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=-4.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,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 480E3C433E0 for ; Thu, 6 Aug 2020 16:58:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9ADCF2086A for ; Thu, 6 Aug 2020 16:58:21 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="ECmsgVcM" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729564AbgHFQ6U (ORCPT ); Thu, 6 Aug 2020 12:58:20 -0400 Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:32701 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1729795AbgHFQ5E (ORCPT ); Thu, 6 Aug 2020 12:57:04 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1596733022; 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: in-reply-to:in-reply-to:references:references; bh=JsQQ+Of14Jcox/vjqRSvLqdJ9OO0AZmQ6i3MKzbPweU=; b=ECmsgVcMzNpEWxJQ99HTAjC4QylaUFh2OgG6T21CvkiIg9O4Chec9vE5hL+436Bjhrjcao aFmRtf6itPkJKu6DKyIettse6Cl7U3R0g4ANecAXu385+UnOMUodg8rhVppxqAkY1NgNL7 2UNxBwXDMrTvNnQ8Z26CQTt8Wft0NYo= Received: from mail-wm1-f71.google.com (mail-wm1-f71.google.com [209.85.128.71]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-411-rrHo_498NTGxH0WE1SZq-A-1; Thu, 06 Aug 2020 08:19:35 -0400 X-MC-Unique: rrHo_498NTGxH0WE1SZq-A-1 Received: by mail-wm1-f71.google.com with SMTP id q15so4040151wmj.6 for ; Thu, 06 Aug 2020 05:19:35 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=JsQQ+Of14Jcox/vjqRSvLqdJ9OO0AZmQ6i3MKzbPweU=; b=mDoP3+93x3WKF6kpGW4UlV3yd0IWhq9NSDT0dc23oViI0al8W8IZOqFK2kCH8+OJs9 DZAed7wWri7oOm4bcmk6i7zZLDBp9t3Umrq2ILr3Z5bGYztyMt2270xEgJH2y5VYo9Ve T4q3mNlsHvnZeJDm3EWvZvwPdOWRbdOMzGbbj6opqP3VmtKTdAnbNstQnqCaTdNZOjnu aL6/g92TW5D7wx3zIjcFLWPm5vaZ6c06vbqV446vamjV4lhLClEc5E2LrnRPc4Q1K445 rDc8Vpybw95M/raiTsGjDE/jaGAMqSyRM4uRrX/Jli+sZ3OXff/l7SofmwQATecgcTiE sjjg== X-Gm-Message-State: AOAM533vfiNZ13XgEVpjmW7JfrTdVeovbJYklIaGPPiTezVtiY8/5Q0e UOmSLKto1RNDGbfDIbzhOG7RJA/q8v4lcWv4Ol/Da7QHLoJM4pF3jN2X+T/+RROk/+xmc+GEwZt Mp3xcbNW5k5zd X-Received: by 2002:a1c:5a41:: with SMTP id o62mr7903995wmb.16.1596716374338; Thu, 06 Aug 2020 05:19:34 -0700 (PDT) X-Google-Smtp-Source: ABdhPJzyIywm4grHWIEGGqRYHwakkz8CRdHAYx5VrR1wcD6mUEyChlrX/txPMAT79yt1vKaH9Ku0ng== X-Received: by 2002:a1c:5a41:: with SMTP id o62mr7903978wmb.16.1596716374170; Thu, 06 Aug 2020 05:19:34 -0700 (PDT) Received: from redhat.com (bzq-79-180-0-181.red.bezeqint.net. [79.180.0.181]) by smtp.gmail.com with ESMTPSA id n24sm6536082wmi.36.2020.08.06.05.19.32 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 06 Aug 2020 05:19:33 -0700 (PDT) Date: Thu, 6 Aug 2020 08:19:30 -0400 From: "Michael S. Tsirkin" To: Vitaly Kuznetsov Cc: kvm@vger.kernel.org, Paolo Bonzini , Sean Christopherson , Wanpeng Li , Jim Mattson , Peter Xu , Julia Suvorova , Andy Lutomirski , linux-kernel@vger.kernel.org Subject: Re: [PATCH 0/3] KVM: x86: KVM_MEM_PCI_HOLE memory Message-ID: <20200806081800-mutt-send-email-mst@kernel.org> References: <20200728143741.2718593-1-vkuznets@redhat.com> <20200805201851-mutt-send-email-mst@kernel.org> <873650p1vo.fsf@vitty.brq.redhat.com> <20200806055008-mutt-send-email-mst@kernel.org> <87wo2cngv6.fsf@vitty.brq.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87wo2cngv6.fsf@vitty.brq.redhat.com> Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Thu, Aug 06, 2020 at 01:39:09PM +0200, Vitaly Kuznetsov wrote: > "Michael S. Tsirkin" writes: > > > About the feature bit, I am not sure why it's really needed. A single > > mmio access is cheaper than two io accesses anyway, right? So it makes > > sense for a kvm guest whether host has this feature or not. > > We need to be careful and limit to a specific QEMU implementation > > to avoid tripping up bugs, but it seems more appropriate to > > check it using pci host IDs. > > Right, it's just that "running on KVM" is too coarse grained, we just > need a way to somehow distinguish between "known/good" and > "unknown/buggy" configurations. Basically it's not KVM, it's QEMU that is known good. QEMU vendor id in the pci host seems like a reasonable way to detect that. If someone reuses QEMU ID - I guess they better behave just like QEMU :) I also proposed only limiting this to register 0 (device id), will make it very unlikely this can break accidentally ... > -- > Vitaly