From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from fra-out-010.esa.eu-central-1.outbound.mail-perimeter.amazon.com (fra-out-010.esa.eu-central-1.outbound.mail-perimeter.amazon.com [63.178.143.178]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 955F130DD13; Wed, 19 Nov 2025 17:36:06 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=63.178.143.178 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1763573769; cv=none; b=U6OOiRlUk3/iISlxPeq2ITW1x9vs5aLqGSWYlI9qhOw2rB3yoMbXnbn2Bp+bKvXSELlrCdd1EErwYU7+nRmXpBja3At3dUewrSQub0BQaTrLKozYW6+mQTJ3NKsYbPYRANfJQxMArFAV5OAiqpxMfY9szTadEUOOe+ENP+okc8c= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1763573769; c=relaxed/simple; bh=KGA1t4uHCezs8UbJHd1OQZZe/6N2sEm6BHNaPJNkI90=; h=Message-ID:Date:MIME-Version:Subject:To:CC:References:From: In-Reply-To:Content-Type; b=HVGoFSufMmE6/aMra1Y069JquAsAI/2yec2ar+KIhtoTbh8cCR085/KXxvLgkoQ3Ztty75PvQOfofFc1bTH/g/+KpobvkJHC1a66srod4L++CGCHIehrcUoyFWL5hSzlE2fO7gyoLn0xylxyE6tQmOGzofnRhzS1F8Uk710qrBU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=amazon.com; spf=pass smtp.mailfrom=amazon.co.uk; dkim=pass (2048-bit key) header.d=amazon.com header.i=@amazon.com header.b=kKguyMYu; arc=none smtp.client-ip=63.178.143.178 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=amazon.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=amazon.co.uk Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=amazon.com header.i=@amazon.com header.b="kKguyMYu" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amazon.com; i=@amazon.com; q=dns/txt; s=amazoncorp2; t=1763573767; x=1795109767; h=message-id:date:mime-version:reply-to:subject:to:cc: references:from:in-reply-to:content-transfer-encoding; bh=MYyWWExzLhYCC4+Jo3opQw3FoaDIdSA/mKXXs7/p6Qo=; b=kKguyMYuPAyLAqhYtK8oQmt3CVpaOTqe+ghuUAMiiMSKSJd5alnd2X5Z eXFiLFolz5Q3rGu16zswnc1oMnuiu0jcrI/nMa0vpt6QCIsvkF1lUf6LV wNPoVDFfKIuLuwKAc5KhGfPheQa9eZR9yq68o+u/69vkirWWTrQ01vVwJ 5zhbJwOhyvZC33ZrIQ5HfVAsPCCV2iwrMJtt2JytMCYSd/DOSuxvPAhwl JWiBKUCfQJzUCuph6hcpAJHn6g/5PvMZNeoFrcgj5wWPimy7KOiAtJhAn lSyXVX0+mj4Wu/t4K8LzQjdF41ESvloSYMBi8tb09OLxPi/TTsMmkBfZM A==; X-CSE-ConnectionGUID: 2KODmyCIQDO7OmZJiRekMg== X-CSE-MsgGUID: /R+RMYiNR2O9nKeRZ0LSfg== X-IronPort-AV: E=Sophos;i="6.19,315,1754956800"; d="scan'208";a="5358484" Received: from ip-10-6-11-83.eu-central-1.compute.internal (HELO smtpout.naws.eu-central-1.prod.farcaster.email.amazon.dev) ([10.6.11.83]) by internal-fra-out-010.esa.eu-central-1.outbound.mail-perimeter.amazon.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 19 Nov 2025 17:35:47 +0000 Received: from EX19MTAEUC001.ant.amazon.com [54.240.197.225:18787] by smtpin.naws.eu-central-1.prod.farcaster.email.amazon.dev [10.0.7.216:2525] with esmtp (Farcaster) id de87be56-055f-4e2c-857c-09a3093658e3; 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 Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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-ClientProxiedBy: EX19D010EUA003.ant.amazon.com (10.252.50.136) To EX19D022EUC002.ant.amazon.com (10.252.51.137) 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 >