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([2001:b07:6468:f312:dc24:9a59:da87:5724]) by smtp.gmail.com with ESMTPSA id 189sm541664wme.28.2019.11.20.12.49.35 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 20 Nov 2019 12:49:36 -0800 (PST) Subject: Re: [PATCH] target/i386: add VMX features to named CPU models To: Eduardo Habkost References: <20191120173753.8894-1-pbonzini@redhat.com> <20191120184533.GT3812@habkost.net> From: Paolo Bonzini Openpgp: preference=signencrypt Message-ID: Date: Wed, 20 Nov 2019 21:49:35 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20191120184533.GT3812@habkost.net> Content-Language: en-US X-MC-Unique: 0zxg52C3OmWyCVtJjDXGkQ-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=WINDOWS-1252 Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 207.211.31.81 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 20/11/19 19:45, Eduardo Habkost wrote: > On Wed, Nov 20, 2019 at 06:37:53PM +0100, Paolo Bonzini wrote: >> This allows using "-cpu Haswell,+vmx", which we did not really want to >> support in QEMU but was produced by Libvirt when using the "host-model" >> CPU model. >=20 > I understand guest ABI compatibility is not a concern, but I > don't remember how we guarantee it won't break by accident if > somebody tries to live migrate a VM. I'm not sure I understand the question, but I can answer the second part: > What is supposed to happen today if trying to live migrate a VM > using "-cpu Haswell,+vmx"? Before 4.2: same guest ABI compatibility as "-cpu host". 4.2+: ABI compatibility is preserved, because each named CPU model can be given a precise set of features that are matched against the host (and are subject to check/enforce). 4.1->4.2: the ABI *should* be preserved if you're running "-cpu SandyBridge,+vmx" on an actual Sandy Bridge, but some VMX features will disappear after live migration if e.g. you're running "-cpu SandyBridge,+vmx" on a Haswell. Host-model should be fine though. Paolo