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b=cJVdV6SelfsuOc/iIjycuLFBI9QO16gDia1DU906oY9Ep28XwzavtBGwP1CKqO1tm X/upK8GZWfXwOPQUNWjgYujhlCU/dKGy/emkNdqHKJ0XMZ7PaXR8sJYNhXj9hqI9D/ ZyME1MMPXDUgQ8NnAOe03iLKG9Cg+zhJI10/3snoUD1RmCI9lTpG5pnGS0aoxchhMa IcyGmH8Y+MAoYLste+BY/2DzAg9b/lcDp9hdeiGXuJzGG7MwKqT6aoQcIl8VtBUKkE IxY3sKC+z9AJbANQ4BbLx+Jwf24TU9dGs5cKEe3C3t7IVI88dzcgT4YAnu8JbX48AK PBGH1kAftespA== Date: Thu, 18 Jun 2026 12:35:04 +0300 From: Mike Rapoport To: "David Hildenbrand (Arm)" Cc: Andrew Morton , Linus Torvalds , Alexander Viro , Christian Brauner , Jan Kara , Oleg Nesterov , Peter Xu , vova tokarev , linux-kernel@vger.kernel.org, linux-mm@kvack.org, stable@vger.kernel.org Subject: Re: [PATCH] userfaultfd: prevent registration of special VMAs Message-ID: References: <20260617194059.2529406-1-rppt@kernel.org> <5a993689-f730-406d-8515-8bb6025cc851@kernel.org> <41ef0dce-e973-4947-b5e3-150fdb07f1a6@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam10 X-Rspam-User: X-Stat-Signature: ojzuk41sfuiq19poio9h4epa4bcapuuf X-Rspamd-Queue-Id: 04769140003 X-HE-Tag: 1781775313-693995 X-HE-Meta: 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 SAw1yKsz sPxSYkfwbPcy0d++ytcCsT9o360+0utVIq3y1f0GlZ948SR3IF8rYc93ZXalhrtibPmIkLOJsrS54DtHqbdJs41Bo2rYzulwNb+HPpLBYnto7Ow4hERUPf0oozkep4GOEeeEFqaJKyHGu81maor4GwTma6nm2+syhHoBzkJkIAy50J+Df5fELaIH2twPB2mQhUiAzX5GdIUFSFJRzRdAqZv+v2+DqxF0JP4Biy1kGJtRGED5tw8JFcjxjPsLcIyEJSG/5 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Jun 18, 2026 at 11:25:31AM +0200, David Hildenbrand (Arm) wrote: > On 6/18/26 11:21, Mike Rapoport wrote: > > On Thu, Jun 18, 2026 at 10:47:19AM +0200, David Hildenbrand (Arm) wrote: > >> On 6/18/26 10:43, Mike Rapoport wrote: > >>> > >>> Ah, hugetlb sets VM_DONTEXPAND, so it must me excluded to allow uffd with > >>> hugetlb. > >> > >> It would probably be cleaner to just allow hugetlb, and then check for > >> VM_SPECIAL if not hugetlb. > > > > Cleaner in what sense? > > Will be uglier for sure, just take a look at vma_can_userfault(). > > I was thinking of this: > > diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c > index 180bad42fc79..8a6803618a91 100644 > --- a/mm/userfaultfd.c > +++ b/mm/userfaultfd.c > @@ -2029,7 +2029,10 @@ bool vma_can_userfault(struct vm_area_struct *vma, > vm_flags_t vm_flags, > { > const struct vm_uffd_ops *ops = vma_uffd_ops(vma); > > - if (vma->vm_flags & VM_DROPPABLE) > + if (vma->vm_flags & (VM_DROPPABLE | VM_SHADOW_STACK)) > + return false; > + > + if (!is_vm_hugetlb_page(vma) && (vma->vm_flags & VM_SPECIAL)) > return false; In a way that's an extra check for hugetlb, but it will work. Will respin. > vm_flags &= __VM_UFFD_FLAGS; > > -- > Cheers, > David -- Sincerely yours, Mike.