riscv: Fix set_direct_map_default_noflush() to reset _PAGE_EXEC

When resetting the linear mapping permissions, we must make sure that we
clear the X bit so that do not end up with WX mappings (since we set
PAGE_KERNEL).

Fixes: 395a21ff ("riscv: add ARCH_HAS_SET_DIRECT_MAP support")
Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Link: https://lore.kernel.org/r/20231213134027.155327-3-alexghiti@rivosinc.comSigned-off-by: Palmer Dabbelt <palmer@rivosinc.com>

arch/riscv/mm/pageattr.c

@@ -383,7 +383,7 @@ int set_direct_map_invalid_noflush(struct page *page)
 int set_direct_map_default_noflush(struct page *page)
 {
 	return __set_memory((unsigned long)page_address(page), 1,
-			    PAGE_KERNEL, __pgprot(0));
+			    PAGE_KERNEL, __pgprot(_PAGE_EXEC));
 }
 
 #ifdef CONFIG_DEBUG_PAGEALLOC