arm64: consolidate rox page protection logic

Consolidate the arm64 decision making for the page protections used
for executable pages, used by both the trampoline code and the kernel
text mapping code.
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://lore.kernel.org/r/E1q9T3v-00EDmW-BH@rmk-PC.armlinux.org.ukSigned-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/mm/mmu.c

@@ -663,12 +663,17 @@ static void __init map_kernel_segment(pgd_t *pgdp, void *va_start, void *va_end,
 	vm_area_add_early(vma);
 }
 
+static pgprot_t kernel_exec_prot(void)
+{
+	return rodata_enabled ? PAGE_KERNEL_ROX : PAGE_KERNEL_EXEC;
+}
+
 #ifdef CONFIG_UNMAP_KERNEL_AT_EL0
 static int __init map_entry_trampoline(void)
 {
 	int i;
 
-	pgprot_t prot = rodata_enabled ? PAGE_KERNEL_ROX : PAGE_KERNEL_EXEC;
+	pgprot_t prot = kernel_exec_prot();
 	phys_addr_t pa_start = __pa_symbol(__entry_tramp_text_start);
 
 	/* The trampoline is always mapped and can therefore be global */
@@ -723,7 +728,7 @@ static void __init map_kernel(pgd_t *pgdp)
 	 * mapping to install SW breakpoints. Allow this (only) when
 	 * explicitly requested with rodata=off.
 	 */
-	pgprot_t text_prot = rodata_enabled ? PAGE_KERNEL_ROX : PAGE_KERNEL_EXEC;
+	pgprot_t text_prot = kernel_exec_prot();
 
 	/*
 	 * If we have a CPU that supports BTI and a kernel built for