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=-13.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_IN_DEF_DKIM_WL 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 5D1FDC43461 for ; Tue, 4 May 2021 16:53:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2EA19613C0 for ; Tue, 4 May 2021 16:53:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231739AbhEDQxy (ORCPT ); Tue, 4 May 2021 12:53:54 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33972 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230477AbhEDQxx (ORCPT ); Tue, 4 May 2021 12:53:53 -0400 Received: from mail-ot1-x335.google.com (mail-ot1-x335.google.com [IPv6:2607:f8b0:4864:20::335]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 18B28C061574 for ; Tue, 4 May 2021 09:52:58 -0700 (PDT) Received: by mail-ot1-x335.google.com with SMTP id g15-20020a9d128f0000b02902a7d7a7bb6eso2091371otg.9 for ; Tue, 04 May 2021 09:52:58 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=vdkFREewlZcIDmDynEQ1WiTK28L5oQeFHQvdWFt20H8=; b=sxCdv3gUS81WcMO5HZwVF/YY/aTx9nyBxnp72jMDhHxZyPo8dExNRLRe1h6NxXBlMF owEnVU/qRjK/grqsNFswIwo4RYalfY8Q9BT68HxVIq40oX3IyJTxisXf+RWQnlh6ksBl 8SdZm2T5mo3K/W5I/O0LXTqtqkeiiNn2CxxT9Vt+ceX3uOQxiO7wonFbVriU//TlbdQQ dMKjYUY4W6MxXbGp5N2i0WA0yxZSBT3oJGmalOomTLWDKimjaT0vvCzdn/5nhsegpqSO PptP4XzsvIuul9jIuRXwBty0YwD1ttzYoy2OOyJjqlFRletHTLL2OLQhqHzi4cLGdbo6 1cTQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=vdkFREewlZcIDmDynEQ1WiTK28L5oQeFHQvdWFt20H8=; b=QcT4hcl+nfwRrr6Cs0xIOs9cKNOwIyDx9AQ6aQDYQcjpf4BDfXl+3tFWrUKdAz8yib azStC8yD2/gF0flMz8ZSJxr0mkUXMuk9NnlpY9JmMqd9Wo2O6WFTZnwApn2weS2OFoSu sZHweoE7aL4l3bIJdUKIIhh/ljq9HfwbzTsqdpR7Z9CQ8opsRQhuVxgtHN4HueGZanEo EZv2YyIIE61ZGUHPLTAjJH/jfZ32ZIpFGY4qqQLZ93ZBlv+QPxpUti/ILFA+GS6Gcpo5 I031Llsf+gkq+/JigOBMtPBuA107xHlm7mPWgkJ1Y4E07zQZeXVdd+kbC0MYmxVumyQg JRCg== X-Gm-Message-State: AOAM532FKHFWZnbH3n9iXFhejkptj2vZJwurOgZlWHvdKvIhRd+F1X1b 7/uzmlPS8yYIZVPSPyXlTaMimehnml2mzkRcEtyhGg== X-Google-Smtp-Source: ABdhPJz4q/uVbItWDyl6QflQ4NHfG7as4jx8YVi70hHEkvZXmHwdIZxapwMixmihPdmvH/JJv8aCMvaA7Abj9xLlRHE= X-Received: by 2002:a05:6830:16c8:: with SMTP id l8mr20047502otr.56.1620147177249; Tue, 04 May 2021 09:52:57 -0700 (PDT) MIME-Version: 1.0 References: <20210428172729.3551-1-valeriy.vdovin@virtuozzo.com> <0d68dbc3-8462-7763-fbad-f3b895fcf6e6@redhat.com> <63e54361-0018-ad3b-fb2b-e5dba6a0f221@redhat.com> <048b3f3a-379d-cff3-20b6-fc74dd12a98f@openvz.org> <514b5373-c07b-ad34-5fba-f8850faf6d68@redhat.com> In-Reply-To: From: Jim Mattson Date: Tue, 4 May 2021 09:52:46 -0700 Message-ID: Subject: Re: [PATCH v4] KVM: x86: Fix KVM_GET_CPUID2 ioctl to return cpuid entries count To: Alexander Graf Cc: Paolo Bonzini , "Denis V. Lunev" , Sean Christopherson , Valeriy Vdovin , LKML , Jonathan Corbet , Vitaly Kuznetsov , Wanpeng Li , Joerg Roedel , Thomas Gleixner , Ingo Molnar , Borislav Petkov , x86@kernel.org, "H. Peter Anvin" , Shuah Khan , Aaron Lewis , Andrew Jones , Oliver Upton , Like Xu , kvm@vger.kernel.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Tue, May 4, 2021 at 2:26 AM Alexander Graf wrote: > > > > On 04.05.21 10:21, Paolo Bonzini wrote: > > > > On 04/05/21 10:15, Denis V. Lunev wrote: > >> As far as I understand only some testing within kernel now. > >> Though we have plans to expose it for QAPI as the series > >> in QEMU > >> [PATCH 1/2] qapi: fix error handling for x-vz-query-cpu-model-cpuid > >> [PATCH 2/2] qapi: blacklisted x-vz-query-cpu-model-cpuid in tests > >> is not coming in a good way. > >> The idea was to avoid manual code rework in QEMU and > >> expose collected model at least for debug. > > > > KVM_GET_CPUID2 as a VM ioctl cannot expose the whole truth about CPUID > > either, since it doesn't handle the TSX_CTRL_CPUID_CLEAR bit. Given > > that QEMU doesn't need KVM_GET_CPUID2; it only needs to save whatever it > > passed to KVM_SET_CPUID2. > > What if we instead deflect CPUID into user space so it can emulate it in > whatever way it likes? Is the performance difference going to be > relevant? Are people still using cpuid as barrier these days? What else would they use (in ring 3 code)? Sure, serialize is coming in Sapphire Rapids, but it will be 20+ years before kvm drops support for CPUs without serialize. > > Alex > > > > Amazon Development Center Germany GmbH > Krausenstr. 38 > 10117 Berlin > Geschaeftsfuehrung: Christian Schlaeger, Jonathan Weiss > Eingetragen am Amtsgericht Charlottenburg unter HRB 149173 B > Sitz: Berlin > Ust-ID: DE 289 237 879 > >