i386/tdx: Handle KVM_SYSTEM_EVENT_TDX_FATAL

TD guest can use TDG.VP.VMCALL<REPORT_FATAL_ERROR> to request
termination. KVM translates such request into KVM_EXIT_SYSTEM_EVENT with
type of KVM_SYSTEM_EVENT_TDX_FATAL.

Add hanlder for such exit. Parse and print the error message, and
terminate the TD guest in the handler.

Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
Reviewed-by: Zhao Liu <zhao1.liu@intel.com>
Link: https://lore.kernel.org/r/20250508150002.689633-29-xiaoyao.li@intel.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

target/i386/kvm/kvm.c

@@ -6129,6 +6129,16 @@ int kvm_arch_handle_exit(CPUState *cs, struct kvm_run *run)
     case KVM_EXIT_HYPERCALL:
         ret = kvm_handle_hypercall(run);
         break;
+    case KVM_EXIT_SYSTEM_EVENT:
+        switch (run->system_event.type) {
+        case KVM_SYSTEM_EVENT_TDX_FATAL:
+            ret = tdx_handle_report_fatal_error(cpu, run);
+            break;
+        default:
+            ret = -1;
+            break;
+        }
+        break;
     default:
         fprintf(stderr, "KVM: unknown exit reason %d\n", run->exit_reason);
         ret = -1;

target/i386/kvm/tdx-stub.c

@@ -13,3 +13,8 @@ int tdx_parse_tdvf(void *flash_ptr, int size)
 {
     return -EINVAL;
 }
+
+int tdx_handle_report_fatal_error(X86CPU *cpu, struct kvm_run *run)
+{
+    return -EINVAL;
+}

target/i386/kvm/tdx.c

@@ -615,6 +615,52 @@ int tdx_parse_tdvf(void *flash_ptr, int size)
     return tdvf_parse_metadata(&tdx_guest->tdvf, flash_ptr, size);
 }
 
+/*
+ * Only 8 registers can contain valid ASCII byte stream to form the fatal
+ * message, and their sequence is: R14, R15, RBX, RDI, RSI, R8, R9, RDX
+ */
+#define TDX_FATAL_MESSAGE_MAX        64
+
+int tdx_handle_report_fatal_error(X86CPU *cpu, struct kvm_run *run)
+{
+    uint64_t error_code = run->system_event.data[R_R12];
+    uint64_t reg_mask = run->system_event.data[R_ECX];
+    char *message = NULL;
+    uint64_t *tmp;
+
+    if (error_code & 0xffff) {
+        error_report("TDX: REPORT_FATAL_ERROR: invalid error code: 0x%lx",
+                     error_code);
+        return -1;
+    }
+
+    if (reg_mask) {
+        message = g_malloc0(TDX_FATAL_MESSAGE_MAX + 1);
+        tmp = (uint64_t *)message;
+
+#define COPY_REG(REG)                               \
+    do {                                            \
+        if (reg_mask & BIT_ULL(REG)) {              \
+            *(tmp++) = run->system_event.data[REG]; \
+        }                                           \
+    } while (0)
+
+        COPY_REG(R_R14);
+        COPY_REG(R_R15);
+        COPY_REG(R_EBX);
+        COPY_REG(R_EDI);
+        COPY_REG(R_ESI);
+        COPY_REG(R_R8);
+        COPY_REG(R_R9);
+        COPY_REG(R_EDX);
+        *((char *)tmp) = '\0';
+    }
+#undef COPY_REG
+
+    error_report("TD guest reports fatal error. %s", message ? : "");
+    return -1;
+}
+
 static bool tdx_guest_get_sept_ve_disable(Object *obj, Error **errp)
 {
     TdxGuest *tdx = TDX_GUEST(obj);

target/i386/kvm/tdx.h

@@ -8,6 +8,7 @@
 #endif
 
 #include "confidential-guest.h"
+#include "cpu.h"
 #include "hw/i386/tdvf.h"
 
 #define TYPE_TDX_GUEST "tdx-guest"
@@ -59,5 +60,6 @@ bool is_tdx_vm(void);
 int tdx_pre_create_vcpu(CPUState *cpu, Error **errp);
 void tdx_set_tdvf_region(MemoryRegion *tdvf_mr);
 int tdx_parse_tdvf(void *flash_ptr, int size);
+int tdx_handle_report_fatal_error(X86CPU *cpu, struct kvm_run *run);
 
 #endif /* QEMU_I386_TDX_H */