x86: use CONFIG_PRIVILEGED_STACK_SIZE for stack size

Instead of using CONFIG_MMU_PAGE_SIZE for size of the privileged
stack, use the actual kconfig CONFIG_PRIVILEGED_STACK_SIZE.
This allows for changing the size of privileged stack, and
also aligns to the usage of CONFIG_PRIVILEGED_STACK_SIZE.

Signed-off-by: Daniel Leung <daniel.leung@intel.com>

arch/x86/Kconfig

@@ -489,6 +489,10 @@ config X86_EFI_CONSOLE
 	  Likewise be sure to disable any other console/printk
 	  drivers!
 
+config PRIVILEGED_STACK_SIZE
+	# Must be multiple of CONFIG_MMU_PAGE_SIZE
+	default 4096 if X86_MMU
+
 source "arch/x86/core/Kconfig.ia32"
 source "arch/x86/core/Kconfig.intel64"
 

arch/x86/core/userspace.c

@@ -11,6 +11,9 @@
 #include <ksched.h>
 #include <x86_mmu.h>
 
+BUILD_ASSERT((CONFIG_PRIVILEGED_STACK_SIZE > 0) &&
+	     (CONFIG_PRIVILEGED_STACK_SIZE % CONFIG_MMU_PAGE_SIZE) == 0);
+
 #ifdef CONFIG_DEMAND_PAGING
 #include <zephyr/kernel/mm/demand_paging.h>
 #endif

include/zephyr/arch/x86/thread_stack.h

@@ -66,7 +66,7 @@ struct z_x86_thread_stack_header {
 	char guard_page[CONFIG_MMU_PAGE_SIZE];
 #endif
 #ifdef CONFIG_USERSPACE
-	char privilege_stack[CONFIG_MMU_PAGE_SIZE];
+	char privilege_stack[CONFIG_PRIVILEGED_STACK_SIZE];
 #endif /* CONFIG_USERSPACE */
 } __packed __aligned(Z_X86_STACK_BASE_ALIGN);