Re: [RFC PATCH v3 17/36] pflash_cfi01/tdx: Introduce ram_mode of pflash for TDVF

[Gerd Hoffmann]

  Hi,

> At the time I did try a gross hack that (IIRC) disabled the
> rom_reset logic, and munged x86_bios_rom_init so that it would
> force load it straight at the RAM location.

Sounds reasonable.  The whole rom logic exists to handle resets,
but with confidential guests we don't need that, we can't change
guest state to perform a reset anyway ...

take care,
  Gerd

diff --git a/hw/i386/x86.c b/hw/i386/x86.c
index 4cf107baea34..169ef96682de 100644
--- a/hw/i386/x86.c
+++ b/hw/i386/x86.c
@@ -1115,15 +1115,26 @@ void x86_bios_rom_init(MachineState *ms, const char 
*default_firmware,
         goto bios_error;
     }
     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) {
-    bios_error:
-        fprintf(stderr, "qemu: could not load PC BIOS '%s'\n", bios_name);
-        exit(1);
+    if (1 /* confidential computing */) {
+        /*
+         * 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);
+    } 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);
 
@@ -1144,6 +1155,11 @@ void x86_bios_rom_init(MachineState *ms, const char 
*default_firmware,
     memory_region_add_subregion(rom_memory,
                                 (uint32_t)(-bios_size),
                                 bios);
+    return;
+
+bios_error:
+    fprintf(stderr, "qemu: could not load PC BIOS '%s'\n", bios_name);
+    exit(1);
 }
 
 bool x86_machine_is_smm_enabled(const X86MachineState *x86ms)