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t=1781772444; bh=CnSbWReKGTEDPoaUR3qOev0pPCPHLKT28K++dObk2Z4=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=h2napG4FfR/yPntLk9yltjsnQ1tWjH6S5xgCqt9ov3q4oh5HWT9ILBcDj7n1lAKVS Gj3t0fhK8jL2HzUkqIXxVlJbp7Q5H9PYweet2l1FOjxfJbUE2mxdD6LdxTFYu4NXX6 3CH15FT9GJjMwegnFDDQjy+m3iw6Rs8AOxyjn4JNe7iiTFhUFaqhdtczAn5CB0620e pPSshravIhP7l0D5iSUrj5wwSnIgZqaQcL5XFFzakD5gK2RaVO0MDia0Ibp/yuCtpK OiMWdYA+VXlVBcibkICEFagANR9A52Ue+h6FmWNDLBk3aB/c7ddKRObfDVSlZw25Qc 8ZdFnDLdc/bFg== Message-ID: <41ef0dce-e973-4947-b5e3-150fdb07f1a6@kernel.org> Date: Thu, 18 Jun 2026 10:47:19 +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> 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: rspam11 X-Rspamd-Queue-Id: AEA5B4000B X-Rspam-User: X-Stat-Signature: aonpzfk15yah4pufb164t3gpc76me1w7 X-HE-Tag: 1781772445-731789 X-HE-Meta: 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 dbWWwvH3 WFVpJsKv0EVO+McXg6tarTqifgcIQ3Vatm4xZWo6m1tduQBZr/dhNXOtP+5LLAKSH4iT3qHfEmg9+PDmQ8oMccJJqzbnmfFUk34syMKLZfntrL0rVrB6h5oZyirH1F1lB0XeEnZnwVwVqgmv9AIMneEXeOhhCXeOcCjyFyP3WPaalM7itamVFML6UV8NfTFPR+mHkCAyNKjjKVuBbxWQMJNrUHzsVRBYDJ2YUORVr9O7ZiZkOgTdK7VbGfyY/0dyOAjFj Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 6/18/26 10:43, Mike Rapoport wrote: > On Thu, Jun 18, 2026 at 11:34:12AM +0300, Mike Rapoport wrote: >> On Thu, Jun 18, 2026 at 10:19:17AM +0200, David Hildenbrand (Arm) wrote: >>> >>> I'm sure you considered VM_SPECIAL, which additionally includes VM_DONTEXPAND. >>> >>> Would that be better, or what was the reason to allow VM_DONTEXPAND? >> >> By itself VM_DONTEXPAND won't matter, as uffd can't resize a VMA. >> But thinking more about it, it's better to make vma_can_userfault() more >> restrictive and just use VM_SPECIAL. > > 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. -- Cheers, David