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 lists.gnu.org (lists.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 C6226E7716C for ; Thu, 5 Dec 2024 08:26:03 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1tJ7B9-0001vP-NW; Thu, 05 Dec 2024 03:25:43 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1tJ7B7-0001ut-GU for qemu-devel@nongnu.org; Thu, 05 Dec 2024 03:25:41 -0500 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 1tJ7B5-0007Ef-Su for qemu-devel@nongnu.org; Thu, 05 Dec 2024 03:25:41 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1733387137; 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=e1xn8iZBaLbuNsrD9/fBIbkbW/LFhfvi+btN/FRdYZ8=; b=Ntb5C6ny0aDyerokuTQPEjFJvcd1V9XtePC027GnI60ymvTX39E8MvdqEEi0VXHr98XU76 MJjVyzJV7vOoVDEi5nz6ptIQjxoSU5jTzXpZ1MW9e4T80Kjy1BnZ2esRYQSj+FLac7sncD ut44OPjeyMsX5+BuF+q6P4zQn7nGGs4= Received: from mx-prod-mc-04.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-396-0SECbkCYM9a7NAOCD4BiIA-1; Thu, 05 Dec 2024 03:25:33 -0500 X-MC-Unique: 0SECbkCYM9a7NAOCD4BiIA-1 X-Mimecast-MFC-AGG-ID: 0SECbkCYM9a7NAOCD4BiIA Received: from mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.40]) (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-04.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 1AE2019560B3; Thu, 5 Dec 2024 08:25:32 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.39.194.102]) by mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id E431C1956054; Thu, 5 Dec 2024 08:25:29 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 96C3D21E66CD; Thu, 5 Dec 2024 09:25:27 +0100 (CET) From: Markus Armbruster To: Steve Sistare Cc: qemu-devel@nongnu.org, Peter Xu , Fabiano Rosas , David Hildenbrand , Marcel Apfelbaum , Eduardo Habkost , Philippe Mathieu-Daude , Paolo Bonzini , "Daniel P. Berrange" Subject: Re: [PATCH V4 04/19] machine: aux-ram-share option In-Reply-To: <1733145611-62315-5-git-send-email-steven.sistare@oracle.com> (Steve Sistare's message of "Mon, 2 Dec 2024 05:19:56 -0800") References: <1733145611-62315-1-git-send-email-steven.sistare@oracle.com> <1733145611-62315-5-git-send-email-steven.sistare@oracle.com> Date: Thu, 05 Dec 2024 09:25:27 +0100 Message-ID: <87ikryh6yw.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 10.30.177.40 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: -50 X-Spam_score: -5.1 X-Spam_bar: ----- X-Spam_report: (-5.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-2.999, 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, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001, SPF_HELO_NONE=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: 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 Steve Sistare writes: > Allocate auxilliary guest RAM as an anonymous file that is shareable > with an external process. This option applies to memory allocated as > a side effect of creating various devices. It does not apply to > memory-backend-objects, whether explicitly specified on the command > line, or implicitly created by the -m command line option. > > This option is intended to support new migration modes, in which the > memory region can be transferred in place to a new QEMU process, by sending > the memfd file descriptor to the process. Memory contents are preserved, > and if the mode also transfers device descriptors, then pages that are > locked in memory for DMA remain locked. This behavior is a pre-requisite > for supporting vfio, vdpa, and iommufd devices with the new modes. > > Signed-off-by: Steve Sistare [...] > diff --git a/qemu-options.hx b/qemu-options.hx > index dacc979..02b9118 100644 > --- a/qemu-options.hx > +++ b/qemu-options.hx > @@ -38,6 +38,9 @@ DEF("machine", HAS_ARG, QEMU_OPTION_machine, \ > " nvdimm=on|off controls NVDIMM support (default=off)\n" > " memory-encryption=@var{} memory encryption object to use (default=none)\n" > " hmat=on|off controls ACPI HMAT support (default=off)\n" > +#ifdef CONFIG_POSIX > + " aux-ram-share=on|off allocate auxiliary guest RAM as shared (default: off)\n" > +#endif > " memory-backend='backend-id' specifies explicitly provided backend for main RAM (default=none)\n" > " cxl-fmw.0.targets.0=firsttarget,cxl-fmw.0.targets.1=secondtarget,cxl-fmw.0.size=size[,cxl-fmw.0.interleave-granularity=granularity]\n", > QEMU_ARCH_ALL) > @@ -101,6 +104,18 @@ SRST > Enables or disables ACPI Heterogeneous Memory Attribute Table > (HMAT) support. The default is off. > > +#ifdef CONFIG_POSIX > + ``aux-ram-share=on|off`` > + Allocate auxiliary guest RAM as an anonymous file that is > + shareable with an external process. This option applies to > + memory allocated as a side effect of creating various devices. > + It does not apply to memory-backend-objects, whether explicitly > + specified on the command line, or implicitly created by the -m > + command line option. > + > + Some migration modes require aux-ram-share=on. This leaves the one thing users really need to know unsaid: when exactly should users enable it. "Some migration modes require aux-ram-share=on": do they enable it by default, or is that left to the user? If the latter, why? Please document the default, whatever it is. > +#endif > + > ``memory-backend='id'`` > An alternative to legacy ``-mem-path`` and ``mem-prealloc`` options. > Allows to use a memory backend as main RAM. [...]