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. Reviewed-by: Zi Yan <[email protected]> Signed-off-by: Lorenzo Stoakes (ARM) <[email protected]> --- mm/internal.h | 9 +-------- mm/vma.c | 17 +++++++++++++++++ 2 files changed, 18 insertions(+), 8 deletions(-) diff --git a/mm/internal.h b/mm/internal.h index 557e629db8c5..4ae08fedffff 100644 --- a/mm/internal.h +++ b/mm/internal.h @@ -970,14 +970,7 @@ void mlock_folio(struct folio *folio); static inline void mlock_vma_folio(struct folio *folio, struct vm_area_struct *vma) { - /* - * The VM_SPECIAL check here serves two purposes. - * 1) VM_IO check prevents migration from double-counting during mlock. - * 2) Although mmap_region() and mlock_fixup() take care that VM_LOCKED - * is never left set on a VM_SPECIAL vma, there is an interval while - * file->f_op->mmap() is using vm_insert_page(s), when VM_LOCKED may - * still be set while VM_SPECIAL bits are added: so ignore it then. - */ + /* The VM_IO check prevents migration from double-counting during mlock. */ if (unlikely((vma->vm_flags & (VM_LOCKED|VM_SPECIAL)) == VM_LOCKED)) mlock_folio(folio); } diff --git a/mm/vma.c b/mm/vma.c index 90fe6f0ee3b1..df2efdfa3805 100644 --- a/mm/vma.c +++ b/mm/vma.c @@ -2607,6 +2607,11 @@ static int __mmap_new_file_vma(struct mmap_state *map, if (!map->vm_file->f_op->mmap) return 0; + /* + * Driver-specified flags may make the lock flags invalid, so clear + * VMA_LOCKED_MASK and reinstate it afterwards if appropriate. + */ + vma_clear_flags_mask(vma, VMA_LOCKED_MASK); error = mmap_file(vma->vm_file, vma); map->vm_file = vma->vm_file; @@ -2626,6 +2631,18 @@ static int __mmap_new_file_vma(struct mmap_state *map, return error; } + /* + * If the VMA is still eligible for mlock(), reinstate any original + * VMA_LOCKED_BIT and/or VMA_LOCKONFAULT_BIT flags. + */ + 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); + } + map->vma_flags = vma->flags; return 0; -- 2.55.0
