[RFC PATCH] target/loongarch/kvm: Add software breakpoint support

[Bibo Mao <maobibo@loongson.cn>]

With KVM virtualization, debug exception is passthrough to
to guest kernel rather than host mode. Here hypercall
instruction with special hypercall code is used for sw
breakpoint usage.

Now only software breakpoint is supported, and itt is allowed
to insert/remove software breakpoint. Later hardware  breakpoint
will be added.

Signed-off-by: Bibo Mao <maobibo@loongson.cn>
---
 target/loongarch/kvm/kvm.c | 77 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 77 insertions(+)

diff --git a/target/loongarch/kvm/kvm.c b/target/loongarch/kvm/kvm.c
index c19978a970..49d02076ad 100644
--- a/target/loongarch/kvm/kvm.c
+++ b/target/loongarch/kvm/kvm.c
@@ -29,6 +29,7 @@
 #include "trace.h"
 
 static bool cap_has_mp_state;
+static unsigned int brk_insn;
 const KVMCapabilityInfo kvm_arch_required_capabilities[] = {
     KVM_CAP_LAST_INFO
 };
@@ -675,7 +676,14 @@ static void kvm_loongarch_vm_stage_change(void *opaque, bool running,
 
 int kvm_arch_init_vcpu(CPUState *cs)
 {
+    uint64_t val;
+
     qemu_add_vm_change_state_handler(kvm_loongarch_vm_stage_change, cs);
+
+    if (!kvm_get_one_reg(cs, KVM_REG_LOONGARCH_DEBUG_INST, &val)) {
+        brk_insn = val;
+    }
+
     return 0;
 }
 
@@ -755,6 +763,68 @@ bool kvm_arch_cpu_check_are_resettable(void)
     return true;
 }
 
+
+void kvm_arch_update_guest_debug(CPUState *cpu, struct kvm_guest_debug *dbg)
+{
+    if (kvm_sw_breakpoints_active(cpu)) {
+        dbg->control |= KVM_GUESTDBG_ENABLE | KVM_GUESTDBG_USE_SW_BP;
+    }
+}
+
+int kvm_arch_insert_sw_breakpoint(CPUState *cs, struct kvm_sw_breakpoint *bp)
+{
+    if (cpu_memory_rw_debug(cs, bp->pc, (uint8_t *)&bp->saved_insn, 4, 0) ||
+        cpu_memory_rw_debug(cs, bp->pc, (uint8_t *)&brk_insn, 4, 1)) {
+        error_report("%s failed", __func__);
+        return -EINVAL;
+    }
+    return 0;
+}
+
+int kvm_arch_remove_sw_breakpoint(CPUState *cs, struct kvm_sw_breakpoint *bp)
+{
+    static uint32_t brk;
+
+    if (cpu_memory_rw_debug(cs, bp->pc, (uint8_t *)&brk, 4, 0) ||
+        brk != brk_insn ||
+        cpu_memory_rw_debug(cs, bp->pc, (uint8_t *)&bp->saved_insn, 4, 1)) {
+        error_report("%s failed", __func__);
+        return -EINVAL;
+    }
+    return 0;
+}
+
+int kvm_arch_insert_hw_breakpoint(vaddr addr, vaddr len, int type)
+{
+    return -ENOSYS;
+}
+
+int kvm_arch_remove_hw_breakpoint(vaddr addr, vaddr len, int type)
+{
+    return -ENOSYS;
+}
+
+void kvm_arch_remove_all_hw_breakpoints(void)
+{
+}
+
+static bool kvm_loongarch_handle_debug(CPUState *cs, struct kvm_run *run)
+{
+    LoongArchCPU *cpu = LOONGARCH_CPU(cs);
+    CPULoongArchState *env = &cpu->env;
+
+    kvm_cpu_synchronize_state(cs);
+    if (cs->singlestep_enabled) {
+        return true;
+    }
+
+    if (kvm_find_sw_breakpoint(cs, env->pc)) {
+        return true;
+    }
+
+    return false;
+}
+
 int kvm_arch_handle_exit(CPUState *cs, struct kvm_run *run)
 {
     int ret = 0;
@@ -774,6 +844,13 @@ int kvm_arch_handle_exit(CPUState *cs, struct kvm_run *run)
                          run->iocsr_io.len,
                          run->iocsr_io.is_write);
         break;
+
+    case KVM_EXIT_DEBUG:
+        if (kvm_loongarch_handle_debug(cs, run)) {
+            ret = EXCP_DEBUG;
+        }
+        break;
+
     default:
         ret = -1;
         warn_report("KVM: unknown exit reason %d", run->exit_reason);

base-commit: 5767815218efd3cbfd409505ed824d5f356044ae
-- 
2.39.3