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Tue, 23 Sep 2025 12:13:57 +0000 (UTC) X-Farcaster-Flow-ID: 8181f46e-0526-4b06-9460-3a2e1a03356b Received: from EX19D022EUC002.ant.amazon.com (10.252.51.137) by EX19MTAEUA002.ant.amazon.com (10.252.50.124) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.2.2562.20; Tue, 23 Sep 2025 12:13:54 +0000 Received: from [192.168.26.206] (10.106.82.20) 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 15.2.2562.20; Tue, 23 Sep 2025 12:13:53 +0000 Message-ID: <8408090a-d2cc-4b90-99fe-183d49081ea4@amazon.com> Date: Tue, 23 Sep 2025 13:13:51 +0100 Precedence: bulk X-Mailing-List: kvmarm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Reply-To: Subject: Re: [PATCH v3 00/15] KVM: Introduce KVM Userfault To: Sean Christopherson , James Houghton CC: Paolo Bonzini , Oliver Upton , Jonathan Corbet , Marc Zyngier , Yan Zhao , Anish Moorthy , Peter Gonda , Peter Xu , David Matlack , , , , , , References: <20250618042424.330664-1-jthoughton@google.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: 8bit X-ClientProxiedBy: EX19D015EUA002.ant.amazon.com (10.252.50.219) To EX19D022EUC002.ant.amazon.com (10.252.51.137) On 05/09/2025 13:27, Sean Christopherson wrote: > On Thu, Sep 04, 2025, James Houghton wrote: >> On Thu, Sep 4, 2025 at 9:43 AM Nikita Kalyazin wrote: >>> Are there any blockers for merging this series? We would like to use >>> the functionality in Firecracker for restoring guest_memfd-backed VMs >>> from snapshots via UFFD [1]. [2] is a Firecracker feature branch that >>> builds on top of KVM userfault, along with direct map removal [3], write >>> syscall [4] and UFFD support [5] in guest_memfd (currently in discussion >>> with MM at [6]) series. >> >> Glad to hear that you need this series. :) > > Likewise (though I had slightly-advanced warning from Patrick that Firecracker > wants KVM Userfault). The main reason I haven't pushed harder on this series is > that I didn't think anyone wanted to use it within the next ~year. > >> I am on the hook to get some QEMU patches to demonstrate that KVM >> Userfault can work well with it. I'll try to get that done ASAP now >> that you've expressed interest. The firecracker patches are a nice >> demonstration that this could work too... (I wish the VMM I work on >> was open-source). >> >> I think the current "blocker" is the kvm_page_fault stuff[*]; KVM >> Userfault will be the first user of this API. I'll review that series >> in the next few days. I'm pretty sure Sean doesn't have any conceptual >> issues with KVM Userfault as implemented in this series. > > Yep, Oliver and I (and anyone else that has an opinion) just need to align on the > interface for arch-neutral code. I think that's mostly on me to spin a v2, and > maybe to show how it all looks when integrated with the userfault stuff.\ Sounds good, thanks. Do you think you'll be having time to work on the v2 soonish? Is defining and implementing the interface a strict prerequisite for this series?