Hi Peter, On Mon, Feb 02, 2026 at 04:49:09PM -0500, Peter Xu wrote: > Hi, Mike, > > On Tue, Jan 27, 2026 at 09:29:23PM +0200, Mike Rapoport wrote: > > From: "Mike Rapoport (Microsoft)" <[email protected]> > > > > Split the code that finds, locks and verifies VMA from mfill_atomic() > > into a helper function. > > > > This function will be used later during refactoring of > > mfill_atomic_pte_copy(). > > > > Add a counterpart mfill_put_vma() helper that unlocks the VMA and > > releases map_changing_lock. > > > > Signed-off-by: Mike Rapoport (Microsoft) <[email protected]> > > --- > > mm/userfaultfd.c | 124 ++++++++++++++++++++++++++++------------------- > > 1 file changed, 73 insertions(+), 51 deletions(-) > > > > diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c > > index 9dd285b13f3b..45d8f04aaf4f 100644 > > --- a/mm/userfaultfd.c > > +++ b/mm/userfaultfd.c > > @@ -157,6 +157,73 @@ static void uffd_mfill_unlock(struct vm_area_struct > > *vma) > > } > > #endif > > > > +static void mfill_put_vma(struct mfill_state *state) > > +{ > > + up_read(&state->ctx->map_changing_lock); > > + uffd_mfill_unlock(state->vma); > > + state->vma = NULL; > > +} > > + > > +static int mfill_get_vma(struct mfill_state *state) > > +{ > > + struct userfaultfd_ctx *ctx = state->ctx; > > + uffd_flags_t flags = state->flags; > > + struct vm_area_struct *dst_vma; > > + int err; > > + > > + /* > > + * Make sure the vma is not shared, that the dst range is > > + * both valid and fully within a single existing vma. > > + */ > > + dst_vma = uffd_mfill_lock(ctx->mm, state->dst_start, state->len); > > + if (IS_ERR(dst_vma)) > > + return PTR_ERR(dst_vma); > > + > > + /* > > + * If memory mappings are changing because of non-cooperative > > + * operation (e.g. mremap) running in parallel, bail out and > > + * request the user to retry later > > + */ > > + down_read(&ctx->map_changing_lock); > > + err = -EAGAIN; > > + if (atomic_read(&ctx->mmap_changing)) > > + goto out_unlock; > > + > > + err = -EINVAL; > > + > > + /* > > + * shmem_zero_setup is invoked in mmap for MAP_ANONYMOUS|MAP_SHARED but > > + * it will overwrite vm_ops, so vma_is_anonymous must return false. > > + */ > > + if (WARN_ON_ONCE(vma_is_anonymous(dst_vma) && > > + dst_vma->vm_flags & VM_SHARED)) > > + goto out_unlock; > > + > > + /* > > + * 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)) > > + goto out_unlock; > > + > > + if (is_vm_hugetlb_page(dst_vma)) > > + goto out; > > + > > + if (!vma_is_anonymous(dst_vma) && !vma_is_shmem(dst_vma)) > > + goto out_unlock; > > + if (!vma_is_shmem(dst_vma) && > > + uffd_flags_mode_is(flags, MFILL_ATOMIC_CONTINUE)) > > + goto out_unlock; > > IMHO it's a bit weird to check for vma permissions in a get_vma() function. > > Also, in the follow up patch it'll be also reused in > mfill_copy_folio_retry() which doesn't need to check vma permission. > > Maybe we can introduce mfill_vma_check() for these two checks? Then we can > also drop the slightly weird is_vm_hugetlb_page() check (and "out" label) > above.
This version of get_vma() keeps the checks exactly as they were when we were retrying after dropping the lock and I prefer to have them this way to begin with. Later we can optimize this further after the dust settles after these changes. -- Sincerely yours, Mike.
