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 C2FFDC79F99 for ; Tue, 8 Sep 2026 14:04:15 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists1p.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1x3wQM-00044F-Jg; Tue, 08 Sep 2026 10:03:46 -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 1x3wQJ-00043o-Pn for qemu-devel@nongnu.org; Tue, 08 Sep 2026 10:03:43 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1x3wQH-0006W3-VN for qemu-devel@nongnu.org; Tue, 08 Sep 2026 10:03:43 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1788876220; 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=ALBhOQOvQtfNpwpG6MDrsr5t8tK+bHFFOpNwxHDMX7Y=; b=XpM8gguC0BUWfgSo2sG/06Jvu7fJZyOae2N34fdyeUwbtgdPUAJ5hVIC7ZwzFqslx8TWlr Z0kuAh04NfLYSRwixcPwSojIRmb8Sil8hPQJYudE8sAHifnvJMEd8QtzKhJKNZdmW7UumA hoVzKKkEM8cgZZi4ak+xpRk9EcvQLx8= Received: from mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-442-TZZZya-3MG2Ia0y1t62Ebg-1; Tue, 08 Sep 2026 10:03:35 -0400 X-MC-Unique: TZZZya-3MG2Ia0y1t62Ebg-1 X-Mimecast-MFC-AGG-ID: TZZZya-3MG2Ia0y1t62Ebg_1788876212 Received: from mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.4]) (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-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 99E90195DE4F; Tue, 8 Sep 2026 14:03:31 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.44.22.5]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id B31B330002E9; Tue, 8 Sep 2026 14:03:30 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 67EA621E6A04; Tue, 08 Sep 2026 16:03:28 +0200 (CEST) From: Markus Armbruster To: Michael Roth Cc: , , , , , , , , , Peter Xu , Fabiano Rosas Subject: Re: [PATCH v5 08/12] hostmem: Support fully shared guest memfd to back a VM In-Reply-To: <20260908133151.836685-9-michael.roth@amd.com> (Michael Roth's message of "Tue, 8 Sep 2026 08:30:58 -0500") References: <20260908133151.836685-1-michael.roth@amd.com> <20260908133151.836685-9-michael.roth@amd.com> Date: Tue, 08 Sep 2026 16:03:28 +0200 Message-ID: <87ecf3rgb3.fsf@pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 Received-SPF: pass client-ip=170.10.133.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: 12 X-Spam_score: 1.2 X-Spam_bar: + X-Spam_report: (1.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, 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_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_SBL_CSS=3.335, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=no 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,guest-memfd=on,share=on > > Note that share=on is required with fully shared guest_memfd. > > PS: there's a trivial touch-up on fd<0 check, because the stub to create > guest-memfd may return negative but not -1. > > Signed-off-by: Peter Xu > Reviewed-by: Xiaoyao Li > Reviewed-by: Fabiano Rosas > Signed-off-by: Michael Roth [...] > diff --git a/qapi/qom.json b/qapi/qom.json > index 4a9b7f9088..909add4299 100644 > --- a/qapi/qom.json > +++ b/qapi/qom.json > @@ -771,13 +771,17 @@ > # @seal: if true, create a sealed-file, which will block further > # resizing of the memory (default: true) > # > +# @guest-memfd: if true, use guest-memfd to back the memory region. > +# (default: false, since: 11.2) What's guest-memfd and why would I want to use it? > +# > # Since: 2.12 > ## > { 'struct': 'MemoryBackendMemfdProperties', > 'base': 'MemoryBackendProperties', > 'data': { '*hugetlb': 'bool', > '*hugetlbsize': 'size', > - '*seal': 'bool' }, > + '*seal': 'bool', > + '*guest-memfd': 'bool' }, > 'if': 'CONFIG_LINUX' } > > ##