Re: [PATCH v2 03/13] mm: add mk_vma_flags() bitmap flag macro helper

On Thu, Jan 22, 2026 at 04:06:12PM +0000, Lorenzo Stoakes wrote:

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);

We allow for up to 5 flags to specified at a time which should accommodate
all current kernel uses of combined VMA flags.

How do you allow up to 5 flags? I don't see any such limitation in the code?
 

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

Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Lorenzo Stoakes <redacted>

Reviewed-by: Pedro Falcato <pfalcato@suse.de>

-- 
Pedro