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Fri, 28 Nov 2025 12:15:54 +0000 (UTC) X-Farcaster-Flow-ID: 0de054ca-fa8f-4660-b374-417544b79f00 Received: from EX19D005EUB003.ant.amazon.com (10.252.51.31) by EX19MTAEUC001.ant.amazon.com (10.252.51.155) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.2.2562.29; Fri, 28 Nov 2025 12:15:54 +0000 Received: from [192.168.12.95] (10.106.83.26) by EX19D005EUB003.ant.amazon.com (10.252.51.31) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.2.2562.29; Fri, 28 Nov 2025 12:15:52 +0000 Message-ID: <4405c306-9d7c-4fd6-9ea6-2ed1b73f5c2e@amazon.com> Date: Fri, 28 Nov 2025 12:15:51 +0000 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Reply-To: Subject: Re: [PATCH v2 4/5] guest_memfd: add support for userfaultfd minor mode To: Mike Rapoport CC: , Andrea Arcangeli , "Andrew Morton" , Axel Rasmussen , Baolin Wang , David Hildenbrand , Hugh Dickins , "James Houghton" , "Liam R. Howlett" , Lorenzo Stoakes , Michal Hocko , Paolo Bonzini , Peter Xu , Sean Christopherson , Shuah Khan , Suren Baghdasaryan , Vlastimil Babka , , , References: <20251125183840.2368510-1-rppt@kernel.org> <20251125183840.2368510-5-rppt@kernel.org> <13d3a7a4-5cf8-4fbe-8dba-d565525a71c6@amazon.com> Content-Language: en-US From: Nikita Kalyazin Autocrypt: addr=kalyazin@amazon.com; keydata= xjMEY+ZIvRYJKwYBBAHaRw8BAQdA9FwYskD/5BFmiiTgktstviS9svHeszG2JfIkUqjxf+/N JU5pa2l0YSBLYWx5YXppbiA8a2FseWF6aW5AYW1hem9uLmNvbT7CjwQTFggANxYhBGhhGDEy BjLQwD9FsK+SyiCpmmTzBQJnrNfABQkFps9DAhsDBAsJCAcFFQgJCgsFFgIDAQAACgkQr5LK IKmaZPOpfgD/exazh4C2Z8fNEz54YLJ6tuFEgQrVQPX6nQ/PfQi2+dwBAMGTpZcj9Z9NvSe1 CmmKYnYjhzGxzjBs8itSUvWIcMsFzjgEY+ZIvRIKKwYBBAGXVQEFAQEHQCqd7/nb2tb36vZt ubg1iBLCSDctMlKHsQTp7wCnEc4RAwEIB8J+BBgWCAAmFiEEaGEYMTIGMtDAP0Wwr5LKIKma ZPMFAmes18AFCQWmz0MCGwwACgkQr5LKIKmaZPNTlQEA+q+rGFn7273rOAg+rxPty0M8lJbT i2kGo8RmPPLu650A/1kWgz1AnenQUYzTAFnZrKSsXAw5WoHaDLBz9kiO5pAK In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.106.83.26] X-ClientProxiedBy: EX19D014EUA003.ant.amazon.com (10.252.50.119) To EX19D005EUB003.ant.amazon.com (10.252.51.31) X-Rspamd-Queue-Id: 7565C120006 X-Rspamd-Server: rspam06 X-Rspam-User: X-Stat-Signature: 5ymg4ekuy8frjku34mjjy5gb9mtery39 X-HE-Tag: 1764332171-67882 X-HE-Meta: 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 7ykZHT/k 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 27/11/2025 19:04, Mike Rapoport wrote: > On Thu, Nov 27, 2025 at 11:19:35AM +0000, Nikita Kalyazin wrote: >> >> >> On 27/11/2025 10:36, Mike Rapoport wrote: >>> On Wed, Nov 26, 2025 at 04:49:31PM +0000, Nikita Kalyazin wrote: >>>> On 25/11/2025 18:38, Mike Rapoport wrote: >>>>> From: "Mike Rapoport (Microsoft)" >>>>> >>>>> +#ifdef CONFIG_USERFAULTFD >>>>> +static struct folio *kvm_gmem_get_folio(struct inode *inode, pgoff_t pgoff) >>>> >>>> We have to name it differently, otherwise it clashes with the existing one >>>> in this file. >>> >>> It's all David's fault! ;-P >>> How about kvm_gmem_get_prepared_folio() ? >> >> I'm afraid it may not be ideal due to preparedness tracking being removed >> from guest_memfd at some point [1]. Would it be too bad to add an >> indication to userfaultfd in the name somehow given that it's already >> guarded by the config? > > Hmm, shmem also has this clash. There I picked shmem_get_folio_noalloc() > because that describes well what it does: lookup folio in the page cache, > grab it if it's there or return -ENOENT if it's missing. > That's also what hugetlb does for uffd minor fault. > > The guest_memfd implementation I copied from one of the older postings > allocates the folio if it's not in the page cache and it seems to me that > it also should only look up existing folios to keep uffd minor semantics > uniform. I can't see a reason for guest_memfd to deviate from shmem and hugetlb here so makes sense to me. > > Then it makes sense also to name the vm_ops method get_folio_noalloc(). > > -- > Sincerely yours, > Mike.