From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 4078FCD98C7 for ; Mon, 15 Jun 2026 11:04:31 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id A387A6B0005; Mon, 15 Jun 2026 07:04:30 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 9C1776B008A; Mon, 15 Jun 2026 07:04:30 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 8891A6B008C; Mon, 15 Jun 2026 07:04:30 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id 715246B0005 for ; Mon, 15 Jun 2026 07:04:30 -0400 (EDT) Received: from smtpin03.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay04.hostedemail.com (Postfix) with ESMTP id 0E5C31A0984 for ; Mon, 15 Jun 2026 11:04:30 +0000 (UTC) X-FDA: 84881863500.03.808812B Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by imf11.hostedemail.com (Postfix) with ESMTP id F1A5E40006 for ; Mon, 15 Jun 2026 11:04:27 +0000 (UTC) Authentication-Results: imf11.hostedemail.com; dkim=pass header.d=arm.com header.s=foss header.b=ITcrxen1; dmarc=pass (policy=none) header.from=arm.com; spf=pass (imf11.hostedemail.com: domain of alexandru.elisei@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=alexandru.elisei@arm.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1781521468; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=9hWOY7MWUjRw7SnwfLftxff6I6ZGrfupK3fRU9X3Vrg=; b=Olbo8uSH1pixTKyamP4C8E6rUqCqIGwQq7VPXsUTc9LNgNAVdeJdxu9QBQHi3/95PtlW0b +nKpeXHRKhPStH/j+L/v+3x7yWsZhpITE9WT2FJ1upWTrFEwcqk2bf9qBcZc8lEw/0V2KM 3/aYIvhl0fjRpl4zi/9IhxwTYNqC6WY= ARC-Authentication-Results: i=1; imf11.hostedemail.com; dkim=pass header.d=arm.com header.s=foss header.b=ITcrxen1; dmarc=pass (policy=none) header.from=arm.com; spf=pass (imf11.hostedemail.com: domain of alexandru.elisei@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=alexandru.elisei@arm.com ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1781521468; b=fgBYk586Wh2Uv4txfkyIdn25vMU6St06YijeyRS2y7BnuW8TCDEELFBG9ayFDQpWYWqa4i dbnv81KrkuAC1FsBrovg47dKR+By6MgzATPgRLusPSdV7UfC8CQnKb1XhNVFz5SCcUITDf zMZON2lpi7JrwI2bvi6DLl9TwtV+8D0= Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 4303E328D; Mon, 15 Jun 2026 04:04:22 -0700 (PDT) Received: from raptor (usa-sjc-mx-foss1.foss.arm.com [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id E54C13F915; Mon, 15 Jun 2026 04:04:21 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1781521467; bh=G5bCUMpAj7XkCblIAeX+67lQJO0pVJ0HsMawKtJgxQU=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=ITcrxen1FUILXt0yTvFGlM97RCokdSUG6KreIW5VnfKj1yUsv5nAXAUCQjVOZEyus 1bxtVRPtXhyGGGbSLmKSdOfzkBrck+oXlbdN9jdKXe1uibx4w6l3zzqX0H/xXyhSXE z3BP5/FQv9K7Ctbm7B/qLe39ZaH6N64JsRAQb/a8= Date: Mon, 15 Jun 2026 12:04:15 +0100 From: Alexandru Elisei To: Shivank Garg Cc: "Matthew Wilcox (Oracle)" , Jan Kara , Andrew Morton , Vlastimil Babka , Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Johannes Weiner , Zi Yan , David Hildenbrand , 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 , Ackerley Tng , Fuad Tabba , Sean Christopherson , 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 Subject: Re: [PATCH RFC 0/3] KVM: guest_memfd: folio migration for non-confidential VMs Message-ID: References: <20260611-shivank-gmem-migrate-v1-0-2d266bfc6f95@amd.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: F1A5E40006 X-Rspam-User: X-Stat-Signature: f6ii5bds1rhg8rir9mhh41fpz1b5d9fj X-Rspamd-Server: rspam09 X-HE-Tag: 1781521467-312008 X-HE-Meta: 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 r0Dj9U74 c+OPGwHSn7QS8Q0Xm831nrKfp8lIaKxizI0GVeDfh+/Oxj+2k7eenWBNZA6qwFP4xQ/+oL0Fu7qRU/IjCQ89zBfZku1MGN6dJw7iHC2LYK+8onQByGkawgRPgsqE4PqHvg4bow9zoIyOMCS1iR7U1R9Y0InMH3m8woggoMnDIYRF7ifPwRvnti66c4t0aQIn9GZ+/KvDfIC3s8sILXFeeQPoDWphXIN2BSD5+OVAgy6JFFJtJl6c7NZpMhnVFOe5ygH92jMXU+Wyhf5DoNyyEFirGZeYtfkW4iC4d4qPYGsF4NyRWBhj74v1HMZWyl2Tf+cGSzCHHQ8HjYfzg5va4a/9D2+2K72HSwRmm Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi, On Mon, Jun 15, 2026 at 11:43:14AM +0100, Alexandru Elisei wrote: > Hi, > > On Thu, Jun 11, 2026 at 01:05:07PM +0000, Shivank Garg wrote: > > guest_memfd folios are currently marked unmovable, so the kernel cannot > > perform NUMA-balancing, memory compaction, etc. This is unavoidable for > > confidential VMs (SEV-SNP, TDX), since memory is encrypted and copying it > > needs firmware assistance. However, for non-confidential VMs (like > > Firecracker), we can migrate the folios. > > > > This series enables folio migration for non-confidential guest_memfd and > > also lays the groundwork for migrating confidential guest_memfd later. > > Once firmware-assisted copying support is available, those VMs can be > > made movable, the confidential folio content can be copied separately, > > and the destination folio marked with FOLIO_CONTENT_COPIED so > > __migrate_folio() skips the host-side folio_mc_copy(). > > I always thought that one of the nice things about using guest_memfd as a > memory backend, as opposed to host userspace mappings, is that the host > cannot unmap VM memory because of KSM, automatic NUMA balancing, hugepage > collapse, compaction, etc, acting on the host userspace mapping of the > VM memory, and outside of the VMM's or KVM's control. > > I think it would be useful to preserve this behaviour, even in the absence > of confidential VMs (i.e, guest_memfd file descriptor created with > GUEST_MEMFD_FLAG_MMAP). Just to be clear, I was thinking that it might be useful for both behaviours to exist (migratable and non-migratable) for non-confidential VMs, and allow KVM or userspace to decide which they prefer for a guest_memfd. Thanks, Alex