On Sun, Aug 23, 2026 at 03:17:40PM +0300, Mike Rapoport (Microsoft) wrote:
> Move userfaultfd_{missing,wp,minor,rwp}() and userfaultfd_protected()
> ahead of uffd_disable_huge_pmd_share() and uffd_disable_fault_around()
> and make the latter two use the helpers rather than open coded VMA flag
> masks.
>
> Convert open coded VMA flag test in mfill_get_vma() to userfaultfd_wp()
> as well.It'd be better to do the moves and the reworks separately. We don't have a limit on patch count :) > > With every user of the per-VMA uffd modes going through the helpers, > their underlying representation can be changed in the next step. > > No functional change. There is a functional change, or at least seems to be, see below. > > Assisted-by: copilot:claude-opus-5 > Signed-off-by: Mike Rapoport (Microsoft) <[email protected]> > --- > include/linux/userfaultfd_k.h | 70 > +++++++++++++++++++++---------------------- > mm/userfaultfd.c | 2 +- > 2 files changed, 35 insertions(+), 37 deletions(-) > > diff --git a/include/linux/userfaultfd_k.h b/include/linux/userfaultfd_k.h > index 3396d270b159..d8262e3dc134 100644 > --- a/include/linux/userfaultfd_k.h > +++ b/include/linux/userfaultfd_k.h > @@ -168,42 +168,6 @@ static inline bool > is_mergeable_vm_userfaultfd_ctx(struct vm_area_struct *vma, > return vma->vm_userfaultfd_ctx.ctx == vm_ctx.ctx; > } > > -/* > - * Never enable huge pmd sharing on some uffd registered vmas: > - * > - * - VM_UFFD_WP and VM_UFFD_RWP VMAs, because the write protect / access > - * tracking information is per pgtable entry. > - * > - * - VM_UFFD_MINOR VMAs, because otherwise we would never get minor faults > for > - * VMAs which share huge pmds. (If you have two mappings to the same > - * underlying pages, and fault in the non-UFFD-registered one with a write, > - * with huge pmd sharing this would *also* setup the second UFFD-registered > - * mapping, and we'd not get minor faults.) > - */ > -static inline bool uffd_disable_huge_pmd_share(struct vm_area_struct *vma) > -{ > - return vma_test_any_mask(vma, > - mk_vma_flags_from_masks(VMA_UFFD_WP, VMA_UFFD_RWP, > - VMA_UFFD_MINOR)); > -} > - > -/* > - * Don't do fault around for WP, RWP or MINOR registered uffd range. For > - * MINOR registered range, fault around will be a total disaster and ptes can > - * be installed without notifications; for WP it should mostly be fine as > long > - * as the fault around checks for pte_none() before the installation, however > - * to be super safe we just forbid it; for RWP, pre-faulted neighbours would > - * be indistinguishable from accessed pages in PAGEMAP_SCAN > (PAGE_IS_ACCESSED) > - * and pollute the tracked working set, so each page must be populated by its > - * own fault. > - */ > -static inline bool uffd_disable_fault_around(struct vm_area_struct *vma) > -{ > - return vma_test_any_mask(vma, > - mk_vma_flags_from_masks(VMA_UFFD_WP, VMA_UFFD_RWP, > - VMA_UFFD_MINOR)); > -} > - > static inline bool userfaultfd_missing(const struct vm_area_struct *vma) > { > return vma_test_any_mask(vma, VMA_UFFD_MISSING); > @@ -235,6 +199,40 @@ static inline bool userfaultfd_protected(const struct > vm_area_struct *vma) > return userfaultfd_wp(vma) || userfaultfd_rwp(vma); > } > > +/* > + * Never enable huge pmd sharing on some uffd registered vmas: > + * > + * - uffd-WP and uffd-RWP VMAs, because the write protect / access tracking > + * information is per pgtable entry. > + * > + * - uffd-MINOR VMAs, because otherwise we would never get minor faults for > + * VMAs which share huge pmds. (If you have two mappings to the same > + * underlying pages, and fault in the non-UFFD-registered one with a write, > + * with huge pmd sharing this would *also* setup the second UFFD-registered > + * mapping, and we'd not get minor faults.) > + */ > +static inline bool uffd_disable_huge_pmd_share(struct vm_area_struct *vma) > +{ > + return userfaultfd_minor(vma) || userfaultfd_wp(vma) || > + userfaultfd_rwp(vma); > +} > + > +/* > + * Don't do fault around for WP, RWP or MINOR registered uffd range. For > + * MINOR registered range, fault around will be a total disaster and ptes can > + * be installed without notifications; for WP it should mostly be fine as > long > + * as the fault around checks for pte_none() before the installation, however > + * to be super safe we just forbid it; for RWP, pre-faulted neighbours would > + * be indistinguishable from accessed pages in PAGEMAP_SCAN > (PAGE_IS_ACCESSED) > + * and pollute the tracked working set, so each page must be populated by its > + * own fault. > + */ > +static inline bool uffd_disable_fault_around(struct vm_area_struct *vma) > +{ > + return userfaultfd_minor(vma) || userfaultfd_wp(vma) || > + userfaultfd_rwp(vma); This is changing the logic. Before we were testing only the flags, now we have: static inline bool userfaultfd_rwp(const struct vm_area_struct *vma) { /* * Callers gate PAGE_NONE usage on this; PAGE_NONE is a BUILD_BUG() * without CONFIG_ARCH_HAS_PTE_PROTNONE, so fold to false. */ if (!IS_ENABLED(CONFIG_ARCH_HAS_PTE_PROTNONE)) return false; return vma_test_single_mask(vma, VMA_UFFD_RWP); } I.e. adding in a CONFIG_ARCH_HAS_PTE_PROTNONE check. BTW side-note these: static inline bool userfaultfd_missing(const struct vm_area_struct *vma) { return vma_test_any_mask(vma, VMA_UFFD_MISSING); } static inline bool userfaultfd_wp(const struct vm_area_struct *vma) { return vma_test_any_mask(vma, VMA_UFFD_WP); } static inline bool userfaultfd_minor(const struct vm_area_struct *vma) { return vma_test_any_mask(vma, VMA_UFFD_MINOR); } Should all use vma_test_single_mask() really :) > +} > + > static inline bool userfaultfd_pte_wp(struct vm_area_struct *vma, > pte_t pte) > { > diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c > index 74f04c323c50..32003aa04943 100644 > --- a/mm/userfaultfd.c > +++ b/mm/userfaultfd.c > @@ -261,7 +261,7 @@ static int mfill_get_vma(struct mfill_state *state) > * validate 'mode' now that we know the dst_vma: don't allow > * a wrprotect copy if the userfaultfd didn't register as WP. > */ > - if ((flags & MFILL_ATOMIC_WP) && !(dst_vma->vm_flags & VM_UFFD_WP)) > + if ((flags & MFILL_ATOMIC_WP) && !userfaultfd_wp(dst_vma)) > goto out_unlock; > > if (is_vm_hugetlb_page(dst_vma)) > > -- > 2.53.0 > -- Cheers, Lorenzo
