TDX doesn't support map different GPAs to same private memory. Thus,
aliasing top 128KB of BIOS as isa-bios is not supported.

On the other hand, TDX guest cannot go to real mode, it can work fine
without isa-bios.

Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
Acked-by: Gerd Hoffmann <kraxel@redhat.com>
---
Changes in v1:
 - update commit message and comment to clarify
---
 hw/i386/x86.c | 25 ++++++++++++++-----------
 1 file changed, 14 insertions(+), 11 deletions(-)

diff --git a/hw/i386/x86.c b/hw/i386/x86.c
index fde5467c4750..2f299355a5e3 100644
--- a/hw/i386/x86.c
+++ b/hw/i386/x86.c
@@ -1170,17 +1170,20 @@ void x86_bios_rom_init(MachineState *ms, const char *default_firmware,
     }
     g_free(filename);
 
-    /* map the last 128KB of the BIOS in ISA space */
-    isa_bios_size = MIN(bios_size, 128 * KiB);
-    isa_bios = g_malloc(sizeof(*isa_bios));
-    memory_region_init_alias(isa_bios, NULL, "isa-bios", bios,
-                             bios_size - isa_bios_size, isa_bios_size);
-    memory_region_add_subregion_overlap(rom_memory,
-                                        0x100000 - isa_bios_size,
-                                        isa_bios,
-                                        1);
-    if (!isapc_ram_fw) {
-        memory_region_set_readonly(isa_bios, true);
+    /* For TDX, alias different GPAs to same private memory is not supported */
+    if (!is_tdx_vm()) {
+        /* map the last 128KB of the BIOS in ISA space */
+        isa_bios_size = MIN(bios_size, 128 * KiB);
+        isa_bios = g_malloc(sizeof(*isa_bios));
+        memory_region_init_alias(isa_bios, NULL, "isa-bios", bios,
+                                bios_size - isa_bios_size, isa_bios_size);
+        memory_region_add_subregion_overlap(rom_memory,
+                                            0x100000 - isa_bios_size,
+                                            isa_bios,
+                                            1);
+        if (!isapc_ram_fw) {
+            memory_region_set_readonly(isa_bios, true);
+        }
     }
 
     /* map all the bios at the top of memory */
-- 
2.34.1