From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 0FB8B3E8C74; Wed, 17 Jun 2026 10:34:47 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781692492; cv=none; b=oz+vahQfmDfWXppks+UB/jtgQbgHszqEUXrlhDjneavsg76WOefUakyNINoJqfINwNURHe3zMi4MyQHQz3xENZ2XH7L8Kedo14tcRE/gtnHo4jYyaeg0WWIhDvZQuMfjacPpM6ERyvlS9tOIuckXEEXgUA008tEX8ie5DW7X6wg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781692492; c=relaxed/simple; bh=rOXBbFduSVEhk7vn/B/fnnV9GpMne8ukQbUrDuDuwb8=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=kW6MIlaC1KtIXWjuSwBixgP4pJj3ZMMpRygTJsQGHm5oze4Kb4wWR/TWzzRxwHyH+oD1x01l92Dgf4jq+Ga7gDXbOC82WUx8sHeUPZP3cqlE/JoHDUiHu5VESaxhN3cnI4XBhG56nNQHCmg8Gz7D2cuRGXtD4scmk2tKqwQEeKM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Wv97yqYT; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Wv97yqYT" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 38FC81F000E9; Wed, 17 Jun 2026 10:34:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1781692487; bh=mUzimGhtwXxeFlNbjp2T5cpsz2AsOPIbGLnMGM1e6Dk=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=Wv97yqYTUmHJUFnZj5sV6+KfbOH9WCS97aAe2ipipFgYFnAgIyBaKA0DCVPWhme8b jBXKmFR2LjzO+WhSOm9S4yVMbmlCGSH11yqqO0mq9Xr+BMQwf85wyzev4hqlx7sAUT TP75DRBIfR2q7apcjUstwzSBStuIhrXIKy0StOYafxpFp1VHhyvgwcppG1/+ui/4da DESJJGo+QdHVu+ZYi2jSI9lSUgtYxh3qp8sgvNI53EqqofZTgpeK2jKBhZFfFk8Wf3 TqJyGELBLbKO32SIHiP5JHb5yBTFjIcK1lUfKpyDqSi0Ae97MquHzGkCTY7bgu/xsK W2A4DwTyVd02g== Message-ID: <9ebadac0-0ec2-4ebc-8193-1a289574c0a9@kernel.org> Date: Wed, 17 Jun 2026 12:34:38 +0200 Precedence: bulk X-Mailing-List: linux-coco@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH RFC 0/3] KVM: guest_memfd: folio migration for non-confidential VMs To: Ackerley Tng , Sean Christopherson , Alexandru Elisei Cc: Shivank Garg , "Matthew Wilcox (Oracle)" , Jan Kara , Andrew Morton , Vlastimil Babka , Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Johannes Weiner , Zi Yan , Matthew Brost , Joshua Hahn , Rakie Kim , Byungchul Park , Gregory Price , Ying Huang , Alistair Popple , Paolo Bonzini , Shuah Khan , Chao Peng , Nikunj A Dadhania , Ira Weiny , Michael Roth , Pankaj Gupta , Fuad Tabba , Vishal Annapurve , Nikita Kalyazin , Patrick Roy , Pratik Sampat , Ashish Kalra , linux-fsdevel@vger.kernel.org, linux-coco@lists.linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, linux-kselftest@vger.kernel.org References: <20260611-shivank-gmem-migrate-v1-0-2d266bfc6f95@amd.com> <1e77f24d-315a-4f68-a109-2f4520343c0c@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 On 6/16/26 20:09, Ackerley Tng wrote: > "David Hildenbrand (Arm)" writes: > >> On 6/15/26 19:39, Sean Christopherson wrote: >>> >>> +1000. It's not just "nice to have", it's a core design principle of guest_memfd. >> >> Right, and I raised in the guest_memfd call also the rough idea of Alexandru's >> use case of having non-movable guest_memfd pages such that we can support use >> cases where we can hopefully guarantee that a stage-2 mapping will not just >> randomly go away. >> >>> > > More concretely, are y'all pointing towards a > GUEST_MEMFD_FLAG_MIGRATABLE, which will set .migrate = > kvm_gmem_migrate_folio, and for now, error out for CoCo VMs? > >>> >>> For the purposes of this discussion, we should separate the physical act of >>> migrating pages from the features that trigger migration. As I said in last week's >>> guest-memfd call, I am a-ok with supporting page migration as a mechanism, but I >>> am dead set against supporting NUMA balancing, KSM, LRU-based swap/reclaim, and >>> anything else that goes against the goal of guest-first memory. >> >> Right. Page migration for supporting ZONE_MOVABLE/CMA, compaction, memory >> offlining, virtio-mem and possibly some collapse mechanism if we were to support >> THP of some sorts in guest_memfd would are all reasonable. >> > > Background question: how would virtio-mem use migration in the host/guest_memfd? Good question! As long as there is no nested-virt support (and virtio-mem support for coco still being in the making) that wouldn't apply, only ordinary memory hot(un)plug (incl CXL). -- Cheers, David