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[91.219.240.2]) by smtp.gmail.com with ESMTPSA id o23sm553782ejx.69.2021.02.12.00.45.52 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 12 Feb 2021 00:45:53 -0800 (PST) From: Vitaly Kuznetsov To: Igor Mammedov Subject: Re: [PATCH v4 16/21] i386: track explicit 'hv-*' features enablement/disablement In-Reply-To: <20210211183555.2136b5c8@redhat.com> References: <20210210164033.607612-1-vkuznets@redhat.com> <20210210164033.607612-17-vkuznets@redhat.com> <20210211183555.2136b5c8@redhat.com> Date: Fri, 12 Feb 2021 09:45:52 +0100 Message-ID: <87tuqhllmn.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 Received-SPF: pass client-ip=170.10.133.124; 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=-0.569, 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 , drjones@redhat.com, Marcelo Tosatti , qemu-devel@nongnu.org, Eduardo Habkost Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Igor Mammedov writes: > On Wed, 10 Feb 2021 17:40:28 +0100 > Vitaly Kuznetsov wrote: > >> Sometimes we'd like to know which features were explicitly enabled and which >> were explicitly disabled on the command line. E.g. it seems logical to handle >> 'hv_passthrough,hv_feature=off' as "enable everything supported by the host >> except for hv_feature" but this doesn't seem to be possible with the current >> 'hyperv_features' bit array. Introduce 'hv_features_on'/'hv_features_off' >> add-ons and track explicit enablement/disablement there. >> >> Note, it doesn't seem to be possible to fill 'hyperv_features' array during >> CPU creation time when 'hv-passthrough' is specified and we're running on >> an older kernel without KVM_CAP_SYS_HYPERV_CPUID support. To get the list >> of the supported Hyper-V features we need to actually create KVM VCPU and >> this happens much later. > > seems to me that we are returning back to +-feat parsing, this time only for > hyperv. > I'm not sure I like it back, especially considering we are going to > drop "-feat" priority for x86. > > now about impossible, see arm/kvm/virt, they create a 'sample' VCPU at KVM > init time to probe for some CPU features in advance. You can use similar > approach to prepare value for hyperv_features. > KVM_CAP_SYS_HYPERV_CPUID is supported since 5.11 and eventually it'll make it to all kernels we care about so I'd really like to avoid any 'sample' CPUs for the time being. On/off parsing looks like a much lesser evil. -- Vitaly