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 6ACD9C433DF for ; Thu, 6 Aug 2020 00:18:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3FE9422CAE for ; Thu, 6 Aug 2020 00:18:52 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="cBZYcA/7" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726571AbgHFASv (ORCPT ); Wed, 5 Aug 2020 20:18:51 -0400 Received: from us-smtp-1.mimecast.com ([205.139.110.61]:38402 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726401AbgHFASs (ORCPT ); Wed, 5 Aug 2020 20:18:48 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1596673127; 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=MJRT7zSpZFX2l/kmuMRr1EyvfjsdpbwTsB/NIpr52Vg=; b=cBZYcA/7GAHNRRzBsyALhyCDGRM+oTxLJqWppDijrE9N3KA/BOpyQxDYcKWo1TH8kD28vS ndT4KdpUtRXKrhle+m2LJTKtYbCf8QEtLqzofr5tI5UBLN5MnoCGp97kcjilqd+zeC7uJa WLB6FhyrpdMECXDPzU18TjSRiyGeSZE= Received: from mail-wm1-f70.google.com (mail-wm1-f70.google.com [209.85.128.70]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-206-MnlcE6_NMjimNC79pnar9w-1; Wed, 05 Aug 2020 20:18:43 -0400 X-MC-Unique: MnlcE6_NMjimNC79pnar9w-1 Received: by mail-wm1-f70.google.com with SMTP id u144so3388210wmu.3 for ; Wed, 05 Aug 2020 17:18:43 -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=MJRT7zSpZFX2l/kmuMRr1EyvfjsdpbwTsB/NIpr52Vg=; b=sp1QF1UpGw7uUOnVVKbMYqlfwVH43pymW2SFOdfz1k58QEspp7O23FJwsbud8TtCS7 q1hceZ7/Aj9koVepuD2UAyqKH36Pzxk+fkv2dznsvYglteJ+2TeWwePE8i9nob3LRr1E aisBuLHoMNAAUC8PwE0meFPy+7FG8e4fyMpSH7t4cb/1tVFkOsdetgUMN2c1ZsWuzhQE bNzKKWc9saWqDG3uy2G+z+DB0MOPjDZljpYZ+0mKJaVfApAwYGbCqKGu3MUJ8moNsllA dq/AwGc3GHTvwZbWUA35aZsAZHLhsVW+3NBHS0FT7zm9pMK0QF8kz7HbHr58BgQI0GJx gpgA== X-Gm-Message-State: AOAM531UDlNXYKitLE5lje9fZxj6bst39YKLh9bjS1ivdQxAbeaPl0di FeDjr7L+ecO2fAQ0AZK2vaES6aZINUtDxZO9bnHaSTdvdgw7mdemO7XvgmStalZjRcO3HCCDwDN j/FCPDPJkkZe4 X-Received: by 2002:a05:6000:120c:: with SMTP id e12mr4761716wrx.354.1596673122253; Wed, 05 Aug 2020 17:18:42 -0700 (PDT) X-Google-Smtp-Source: ABdhPJyIUgCo8JmpOWMKH0QebbmqgBGb/LD/AwNZ3OZiBAbeJF9gifgU0NvT9R6cIHZlnE7BhL8MxA== X-Received: by 2002:a05:6000:120c:: with SMTP id e12mr4761704wrx.354.1596673122078; Wed, 05 Aug 2020 17:18:42 -0700 (PDT) Received: from redhat.com (bzq-79-177-102-128.red.bezeqint.net. [79.177.102.128]) by smtp.gmail.com with ESMTPSA id g3sm5035425wrb.59.2020.08.05.17.18.39 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 05 Aug 2020 17:18:41 -0700 (PDT) Date: Wed, 5 Aug 2020 20:18:37 -0400 From: "Michael S. Tsirkin" To: Jim Mattson Cc: Vitaly Kuznetsov , kvm list , Paolo Bonzini , Sean Christopherson , Wanpeng Li , Peter Xu , Julia Suvorova , Andy Lutomirski , LKML Subject: Re: [PATCH 2/3] KVM: x86: introduce KVM_MEM_PCI_HOLE memory Message-ID: <20200805201702-mutt-send-email-mst@kernel.org> References: <20200728143741.2718593-1-vkuznets@redhat.com> <20200728143741.2718593-3-vkuznets@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Wed, Aug 05, 2020 at 10:05:40AM -0700, Jim Mattson wrote: > On Tue, Jul 28, 2020 at 7:38 AM Vitaly Kuznetsov wrote: > > > > PCIe config space can (depending on the configuration) be quite big but > > usually is sparsely populated. Guest may scan it by accessing individual > > device's page which, when device is missing, is supposed to have 'pci > > hole' semantics: reads return '0xff' and writes get discarded. Compared > > to the already existing KVM_MEM_READONLY, VMM doesn't need to allocate > > real memory and stuff it with '0xff'. > > Note that the bus error semantics described should apply to *any* > unbacked guest physical addresses, not just addresses in the PCI hole. > (Typically, this also applies to the standard local APIC page > (0xfee00xxx) when the local APIC is either disabled or in x2APIC mode, > which is an area that kvm has had trouble with in the past.) Well ATM from KVM's POV unbacked -> exit to userspace, right? Not sure what you are suggesting here ... -- MST