[PATCH 4/7] maccess: Use a scoped guard for page faults

[Muhammad Usama Anjum]

Kernel nofault copy and string paths open-code page-fault disable and
enable around label-based loops, duplicating cleanup on success and
failure.

Use a page-fault scope guard instead. Leaving the scope now re-enables
page faults on both paths without separate cleanup at the fault label.

No functional change.

Signed-off-by: Muhammad Usama Anjum <usama.anjum@xxxxxxx>
---
 mm/maccess.c | 53 +++++++++++++++++++++++++---------------------------
 1 file changed, 25 insertions(+), 28 deletions(-)

diff --git a/mm/maccess.c b/mm/maccess.c
index c59a0e092d24a..f695ceefe6fcc 100644
--- a/mm/maccess.c
+++ b/mm/maccess.c
@@ -38,18 +38,17 @@ long copy_from_kernel_nofault(void *dst, const void *src, size_t size)
 	if (!size)
 		return 0;
 
-	pagefault_disable();
-	if (!(align & 7))
-		copy_from_kernel_nofault_loop(dst, src, size, u64, Efault);
-	if (!(align & 3))
-		copy_from_kernel_nofault_loop(dst, src, size, u32, Efault);
-	if (!(align & 1))
-		copy_from_kernel_nofault_loop(dst, src, size, u16, Efault);
-	copy_from_kernel_nofault_loop(dst, src, size, u8, Efault);
-	pagefault_enable();
+	scoped_guard(pagefault) {
+		if (!(align & 7))
+			copy_from_kernel_nofault_loop(dst, src, size, u64, Efault);
+		if (!(align & 3))
+			copy_from_kernel_nofault_loop(dst, src, size, u32, Efault);
+		if (!(align & 1))
+			copy_from_kernel_nofault_loop(dst, src, size, u16, Efault);
+		copy_from_kernel_nofault_loop(dst, src, size, u8, Efault);
+	}
 	return 0;
 Efault:
-	pagefault_enable();
 	return -EFAULT;
 }
 EXPORT_SYMBOL_GPL(copy_from_kernel_nofault);
@@ -73,18 +72,17 @@ long copy_to_kernel_nofault(void *dst, const void *src, size_t size)
 	if (!IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS))
 		align = (unsigned long)dst | (unsigned long)src;
 
-	pagefault_disable();
-	if (!(align & 7))
-		copy_to_kernel_nofault_loop(dst, src, size, u64, Efault);
-	if (!(align & 3))
-		copy_to_kernel_nofault_loop(dst, src, size, u32, Efault);
-	if (!(align & 1))
-		copy_to_kernel_nofault_loop(dst, src, size, u16, Efault);
-	copy_to_kernel_nofault_loop(dst, src, size, u8, Efault);
-	pagefault_enable();
+	scoped_guard(pagefault) {
+		if (!(align & 7))
+			copy_to_kernel_nofault_loop(dst, src, size, u64, Efault);
+		if (!(align & 3))
+			copy_to_kernel_nofault_loop(dst, src, size, u32, Efault);
+		if (!(align & 1))
+			copy_to_kernel_nofault_loop(dst, src, size, u16, Efault);
+		copy_to_kernel_nofault_loop(dst, src, size, u8, Efault);
+	}
 	return 0;
 Efault:
-	pagefault_enable();
 	return -EFAULT;
 }
 
@@ -97,18 +95,17 @@ long strncpy_from_kernel_nofault(char *dst, const void *unsafe_addr, long count)
 	if (!copy_from_kernel_nofault_allowed(unsafe_addr, count))
 		return -ERANGE;
 
-	pagefault_disable();
-	do {
-		__get_kernel_nofault(dst, src, u8, Efault);
-		dst++;
-		src++;
-	} while (dst[-1] && src - unsafe_addr < count);
-	pagefault_enable();
+	scoped_guard(pagefault) {
+		do {
+			__get_kernel_nofault(dst, src, u8, Efault);
+			dst++;
+			src++;
+		} while (dst[-1] && src - unsafe_addr < count);
+	}
 
 	dst[-1] = '\0';
 	return src - unsafe_addr;
 Efault:
-	pagefault_enable();
 	dst[0] = '\0';
 	return -EFAULT;
 }
-- 
2.47.3