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bh=H1+mhsgheS86cvlVGs4Uzh3qfyVBuk3U376R2uePSGY=; b=JTOFuWSWxuxh1YxuM1KuznvrvlI/ibKe1qF11ZNkHPUVtCzu5V9HC6cdoP3aX7nflJCrfF pGGTHNZTf8tCLuvsc6e+4lYYUTYC4AaBV1q2Owvu7tTYIlcX0qq2EupK6E1u9gvvrsd6tA 08QZB04xHWiVp+lXQP0n8C3LF/2+e6g= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-377-PUy5c4_KNRe6jC3NsiDuDQ-1; Mon, 04 Jan 2021 13:29:08 -0500 X-MC-Unique: PUy5c4_KNRe6jC3NsiDuDQ-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 3D99A107ACE3 for ; Mon, 4 Jan 2021 18:29:07 +0000 (UTC) Received: from localhost (ovpn-116-153.rdu2.redhat.com [10.10.116.153]) by smtp.corp.redhat.com (Postfix) with ESMTP id 0518B74AA0; Mon, 4 Jan 2021 18:29:06 +0000 (UTC) Date: Mon, 4 Jan 2021 13:29:06 -0500 From: Eduardo Habkost To: Vitaly Kuznetsov Subject: Re: [PATCH 5/5] i386: provide simple 'hyperv=on' option to x86 machine types Message-ID: <20210104182906.GD18467@habkost.net> References: <20201119103221.1665171-1-vkuznets@redhat.com> <20201119103221.1665171-6-vkuznets@redhat.com> <20201216205202.GJ3140057@habkost.net> <20201218181340.5e398280@redhat.com> <87r1n0j20n.fsf@vitty.brq.redhat.com> MIME-Version: 1.0 In-Reply-To: <87r1n0j20n.fsf@vitty.brq.redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=ehabkost@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Received-SPF: pass client-ip=216.205.24.124; envelope-from=ehabkost@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -29 X-Spam_score: -3.0 X-Spam_bar: --- X-Spam_report: (-3.0 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.243, 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: Igor Mammedov , Marcelo Tosatti , qemu-devel@nongnu.org, Paolo Bonzini Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Mon, Jan 04, 2021 at 01:54:32PM +0100, Vitaly Kuznetsov wrote: > Igor Mammedov writes: > > >> > > >> > + /* Hyper-V features enabled with 'hyperv=on' */ > >> > + x86mc->default_hyperv_features = BIT(HYPERV_FEAT_RELAXED) | > >> > + BIT(HYPERV_FEAT_VAPIC) | BIT(HYPERV_FEAT_TIME) | > >> > + BIT(HYPERV_FEAT_CRASH) | BIT(HYPERV_FEAT_RESET) | > >> > + BIT(HYPERV_FEAT_VPINDEX) | BIT(HYPERV_FEAT_RUNTIME) | > >> > + BIT(HYPERV_FEAT_SYNIC) | BIT(HYPERV_FEAT_STIMER) | > >> > + BIT(HYPERV_FEAT_FREQUENCIES) | BIT(HYPERV_FEAT_REENLIGHTENMENT) | > >> > + BIT(HYPERV_FEAT_TLBFLUSH) | BIT(HYPERV_FEAT_EVMCS) | > >> > + BIT(HYPERV_FEAT_IPI) | BIT(HYPERV_FEAT_STIMER_DIRECT); > > I'd argue that feature bits do not belong to machine code at all. > > If we have to involve machine at all then it should be a set property/value pairs > > that machine will set on CPU object (I'm not convinced that doing it > > from machine code is good idea though). > > > > These are 'features' and not feature bits. 'Bits' here are just our > internal (to QEMU) representation of which features are enable and which > are not, we could've just used booleans instead. These feature, when > enabled, will result in some CPUID changes (not 1:1) but I don't see how > it's different from > > " -machine q35,accel=kvm " > > which also results in CPUID changes. This is a good point, although having accel affect CPUID bits was also a source of complexity for query-cpu-model-expansion and other QMP queries. > > The main reason for putting this to x86 machine type is versioning, as > we go along we will (hopefully) be implementing more and more Hyper-V > features but we want to provide 'one knob to rule them all' but do it in > a way that will allow migration. We already have 'hv_passthrough' for > CPU. I agree completely that the set of bits needs to be on MachineClass. We just need to agree on the external interface. > > >> > > >> > + if (x86ms->hyperv_enabled) { > >> > + feat = x86mc->default_hyperv_features; > >> > + /* Enlightened VMCS is only available on Intel/VMX */ > >> > + if (!cpu_has_vmx(&cpu->env)) { > >> > + feat &= ~BIT(HYPERV_FEAT_EVMCS); > >> > + } > >> > + > >> > + cpu->hyperv_features |= feat; > > that will ignore features user explicitly doesn't want, > > ex: > > -machine hyperv=on -cpu foo,hv-foo=off > > > > Existing 'hv_passthrough' mode can also affect the result. Personally, I > don't see where 'hv-foo=off' is needed outside of debugging and these > use-cases can probably be covered by explicitly listing required > features but I'm not against making this work, shouldn't be hard. I'm all for not wasting time supporting use cases that are not necessary in practice. We just need to document the expected behavior clearly, whatever we decide to do. > > > not sure we would like to introduce such invariant, > > in normal qom property handling the latest set property should have effect > > (all other invariants we have in x86 cpu property semantics are comming from legacy handling > > and I plan to deprecate them (it will affect x86 and sparc cpus) so CPUs will behave like > > any other QOM object when it come to property handling) > > > > anyways it's confusing a bit to have cpu flags to come from 2 different places > > > > -cpu hyperv-use-preset=on,hv-foo=off > > > > looks less confusing and will heave expected effect > > > > Honestly, 'hyperv-use-preset' is confusing even to me :-) > > What if we for a second stop thinking about Hyper-V features being CPU > features only, e.g. if we want to create Dynamic Memory or PTP or any > other Hyper-V specific device in a simple way? We'll have to put these > under machine type. I agree. Hyper-V is not just a set of CPU features. Also, those two approaches are not mutually exclusive. "-machine hyperv=on" can be implemented internally using "hyperv-use-preset=on" if necessary. I don't think it has to, however. -- Eduardo