mm: avoid use of BIT() macro for initialising VMA flags

Commit 2b6a3f0 ("mm: declare VMA flags by bit") significantly changed
how VMA flags are declared, utilising an enum of VMA bit values and
ifdef-fery VM_xxx flag declarations via macro.

As part of this change, it uses INIT_VM_FLAG() to define VM_xxx flags from
the newly introduced VMA bit numbers.

However, use of this macro results in apparently unfortunate macro
expansion and resulted in a performance degradation.This appears to be due
to the (__force int), which is required for the sparse typechecking to
work.

Avoid macro expansion issues by simply using 1UL << bitnum.

Link: https://lkml.kernel.org/r/[email protected]
Fixes: 2b6a3f0 ("mm: declare VMA flags by bit")
Signed-off-by: Lorenzo Stoakes <[email protected]>
Reported-by: kernel test robot <[email protected]>
Closes: https://lore.kernel.org/oe-lkp/[email protected]
Cc: Liam Howlett <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Mike Rapoport <[email protected]>
Cc: Suren Baghdasaryan <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: David Laight <[email protected]>
Cc: John Hubbard <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: lorenzo-stoakes

include/linux/mm.h

@@ -395,7 +395,8 @@ enum {
 #undef DECLARE_VMA_BIT
 #undef DECLARE_VMA_BIT_ALIAS
 
-#define INIT_VM_FLAG(name) BIT((__force int) VMA_ ## name ## _BIT)
+#define INIT_VM_FLAG(name) (1UL << (__force int)(VMA_ ## name ## _BIT))
+
 #define VM_READ		INIT_VM_FLAG(READ)
 #define VM_WRITE	INIT_VM_FLAG(WRITE)
 #define VM_EXEC		INIT_VM_FLAG(EXEC)