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Wed, 19 Nov 2025 17:35:47 +0000 (UTC) X-Farcaster-Flow-ID: de87be56-055f-4e2c-857c-09a3093658e3 Received: from EX19D022EUC002.ant.amazon.com (10.252.51.137) 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; Wed, 19 Nov 2025 17:35:37 +0000 Received: from [192.168.8.246] (10.106.82.8) by EX19D022EUC002.ant.amazon.com (10.252.51.137) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.2.2562.29; Wed, 19 Nov 2025 17:35:36 +0000 Message-ID: Date: Wed, 19 Nov 2025 17:35:32 +0000 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Reply-To: Subject: Re: [RFC PATCH 0/4] mm, kvm: add guest_memfd support for uffd minor faults To: Peter Xu CC: Mike Rapoport , , Andrea Arcangeli , Andrew Morton , Baolin Wang , David Hildenbrand , "Hugh Dickins" , "Liam R. Howlett" , Lorenzo Stoakes , Michal Hocko , Paolo Bonzini , Sean Christopherson , Shuah Khan , Suren Baghdasaryan , Vlastimil Babka , , , References: <20251117114631.2029447-1-rppt@kernel.org> 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: [10.106.82.8] X-ClientProxiedBy: EX19D010EUA003.ant.amazon.com (10.252.50.136) To EX19D022EUC002.ant.amazon.com (10.252.51.137) X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 58C53100004 X-Stat-Signature: 7k59jwco8xyh3qhxzmrpw9jyueymfwtr X-Rspam-User: X-HE-Tag: 1763573767-299680 X-HE-Meta: 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 ISsgj+7b 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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 17/11/2025 19:39, Peter Xu wrote: > On Mon, Nov 17, 2025 at 05:55:46PM +0000, Nikita Kalyazin wrote: >> In our use case, Firecracker snapshot-restore using UFFD [1], we will use >> UFFD minor/continue to respond to guest_memfd faults in user mappings >> primarily due to VMM accesses that are required for PV (virtio) device >> emulation and also KVM accesses when decoding MMIO operations on x86. > > I'm curious if firecracker plans to support live snapshot save. When with > something like ioctls_supported flags, guest-memfd can declare support for > wr-protect support easily too, and synchronous userfaultfd wr-protect traps > will be an efficient way to do live save. > > I'm guessing it's not an immediate demand now or it would have been asked > already supporting both MINOR and WP, but I just want to raise this > question. Qemu already supports live snapshot save, so it'll always be > good gmem can also support wp at some point, but it can be done later too. No, live snapshots haven't been on our plan so far. > > Thanks, > > -- > Peter Xu >