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

Pedro Falcato
2026-02-06T17:14:18Z

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 <lorenzo.stoakes@oracle.com>

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

--
Pedro