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[91.219.240.2]) by smtp.gmail.com with ESMTPSA id t11sm3189112edd.1.2021.02.11.00.30.54 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 11 Feb 2021 00:30:54 -0800 (PST) From: Vitaly Kuznetsov To: Eduardo Habkost , =?utf-8?Q?Daniel_P=2E_Berrang?= =?utf-8?Q?=C3=A9?= Subject: Re: [PATCH v4 00/19] i386: KVM: expand Hyper-V features early and provide simple 'hv-default=on' option In-Reply-To: <20210210174652.GE1420762@habkost.net> References: <20210210164033.607612-1-vkuznets@redhat.com> <20210210165606.GM1240644@redhat.com> <20210210174652.GE1420762@habkost.net> Date: Thu, 11 Feb 2021 09:30:53 +0100 Message-ID: <87ft23m2f6.fsf@vitty.brq.redhat.com> MIME-Version: 1.0 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=vkuznets@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Received-SPF: pass client-ip=216.205.24.124; envelope-from=vkuznets@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -33 X-Spam_score: -3.4 X-Spam_bar: --- X-Spam_report: (-3.4 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.568, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=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: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Paolo Bonzini , Marcelo Tosatti , qemu-devel@nongnu.org, Igor Mammedov Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Eduardo Habkost writes: > On Wed, Feb 10, 2021 at 04:56:06PM +0000, Daniel P. Berrang=C3=A9 wrote: >> On Wed, Feb 10, 2021 at 05:40:12PM +0100, Vitaly Kuznetsov wrote: >> > Changes since v3: >> > - Make 'hv-default' override 'hv-*' options which were already set=20 >> > (e.g. 'hv-feature=3Don,hv-default' case) [Igor]. Make 'hv-passthroug= h' >> > behave the same way. >> > - Add "i386: be more picky about implicit 'hv-evmcs' enablement" patch= to avoid >> > enabling 'hv-evmcs' with hv-default/hv-passthrough when guest CPU la= cks VMX. >> > - Add "i386: support 'hv-passthrough,hv-feature=3Doff' on the command = line" patch >> > to make 'hv-passthrough' semantics match the newly introduced 'hv-de= fault'. >> > - Add "i386: track explicit 'hv-*' features enablement/disablement" pa= tch to >> > support the above mentioned changes. >> > - Expand qtest to check the above mentioned improvements. >> >=20 >> > Original description: >> >=20 >> > Upper layer tools like libvirt want to figure out which Hyper-V featur= es are >> > supported by the underlying stack (QEMU/KVM) but currently they are un= able to >> > do so. We have a nice 'hv_passthrough' CPU flag supported by QEMU but = it has >> > no effect on e.g. QMP's=20 >> >=20 >> > query-cpu-model-expansion type=3Dfull model=3D{"name":"host","props":{= "hv-passthrough":true}} >> >=20 >> > command as we parse Hyper-V features after creating KVM vCPUs and not = at >> > feature expansion time. To support the use-case we first need to make= =20 >> > KVM_GET_SUPPORTED_HV_CPUID ioctl a system-wide ioctl as the existing >> > vCPU version can't be used that early. This is what KVM part does. Wit= h >> > that done, we can make early Hyper-V feature expansion (this series). >> >=20 >> > In addition, provide a simple 'hv-default' option which enables (and >> > requires from KVM) all currently supported Hyper-V enlightenments. >> > Unlike 'hv-passthrough' mode, this is going to be migratable. >>=20 >> How is it going to be migratable if the semantics vary depending on >> the host kernel KVM reporting features, because different kernels >> will expose different features ? > > "all currently supported" in this context means "all features > supported when the machine type was added", not "all features > supported by the host kernel". Yes, exactly. 'hv-passthrough' enables 'everything supported by the host' and this is not migratable. 'hv-default' requires a certain set of features (depending on the machine type) so the VM won't start if the host lacks something. --=20 Vitaly