acpi: Set proper maximum size for "etc/acpi/rsdp" blob

Let's also set a maximum size for "etc/acpi/rsdp", so the maximum
size doesn't get implicitly set based on the initial table size. In my
experiments, the table size was in the range of 22 bytes, so a single
page (== what we used until now) seems to be good enough.

Now that we have defined maximum sizes for all currently used table types,
let's assert that we catch usage with new tables that need a proper maximum
size definition.

Also assert that our initial size does not exceed the maximum size; while
qemu_ram_alloc_internal() properly asserts that the initial RAMBlock size
is <= its maximum size, the result might differ when the host page size
is bigger than 4k.

Suggested-by: Laszlo Ersek <lersek@redhat.com>
Cc: Alistair Francis <alistair.francis@xilinx.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Igor Mammedov <imammedo@redhat.com>
Cc: Peter Maydell <peter.maydell@linaro.org>
Cc: Shannon Zhao <shannon.zhaosl@gmail.com>
Cc: Marcel Apfelbaum <marcel.apfelbaum@gmail.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Richard Henderson <richard.henderson@linaro.org>
Cc: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20210304105554.121674-5-david@redhat.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/acpi/utils.c

@@ -29,14 +29,19 @@
 MemoryRegion *acpi_add_rom_blob(FWCfgCallback update, void *opaque,
                                 GArray *blob, const char *name)
 {
-    uint64_t max_size = 0;
+    uint64_t max_size;
 
     /* Reserve RAM space for tables: add another order of magnitude. */
     if (!strcmp(name, ACPI_BUILD_TABLE_FILE)) {
         max_size = 0x200000;
     } else if (!strcmp(name, ACPI_BUILD_LOADER_FILE)) {
         max_size = 0x10000;
+    } else if (!strcmp(name, ACPI_BUILD_RSDP_FILE)) {
+        max_size = 0x1000;
+    } else {
+        g_assert_not_reached();
     }
+    g_assert(acpi_data_len(blob) <= max_size);
 
     return rom_add_blob(name, blob->data, acpi_data_len(blob), max_size, -1,
                         name, update, opaque, NULL, true);