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bh=3U+sTbDC/v+4z8/JRegb4z0gj7sqGf7Swk4F8YnsIGk=; b=DpBu/tszLSlryzvfqy4B7680JG2aPJCtqqrTU2GfUw9C7fCgEUimQ9UFIEz7SPG+BWIzQu 1E92GRCvyCvFW+OoI6NQeQrGnq/n2qh15aMh5wu/+sPa8+qvltlMRAaAXSkecAJQqbulhx Y4y6hZTmHC3BbnWU8uGncOjjHRm1gFo= 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-265-hVYKi9ziPiO9xFbVtb9Dfw-1; Wed, 26 May 2021 12:35:16 -0400 X-MC-Unique: hVYKi9ziPiO9xFbVtb9Dfw-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 489B9800D62 for ; Wed, 26 May 2021 16:35:15 +0000 (UTC) Received: from localhost (ovpn-114-21.rdu2.redhat.com [10.10.114.21]) by smtp.corp.redhat.com (Postfix) with ESMTP id 1198918966; Wed, 26 May 2021 16:35:14 +0000 (UTC) Date: Wed, 26 May 2021 12:35:14 -0400 From: Eduardo Habkost To: Vitaly Kuznetsov Subject: Re: [PATCH v6 10/19] i386: move eVMCS enablement to hyperv_init_vcpu() Message-ID: <20210526163514.izh52clpynbte747@habkost.net> References: <20210422161130.652779-1-vkuznets@redhat.com> <20210422161130.652779-11-vkuznets@redhat.com> <20210521212021.lsf2pzfu647ocqj3@habkost.net> <87mtsk734q.fsf@vitty.brq.redhat.com> MIME-Version: 1.0 In-Reply-To: <87mtsk734q.fsf@vitty.brq.redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 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: -31 X-Spam_score: -3.2 X-Spam_bar: --- X-Spam_report: (-3.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.371, 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_H4=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" On Mon, May 24, 2021 at 02:00:37PM +0200, Vitaly Kuznetsov wrote: [...] > >> @@ -1455,6 +1454,21 @@ static int hyperv_init_vcpu(X86CPU *cpu) > >> } > >> } > >> > >> + if (hyperv_feat_enabled(cpu, HYPERV_FEAT_EVMCS)) { > >> + uint16_t evmcs_version; > >> + > >> + ret = kvm_vcpu_enable_cap(cs, KVM_CAP_HYPERV_ENLIGHTENED_VMCS, 0, > >> + (uintptr_t)&evmcs_version); > >> + > >> + if (ret < 0) { > >> + fprintf(stderr, "Hyper-V %s is not supported by kernel\n", > >> + kvm_hyperv_properties[HYPERV_FEAT_EVMCS].desc); > >> + return ret; > >> + } > >> + > >> + cpu->hyperv_nested[0] = evmcs_version; > > > > Wait, won't this break guest ABI? Do we want to make > > HYPERV_FEAT_EVMCS a migration blocker until this is fixed? > > > > Could you please elaborate on the issue? I read the above is: when > evmcs' feature was requested, make an attempt to enable > KVM_CAP_HYPERV_ENLIGHTENED_VMCS, and bail out if this fails. Propagate > the the acquired evmcs version to 'cpu->hyperv_nested[]' otherwise. This will be visible to the guest at CPUID[0x4000000A].EAX, correct? You are initializing CPUID data with a value that change depending on the host. What is supposed to happen if live migrating to to a host with a different evmcs_version? -- Eduardo