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bh=D+vYrpgKqnhZbTBws518N40LyW3cDJLZheD49SCFb+4=; b=D1oASENO5J8nXmE3bze9yjbpgyeRVDgCI6MehEFlIcxmPL60vQdqkYuWa4QOD1HC9RM3bU 2N4x2InF2FFmFojdQ0tKY21XzGEH0jhEBrr2occui4uZucVj2p3UFREHpwXPtwKAkAPTBB XirIVa8chB8ji069RDsV3nyWBhI3c/k= 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-76-LHVeyTLbOFqYOy2Oi5Us-A-1; Tue, 23 Feb 2021 10:22:59 -0500 X-MC-Unique: LHVeyTLbOFqYOy2Oi5Us-A-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 8A2EA195D567 for ; Tue, 23 Feb 2021 15:19:52 +0000 (UTC) Received: from localhost (unknown [10.40.208.64]) by smtp.corp.redhat.com (Postfix) with ESMTP id AB1F95D9D0; Tue, 23 Feb 2021 15:19:50 +0000 (UTC) Date: Tue, 23 Feb 2021 16:19:48 +0100 From: Igor Mammedov To: Vitaly Kuznetsov Subject: Re: [PATCH v4 16/21] i386: track explicit 'hv-*' features enablement/disablement Message-ID: <20210223161948.56bf86c0@redhat.com> In-Reply-To: <87mtvw4d59.fsf@vitty.brq.redhat.com> References: <20210210164033.607612-1-vkuznets@redhat.com> <20210210164033.607612-17-vkuznets@redhat.com> <20210211183555.2136b5c8@redhat.com> <87tuqhllmn.fsf@vitty.brq.redhat.com> <20210212151259.3db7406f@redhat.com> <87k0rdl3er.fsf@vitty.brq.redhat.com> <20210212170113.30a902b2@redhat.com> <87eehhlnj5.fsf@vitty.brq.redhat.com> <20210215180106.7e573e6a@redhat.com> <87sg5xjj60.fsf@vitty.brq.redhat.com> <87mtvw4d59.fsf@vitty.brq.redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=imammedo@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=imammedo@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, 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" On Mon, 22 Feb 2021 11:20:34 +0100 Vitaly Kuznetsov wrote: > Vitaly Kuznetsov writes: > > > Igor Mammedov writes: > > > >>> > >>> We need to distinguish because that would be sane. > >>> > >>> Enlightened VMCS is an extension to VMX, it can't be used without > >>> it. Genuine Hyper-V doesn't have a knob for enabling and disabling it, > >> ... > >>> That bein said, if > >>> guest CPU lacks VMX it is counter-productive to expose EVMCS. However, > >>> there is a problem with explicit enablement: what should > >>> > >>> 'hv-passthrough,hv-evmcs' option do? Just silently drop EVMCS? Doesn't > >>> sound sane to me. > >> based on above I'd error out is user asks for unsupported option > >> i.e. no VMX -> no hv-evmcs - if explicitly asked -> error out > > > > That's what I keep telling you but you don't seem to listen. 'Scratch > > CPU' can't possibly help with this use-case because when you parse > > > > 'hv-passthrough,hv-evmcs,vmx=off' you > > > > 1) "hv-passthrough" -> set EVMCS bit to '1' as it is supported by the > > host. > > > > 2) 'hv-evmcs' -> keep EVMCS bit '1' > > > > 3) 'vmx=off' -> you have no idea where EVMCS bit came from. > > > > We have to remember which options were aquired from the host and which > > were set explicitly by the user. > > Igor, > > could you please comment on the above? In case my line of thought is > correct, and it is impossible to distinguish between e.g. > > 'hv-passthrough,hv-evmcs,-vmx' > and > 'hv-passthrough,-vmx' > > without a custom parser (written just exactly the way I did in this > version, for example) regardless of when 'hv-passthrough' is > expanded. E.g. we have the exact same problem with > 'hv-default,hv-evmcs,-vmx'. I that case I see no point in discussing right, if we need to distinguish between explicit and implicit hv-evmcs set by hv-passthrough custom parser probably the way to go. However do we need actually need to do it? I'd treat 'hv-passthrough,-vmx' the same way as 'hv-passthrough,hv-evmcs,-vmx' and it applies not only hv-evmcs but other features hv-passthrough might set (i.e. if whatever was [un]set by hv-passthrough in combination with other features results in invalid config, QEMU shall error out instead of magically altering host provided hv-passthrough value). something like: 'hv-passthrough,-vmx' when hv-passthrough makes hv-evmcs bit set should result in error_setg(errp,"'vmx' feature can't be disabled when hv-evmcs is enabled," " either enable 'vmx' or disable 'hv-evmcs' along with disabling 'vmx'" making host's features set, *magically* mutable, depending on other user provided features is a bit confusing. One would never know what hv-passthrough actually means, and if enabling/disabling 'random' feature changes it. It's cleaner to do just what user asked (whether implicitly or explicitly) and error out in case it ends up in nonsense configuration. > 'scratch CPUs' idea at this point because it is not going to change > anything at all ('hv_features_on' will stay, custom parsers will stay).g > > Am I missing something? >