i386: firmware parsing and sev setup for -bios loaded firmware

Don't register firmware as rom, not needed (see comment).
Add x86_firmware_configure() call for proper sev initialization.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Tested-by: Xiaoyao Li <xiaoyao.li@intel.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Tested-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Message-Id: <20220425135051.551037-4-kraxel@redhat.com>

hw/i386/x86.c

@@ -1115,12 +1115,25 @@ void x86_bios_rom_init(MachineState *ms, const char *default_firmware,
     }
     bios = g_malloc(sizeof(*bios));
     memory_region_init_ram(bios, NULL, "pc.bios", bios_size, &error_fatal);
-    if (!isapc_ram_fw) {
-        memory_region_set_readonly(bios, true);
-    }
-    ret = rom_add_file_fixed(bios_name, (uint32_t)(-bios_size), -1);
-    if (ret != 0) {
-        goto bios_error;
+    if (sev_enabled()) {
+        /*
+         * The concept of a "reset" simply doesn't exist for
+         * confidential computing guests, we have to destroy and
+         * re-launch them instead.  So there is no need to register
+         * the firmware as rom to properly re-initialize on reset.
+         * Just go for a straight file load instead.
+         */
+        void *ptr = memory_region_get_ram_ptr(bios);
+        load_image_size(filename, ptr, bios_size);
+        x86_firmware_configure(ptr, bios_size);
+    } else {
+        if (!isapc_ram_fw) {
+            memory_region_set_readonly(bios, true);
+        }
+        ret = rom_add_file_fixed(bios_name, (uint32_t)(-bios_size), -1);
+        if (ret != 0) {
+            goto bios_error;
+        }
     }
     g_free(filename);