From nobody Sun Feb 8 17:46:34 2026 Delivered-To: importer@patchew.org Received-SPF: pass (zoho.com: domain of redhat.com designates 209.132.183.24 as permitted sender) client-ip=209.132.183.24; envelope-from=libvir-list-bounces@redhat.com; helo=mx3-phx2.redhat.com; Authentication-Results: mx.zoho.com; spf=pass (zoho.com: domain of redhat.com designates 209.132.183.24 as permitted sender) smtp.mailfrom=libvir-list-bounces@redhat.com; Return-Path: Received: from mx3-phx2.redhat.com (mx3-phx2.redhat.com [209.132.183.24]) by mx.zohomail.com with SMTPS id 1487859601607661.9560598183239; Thu, 23 Feb 2017 06:20:01 -0800 (PST) Received: from lists01.pubmisc.prod.ext.phx2.redhat.com (lists01.pubmisc.prod.ext.phx2.redhat.com [10.5.19.33]) by mx3-phx2.redhat.com (8.13.8/8.13.8) with ESMTP id v1NEGwQS030050; Thu, 23 Feb 2017 09:16:58 -0500 Received: from int-mx13.intmail.prod.int.phx2.redhat.com (int-mx13.intmail.prod.int.phx2.redhat.com [10.5.11.26]) by lists01.pubmisc.prod.ext.phx2.redhat.com (8.13.8/8.13.8) with ESMTP id v1NEFUBP022304 for ; Thu, 23 Feb 2017 09:15:30 -0500 Received: from virval.usersys.redhat.com (dhcp129-92.brq.redhat.com [10.34.129.92]) by int-mx13.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id v1NEFTKO015250 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=NO) for ; Thu, 23 Feb 2017 09:15:30 -0500 Received: by virval.usersys.redhat.com (Postfix, from userid 500) id 63461102389; Thu, 23 Feb 2017 15:15:27 +0100 (CET) From: Jiri Denemark To: libvir-list@redhat.com Date: Thu, 23 Feb 2017 15:15:03 +0100 Message-Id: In-Reply-To: References: In-Reply-To: References: Mail-Followup-To: libvir-list@redhat.com X-Scanned-By: MIMEDefang 2.68 on 10.5.11.26 X-loop: libvir-list@redhat.com Subject: [libvirt] [PATCH v3 05/28] docs: Update description of the host-model CPU mode X-BeenThere: libvir-list@redhat.com X-Mailman-Version: 2.1.12 Precedence: junk List-Id: Development discussions about the libvirt library & tools List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Sender: libvir-list-bounces@redhat.com Errors-To: libvir-list-bounces@redhat.com X-ZohoMail: RSF_0 Z_629925259 SPT_0 Content-Type: text/plain; charset="utf-8" Signed-off-by: Jiri Denemark --- Notes: Version 3: - reworded and updated documentation =20 Version 2: - no change docs/formatdomain.html.in | 37 ++++++++++++++++++++++++------------- 1 file changed, 24 insertions(+), 13 deletions(-) diff --git a/docs/formatdomain.html.in b/docs/formatdomain.html.in index 02ce7924c..ee631186c 100644 --- a/docs/formatdomain.html.in +++ b/docs/formatdomain.html.in @@ -1272,19 +1272,21 @@ model even if the destination host contains more capable CPUs for the running instance of the guest; but shutting down and restart= ing the guest may present different hardware to the guest according = to - the capabilities of the new host. Beware, due t= o the - way libvirt detects host CPU and due to the fact libvirt does not - talk to QEMU/KVM when creating the CPU model, CPU configuration - created using host-model may not work as expected. = The - guest CPU may differ from the configuration and it may also conf= use - guest OS by using a combination of CPU features and other parame= ters - (such as CPUID level) that don't work. Until these issues are fi= xed, - it's a good idea to avoid using host-model and use - custom mode with just the CPU model from host - capabilities XML. - Since 1.2.11 PowerISA allows - processors to run VMs in binary compatibility mode supporting an - older version of ISA. Libvirt on PowerPC architecture uses the + the capabilities of the new host. Prior to libvirt 3.1.0 and QEMU + 2.9.0 detection of the host CPU model via QEMU is not supported. + Thus the CPU configuration created using host-model + may not work as expected. + Since 3.1.0 and QEMU 2.9.0 this mode + works the way it was designed and it is indicated by the + fallback attribute set to forbid in the + host-model CPU definition advertised in + domain capabilitie= s XML. + When fallback attribute is set to allow + in the domain capabilities XML, it is recommended to use + custom mode with just the CPU model from the host + capabilities XML. Since 1.2.11 Powe= rISA + allows processors to run VMs in binary compatibility mode suppor= ting + an older version of ISA. Libvirt on PowerPC architecture uses t= he host-model to signify a guest mode CPU running in binary compatibility mode. Example: When a user needs a power7 VM to run in compatibility mode @@ -1307,6 +1309,15 @@ a migration is attempted then the guest may hang or crash upon resuming execution on the destination host. + + Both host-model and host-passthrough mod= es + make sense when a domain can run directly on the host CPUs (for + example, domains with type kvm). The actual host CPU = is + irrelevant for domains with emulated virtual CPUs (such as domains= with + type qemu). However, for backward compatibility + host-model may be implemented even for domains runnin= g on + emulated CPUs in which case the best CPU the hypervisor is able to + emulate may be used rather then trying to mimic the host CPU model. =20
model
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