user 
mode, the guest may fail to function correctly after migration due to incorrect 
privilege state restoration.

2. Multi-Core Guest Inconsistency: After migration, only the first CPU (core 0) 
remains functional, while all other cores become unresponsive. This patch 
ensures all cores are properly set to runnable state after migration.

Changes include:
- Properly restoring guest privileged state during register synchronization.
- Correctly updating multi-core state after migration to ensure all cores are 
active.

Signed-off-by: Xie Bo <x...@ultrarisc.com>

---
 target/riscv/kvm/kvm-cpu.c | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

--- a/target/riscv/kvm/kvm-cpu.c
+++ b/target/riscv/kvm/kvm-cpu.c
@@ -576,6 +576,14 @@ static int kvm_riscv_get_regs_core(CPUState *cs)
     }
     env->pc = reg;

+    /* Restore guest privilege level after migration */
+    ret = kvm_get_one_reg(cs, RISCV_CORE_REG(env, mode), &reg);
+    if (ret) {
+        return ret;
+    }
+    if (reg != 3) {
+        env->priv = reg;
+    }

     for (i = 1; i < 32; i++) {
         uint64_t id = kvm_riscv_reg_id_ulong(env, KVM_REG_RISCV_CORE, i);
         ret = kvm_get_one_reg(cs, id, &reg);
@@ -601,6 +609,15 @@ static int kvm_riscv_put_regs_core(CPUState *cs)
         return ret;
     }

+    /* Save guest privilege level before migration */
+    reg = env->priv;
+    if (reg != 3) {
+        ret = kvm_set_one_reg(cs, RISCV_CORE_REG(env, mode), &reg);
+        if (ret) {
+            return ret;
+        }
+    }
+
     for (i = 1; i < 32; i++) {
         uint64_t id = kvm_riscv_reg_id_ulong(env, KVM_REG_RISCV_CORE, i);
         reg = env->gpr[i];
@@ -1289,6 +1306,12 @@ int kvm_arch_put_registers(CPUState *cs, int level, 
Error **errp)
         return ret;
     }

+    /* Ensure all non-core 0 CPUs are runnable after migration */
+    if ((level == KVM_PUT_FULL_STATE) && (cs->cpu_index != 0)) {
+        RISCVCPU *cpu = RISCV_CPU(cs);
+        ret = kvm_riscv_sync_mpstate_to_kvm(cpu, KVM_MP_STATE_RUNNABLE);
+        if (ret) {
+            return ret;
+        }
+    }

     if (KVM_PUT_RESET_STATE == level) {
         RISCVCPU *cpu = RISCV_CPU(cs);
         if (cs->cpu_index == 0) {
-- 
2.34.1

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