[PATCH v4 2/2] riscv: patch: skip fixmap mapping when kernel text is already writable

[Xiaofeng Yuan <xiaofengmian@163.com>]

Currently patch_map() always creates a temporary writable mapping via
fixmap for kernel text addresses, even when CONFIG_STRICT_MODULE_RWX
is disabled and the kernel text is already mapped with _PAGE_WRITE.

This is unnecessary overhead at best, and on minimal configurations
it can cause page faults.

Skip the fixmap path for kernel text when CONFIG_STRICT_MODULE_RWX
is not enabled, since the text pages are already writable in this case.

Signed-off-by: Xiaofeng Yuan <xiaofengmian@163.com>
---
v2: add commit description
v3: early return when !CONFIG_STRICT_MODULE_RWX (per Nam Cao's suggestion)
diff --git a/arch/riscv/kernel/patch.c b/arch/riscv/kernel/patch.c
index 16b243376f..caef41d5ef 100644
--- a/arch/riscv/kernel/patch.c
+++ b/arch/riscv/kernel/patch.c
@@ -44,15 +44,16 @@ static __always_inline void *patch_map(void *addr, const unsigned int fixmap)
 	uintptr_t uintaddr = (uintptr_t) addr;
 	phys_addr_t phys;
 
+	if (!IS_ENABLED(CONFIG_STRICT_MODULE_RWX))
+		return addr;
+
 	if (core_kernel_text(uintaddr) || is_kernel_exittext(uintaddr)) {
 		phys = __pa_symbol(addr);
-	} else if (IS_ENABLED(CONFIG_STRICT_MODULE_RWX)) {
+	} else {
 		struct page *page = vmalloc_to_page(addr);
 
 		BUG_ON(!page);
 		phys = page_to_phys(page) + offset_in_page(addr);
-	} else {
-		return addr;
 	}
 
 	return (void *)set_fixmap_offset(fixmap, phys);
-- 
2.43.0