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b=HqcFCLD2R7hOPyjhYBm4FaxGAnBpbYMYsFLx0Rjd25jHKkJQddurK3Np5tnW8tQnD wtH+hrqqAk2HAIDBuyFeTeBMWB7wFiahcrOzeI/WDHGggbHSAgB0gJpcp8RIhAFzV8 T2LL+Sdv4oZNhqxs0NOyq52BjPpfnhH/DCgXFb1a9vLxXMVlCyHqWxKw1KnQyhHGuI e0FpI30Wn9FRg4lHhC7CqxWBjI5Ud89E9brojrzTJ00EeCMstn8cZ51Wn9mnR6gU+i DciK8JXWruf9KN8NLBYpfROTQvxApSrQf/uiz0E7zuCjThV3UgZSwRYnqrl4i3DM9g QgTsA3/BrCoHQ== Message-ID: <11bae87d-73e6-4946-a41f-c5542fb40b75@kernel.org> Date: Thu, 18 Jun 2026 11:37:10 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] userfaultfd: prevent registration of special VMAs To: Mike Rapoport 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 References: <20260617194059.2529406-1-rppt@kernel.org> <5a993689-f730-406d-8515-8bb6025cc851@kernel.org> <41ef0dce-e973-4947-b5e3-150fdb07f1a6@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam10 X-Rspam-User: X-Stat-Signature: sk7xbzrxhh7zhekp3wdy83cjtiep5dfi X-Rspamd-Queue-Id: 7130A18000B X-HE-Tag: 1781775436-549518 X-HE-Meta: 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 thK1lkcR mrsIu/QpM7FBz4GeXaW5VSY0DgZ78v/jOSue/3Ri+MeAZ13KoRepPc3wJZ0b0WRxmfoQNf1jr3CuwMWqKAxcn2BWuq//gddETuybHGj/yzrTTrNDGmo8kGBxcvHWROj2fFbn6utBFWOfei2hdNFyvHB2hfbvvoC0UYxqzhQSV3qkzLCaU0n5XS+udmvQ2rNQqzaUb9ViH+h0AF3vtn0vtBrtBrNwMafEJWqL1A/MAIWMnrJ6Ww0mZf7Rj9lD8+gKqS0pUhYjFbHaEs5o= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 6/18/26 11:35, Mike Rapoport wrote: > On Thu, Jun 18, 2026 at 11:25:31AM +0200, David Hildenbrand (Arm) wrote: >> On 6/18/26 11:21, Mike Rapoport wrote: >>> >>> 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. My point would be that we exclude all special VMAs, except hugetlb (which is special but supported ... in its special way). -- Cheers, David