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 lists1p.gnu.org (lists1p.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 4B670C9830E for ; Wed, 30 Sep 2026 05:14:48 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists1p.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1xBmdl-0001Vn-Hl; Wed, 30 Sep 2026 01:14:01 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists1p.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1xBmdk-0001Vd-4s for qemu-devel@nongnu.org; Wed, 30 Sep 2026 01:14:00 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1xBmdi-0005zr-9E for qemu-devel@nongnu.org; Wed, 30 Sep 2026 01:13:59 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1790745236; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=O5BjoZ6/godBeTMa09s67ekRBYqqIQyjumOndzJr+tI=; b=ayvciFtUjlc7NJRh16AfTc3FrsQVKbSC9ZFUP0rrMMAA7v5zf8NeH3wi6t9XlFoQo6mOWd /8DxHAQt9Vo/XpUu/SZYgU0eJDiPHGbuImwTpQsSQm8bNQqULM+RwLaZbIPTvbzpEbfeUW CagVTgQComP48x49/3rmZ3v1u6QxG0s= Received: from mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-365-eYHtrYntO8Wi-We_tpUQQw-1; Wed, 30 Sep 2026 01:13:53 -0400 X-MC-Unique: eYHtrYntO8Wi-We_tpUQQw-1 X-Mimecast-MFC-AGG-ID: eYHtrYntO8Wi-We_tpUQQw_1790745231 Received: from mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.17]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 60A121800A7F; Wed, 30 Sep 2026 05:13:51 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.44.22.5]) by mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 6CD1F19560AB; Wed, 30 Sep 2026 05:13:50 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 0839821E6A04; Wed, 30 Sep 2026 07:13:48 +0200 (CEST) From: Markus Armbruster To: Michael Roth Cc: , , , , , , , Peter Xu , Fabiano Rosas Subject: Re: [PATCH v7 10/12] hostmem: Support fully shared guest memfd to back a VM In-Reply-To: <20260929235109.1398509-11-michael.roth@amd.com> (Michael Roth's message of "Tue, 29 Sep 2026 18:50:16 -0500") References: <20260929235109.1398509-1-michael.roth@amd.com> <20260929235109.1398509-11-michael.roth@amd.com> Date: Wed, 30 Sep 2026 07:13:48 +0200 Message-ID: <87qzibtj77.fsf@pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 3.0 on 10.30.177.17 Received-SPF: pass client-ip=170.10.129.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -23 X-Spam_score: -2.4 X-Spam_bar: -- X-Spam_report: (-2.4 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.341, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: qemu development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Michael Roth writes: > From: Peter Xu > > Host backends supports guest-memfd now by detecting whether it's a > confidential VM. There's no way to choose it yet from the memory level to > use it fully shared. If we use guest-memfd, it so far always implies we > need two layers of memory backends, while the guest-memfd only provides the > private set of pages. > > This patch introduces a way so that QEMU can consume guest memfd as the > only source of memory to back the object (aka, fully shared). > > To use the fully shared guest-memfd, one can add a memfd object with: > > -object memory-backend-memfd,x-guest-memfd=on,share=on > > Note that share=on is required with fully shared guest_memfd. > > Since guest-memfd is not yet a drop-in replacement for memfd (e.g. lack > of hugepage support), the option is tagged as experimental for now so > that it can be made available for early enablement/testing without > causing any surprises for other users. > > PS: there's a trivial touch-up on fd<0 check, because the stub to create > guest-memfd may return negative but not -1. > > Reviewed-by: Xiaoyao Li > Reviewed-by: Fabiano Rosas > Reviewed-by: David Hildenbrand > Signed-off-by: Peter Xu > [mdr: add accompanying guest-memfd doc, mark as experimental] > Co-developed-by: Michael Roth > Signed-off-by: Michael Roth QAPI schema Acked-by: Markus Armbruster