Re: [PATCH v3 23/40] mm/mlock: clear VMA_LOCKED_MASK over mmap callback

[Lorenzo Stoakes (ARM)]

On Thu, Oct 01, 2026 at 11:20:17AM -0400, Zi Yan wrote:
> On Thu Sep 17, 2026 at 12:22 PM EDT, Lorenzo Stoakes (ARM) wrote:
> > Currently there's a confusing mess around VMA_LOCKED_BIT and
> > VMA_LOCKONFAULT_BIT.
> >
> > It is permitted for drivers to set any flags they like, with the VMA
> > already possessing lock flags.
> >
> > This results in the absurd situation of a VMA possessing both
> > VMA_SPECIAL_FLAGS and VMA_LOCKED_MASK flags, which is not permitted.
> >
> > This has resulted in mlock_vma_folio() having a very silly check for this
> > scenario to work around it.
> >
> > There is no need for this - just clear the flags before invoking the hook
> > and reinstate them afterwards if they are required.
> >
> > Nothing relies upon this being set during the mmap operation.
> >
> > mmap_prepare is unaffected by this so requires no fix.
> >
> > Signed-off-by: Lorenzo Stoakes (ARM) <ljs@xxxxxxxxxx>
> > ---
> >  mm/internal.h |  9 +--------
> >  mm/vma.c      | 14 ++++++++++++++
> >  2 files changed, 15 insertions(+), 8 deletions(-)
> >
> <snip>
>
> > +	/* If VMA flags still valid for locked mask, reinstate. */
> > +	if (vma_supports_mlock(vma)) {
> > +		const vma_flags_t mask =
> > +			vma_flags_and_mask(&map->vma_flags,
> > +					   VMA_LOCKED_MASK);
> > +
> > +		vma_set_flags_mask(vma, mask);
>
> It took me a while to figure out vma_set_flags_mask() is an OR
> operation.

Yeah naming is hard :)

Let me add a comment here though because it's kinda a bit unusual.

>
> > +	}
> > +
> >  	map->vma_flags = vma->flags;
> >
> >  	return 0;
>
> Otherwise, LGTM.
>
> Reviewed-by: Zi Yan <ziy@xxxxxxxxxx>

Thanks!

>
>
>
> --
> Best Regards,
> Yan, Zi
>

--
Cheers, Lorenzo