From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.5 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E80EEC433DB for ; Fri, 12 Feb 2021 14:14:41 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 91A1F64E3D for ; Fri, 12 Feb 2021 14:14:41 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 91A1F64E3D Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:34770 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lAZDU-0005Yy-Lz for qemu-devel@archiver.kernel.org; Fri, 12 Feb 2021 09:14:40 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:56064) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lAZC5-0004WX-Dg for qemu-devel@nongnu.org; Fri, 12 Feb 2021 09:13:13 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:46356) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1lAZC3-0006lZ-Kw for qemu-devel@nongnu.org; Fri, 12 Feb 2021 09:13:13 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1613139189; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=QOkaciXChLyUtxoj8LAxNUifh+cOdeyr2yzZQNdPl2E=; b=ZGyBtJX5RYDAU5Pi1bI5jzWDjshZSgXNdf/R0pZOghTEgdH2f3C7Bbc6SOt4qbADomPZos NnPBB09g/0V6eOV9Q3t4rfVJxLNweav3lylS4sIac8FP4UviPL0BTwxqWfMpAtMEgQ74Xl Q0hNRPB/ItL+6Y2R1oCAKEA/baTNXC0= 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-592-R_zCc5pZNWqjadGtzzIzWw-1; Fri, 12 Feb 2021 09:13:08 -0500 X-MC-Unique: R_zCc5pZNWqjadGtzzIzWw-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 6B201CE647 for ; Fri, 12 Feb 2021 14:13:07 +0000 (UTC) Received: from localhost (unknown [10.40.208.60]) by smtp.corp.redhat.com (Postfix) with ESMTP id 085B51B5AB; Fri, 12 Feb 2021 14:13:01 +0000 (UTC) Date: Fri, 12 Feb 2021 15:12:59 +0100 From: Igor Mammedov To: Vitaly Kuznetsov Subject: Re: [PATCH v4 16/21] i386: track explicit 'hv-*' features enablement/disablement Message-ID: <20210212151259.3db7406f@redhat.com> In-Reply-To: <87tuqhllmn.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> 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=63.128.21.124; envelope-from=imammedo@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" On Fri, 12 Feb 2021 09:45:52 +0100 Vitaly Kuznetsov wrote: > 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. When minimum supported by QEMU kernel version gets there, you can remove scratch CPU in QEMU (if hyperv will remain its sole user). writing your own property parser like in this series, is possible too but it adds extra fields to track state and hard to follow logic. On top it adds a lot of churn by switching hv_ features to dynamic properties, which is not necessary if scratch CPU approach is used. Please try reusing scratch CPU approach, see kvm_arm_get_host_cpu_features() for an example. You will very likely end up with simpler series, compared to reinventing wheel. in proto would look like: * kvm_init: hv_passthrough_cached = scratch_cpu->hyperv_features * property parsing time: x86_hv_passthrough_set() cpu->hyperv_features = hv_passthrough_cached all other features handled by generic property parsing, you don't have to do any special handling for them. * cpu_relalize() hv_expand() to check for dependencies, conflicts availability of features.