From: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Date: Fri, 2 Jul 2021 16:48:22 +0530
Subject: bitops: Add non-atomic bitops for pointers
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
Patch-mainline: v5.15-rc1
Git-commit: cb0f80039fb7ec9981a74d22019daaa85ff51a3d
References: jsc#PED-1565

cpumap needs to set, clear, and test the lowest bit in skb pointer in
various places. To make these checks less noisy, add pointer friendly
bitop macros that also do some typechecking to sanitize the argument.

These wrap the non-atomic bitops __set_bit, __clear_bit, and test_bit
but for pointer arguments. Pointer's address has to be passed in and it
is treated as an unsigned long *, since width and representation of
pointer and unsigned long match on targets Linux supports. They are
prefixed with double underscore to indicate lack of atomicity.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Reviewed-by: Toke Høiland-Jørgensen <toke@redhat.com>
Link: https://lore.kernel.org/bpf/20210702111825.491065-3-memxor@gmail.com
Acked-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
---
 include/linux/bitops.h    |   50 ++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/typecheck.h |    9 ++++++++
 2 files changed, 59 insertions(+)

--- a/include/linux/bitops.h
+++ b/include/linux/bitops.h
@@ -4,6 +4,7 @@
 
 #include <asm/types.h>
 #include <linux/bits.h>
+#include <linux/typecheck.h>
 
 #include <uapi/linux/kernel.h>
 
@@ -253,6 +254,55 @@ static __always_inline void __assign_bit
 		__clear_bit(nr, addr);
 }
 
+/**
+ * __ptr_set_bit - Set bit in a pointer's value
+ * @nr: the bit to set
+ * @addr: the address of the pointer variable
+ *
+ * Example:
+ *	void *p = foo();
+ *	__ptr_set_bit(bit, &p);
+ */
+#define __ptr_set_bit(nr, addr)                         \
+	({                                              \
+		typecheck_pointer(*(addr));             \
+		__set_bit(nr, (unsigned long *)(addr)); \
+	})
+
+/**
+ * __ptr_clear_bit - Clear bit in a pointer's value
+ * @nr: the bit to clear
+ * @addr: the address of the pointer variable
+ *
+ * Example:
+ *	void *p = foo();
+ *	__ptr_clear_bit(bit, &p);
+ */
+#define __ptr_clear_bit(nr, addr)                         \
+	({                                                \
+		typecheck_pointer(*(addr));               \
+		__clear_bit(nr, (unsigned long *)(addr)); \
+	})
+
+/**
+ * __ptr_test_bit - Test bit in a pointer's value
+ * @nr: the bit to test
+ * @addr: the address of the pointer variable
+ *
+ * Example:
+ *	void *p = foo();
+ *	if (__ptr_test_bit(bit, &p)) {
+ *	        ...
+ *	} else {
+ *		...
+ *	}
+ */
+#define __ptr_test_bit(nr, addr)                       \
+	({                                             \
+		typecheck_pointer(*(addr));            \
+		test_bit(nr, (unsigned long *)(addr)); \
+	})
+
 #ifdef __KERNEL__
 
 #ifndef set_mask_bits
--- a/include/linux/typecheck.h
+++ b/include/linux/typecheck.h
@@ -22,4 +22,13 @@
 	(void)__tmp; \
 })
 
+/*
+ * Check at compile time that something is a pointer type.
+ */
+#define typecheck_pointer(x) \
+({	typeof(x) __dummy; \
+	(void)sizeof(*__dummy); \
+	1; \
+})
+
 #endif		/* TYPECHECK_H_INCLUDED */