Commit 1c628004 authored by Lorenzo Stoakes's avatar Lorenzo Stoakes Committed by Andrew Morton
Browse files

mm: add mk_vma_flags() bitmap flag macro helper 

This patch introduces the mk_vma_flags() macro helper to allow easy
manipulation of VMA flags utilising the new bitmap representation
implemented of VMA flags defined by the vma_flags_t type.

It is a variadic macro which provides a bitwise-or'd representation of all
of each individual VMA flag specified.

Note that, while we maintain VM_xxx flags for backwards compatibility
until the conversion is complete, we define VMA flags of type vma_flag_t
using VMA_xxx_BIT to avoid confusing the two.

This helper macro therefore can be used thusly:

vma_flags_t flags = mk_vma_flags(VMA_READ_BIT, VMA_WRITE_BIT);

Testing has demonstrated that the compiler optimises this code such that
it generates the same assembly utilising this macro as it does if the
flags were specified manually, for instance:

vma_flags_t get_flags(void)
{
	return mk_vma_flags(VMA_READ_BIT, VMA_WRITE_BIT, VMA_EXEC_BIT);
}

Generates the same code as:

vma_flags_t get_flags(void)
{
	vma_flags_t flags;

	vma_flags_clear_all(&flags);
	vma_flag_set(&flags, VMA_READ_BIT);
	vma_flag_set(&flags, VMA_WRITE_BIT);
	vma_flag_set(&flags, VMA_EXEC_BIT);

	return flags;
}

And:

vma_flags_t get_flags(void)
{
	vma_flags_t flags;
	unsigned long *bitmap = ACCESS_PRIVATE(&flags, __vma_flags);

	*bitmap = 1UL << (__force int)VMA_READ_BIT;
	*bitmap |= 1UL << (__force int)VMA_WRITE_BIT;
	*bitmap |= 1UL << (__force int)VMA_EXEC_BIT;

	return flags;
}

That is:

get_flags:
        movl    $7, %eax
        ret

Link: https://lkml.kernel.org/r/fde00df6ff7fb8c4b42cc0defa5a4924c7a1943a.1769097829.git.lorenzo.stoakes@oracle.com


Signed-off-by: default avatarLorenzo Stoakes <lorenzo.stoakes@oracle.com>
Suggested-by: default avatarJason Gunthorpe <jgg@nvidia.com>
Reviewed-by: default avatarPedro Falcato <pfalcato@suse.de>
Reviewed-by: default avatarLiam R. Howlett <Liam.Howlett@oracle.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Barry Song <baohua@kernel.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Damien Le Moal <dlemoal@kernel.org>
Cc: "Darrick J. Wong" <djwong@kernel.org>
Cc: Jarkko Sakkinen <jarkko@kernel.org>
Cc: Yury Norov <ynorov@nvidia.com>
Cc: Chris Mason <clm@fb.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent e388d312

include/linux/mm.h

+33 −0
Original line number Diff line number Diff line
@@ -2,6 +2,7 @@ 
#ifndef _LINUX_MM_H

#define _LINUX_MM_H



#include <linux/args.h>

#include <linux/errno.h>

#include <linux/mmdebug.h>

#include <linux/gfp.h>
@@ -1026,6 +1027,38 @@ static inline bool vma_test_atomic_flag(struct vm_area_struct *vma, vma_flag_t b 
	return false;

}



/* Set an individual VMA flag in flags, non-atomically. */

static inline void vma_flag_set(vma_flags_t *flags, vma_flag_t bit)

{

	unsigned long *bitmap = flags->__vma_flags;



	__set_bit((__force int)bit, bitmap);

}



static inline vma_flags_t __mk_vma_flags(size_t count, const vma_flag_t *bits)

{

	vma_flags_t flags;

	int i;



	vma_flags_clear_all(&flags);

	for (i = 0; i < count; i++)

		vma_flag_set(&flags, bits[i]);

	return flags;

}



/*

 * Helper macro which bitwise-or combines the specified input flags into a

 * vma_flags_t bitmap value. E.g.:

 *

 * vma_flags_t flags = mk_vma_flags(VMA_IO_BIT, VMA_PFNMAP_BIT,

 * 		VMA_DONTEXPAND_BIT, VMA_DONTDUMP_BIT);

 *

 * The compiler cleverly optimises away all of the work and this ends up being

 * equivalent to aggregating the values manually.

 */

#define mk_vma_flags(...) __mk_vma_flags(COUNT_ARGS(__VA_ARGS__), \

					 (const vma_flag_t []){__VA_ARGS__})



static inline void vma_set_anonymous(struct vm_area_struct *vma)

{

	vma->vm_ops = NULL;