OvmfPkg/VirtHstiDxe: add code flash check

Detects qemu config issue: code pflash is writable.
Checked for both PC and Q35.

Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Konstantin Kostiuk <kkostiuk@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Jiewen Yao <Jiewen.yao@intel.com>

OvmfPkg/VirtHstiDxe/VirtHstiDxe.h

@@ -8,6 +8,7 @@ SPDX-License-Identifier: BSD-2-Clause-Patent
 
 #define VIRT_HSTI_BYTE0_SMM_SMRAM_LOCK         BIT0
 #define VIRT_HSTI_BYTE0_SMM_SECURE_VARS_FLASH  BIT1
+#define VIRT_HSTI_BYTE0_READONLY_CODE_FLASH    BIT2
 
 typedef struct {
   // ADAPTER_INFO_PLATFORM_SECURITY
@@ -67,6 +68,18 @@ VirtHstiQemuPCVerify (
   VOID
   );
 
+/* QemuCommon.c */
+
+VOID
+VirtHstiQemuCommonInit (
+  VIRT_ADAPTER_INFO_PLATFORM_SECURITY  *VirtHsti
+  );
+
+VOID
+VirtHstiQemuCommonVerify (
+  VOID
+  );
+
 /* Flash.c */
 
 #define QEMU_FIRMWARE_FLASH_UNKNOWN    0