Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S938782AbcJRQjZ (ORCPT ); Tue, 18 Oct 2016 12:39:25 -0400 Received: from userp1040.oracle.com ([156.151.31.81]:23479 "EHLO userp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S938478AbcJRQjS (ORCPT ); Tue, 18 Oct 2016 12:39:18 -0400 Subject: Re: [Xen-devel] [PATCH 6/8] xen/pvh: Initialize grant table for PVH guests To: Juergen Gross , Konrad Rzeszutek Wilk References: <1476468318-24422-1-git-send-email-boris.ostrovsky@oracle.com> <1476468318-24422-7-git-send-email-boris.ostrovsky@oracle.com> <20161014191923.GD16777@localhost.localdomain> <20161014195134.GA22782@char.us.oracle.com> Cc: david.vrabel@citrix.com, xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org, roger.pau@citrix.com From: Boris Ostrovsky Message-ID: <467c1dd5-80a7-4079-ad49-69883fb9f076@oracle.com> Date: Tue, 18 Oct 2016 12:40:45 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.3.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit X-Source-IP: aserv0022.oracle.com [141.146.126.234] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1422 Lines: 41 On 10/18/2016 12:08 PM, Juergen Gross wrote: > On 14/10/16 22:02, Boris Ostrovsky wrote: >> On 10/14/2016 03:51 PM, Konrad Rzeszutek Wilk wrote: >>> On Fri, Oct 14, 2016 at 03:43:19PM -0400, Boris Ostrovsky wrote: >>>> On 10/14/2016 03:19 PM, Konrad Rzeszutek Wilk wrote: >>>>> On Fri, Oct 14, 2016 at 02:05:16PM -0400, Boris Ostrovsky wrote: >>>>> >>>>> Perhaps add in here: >>>>> >>>>> PVH is like PV in that there are no PCI devices - which HVM >>>>> code would piggyback on to find the Xen PCI platform device and >>>>> use its MMIO space to stash the grants in. >>>>> >>>>> For PVH we balloon out memory and stash the grants in there. >>>>> >>>>> (Which begs the next question - where and when do we balloon out the >>>>> normal memory back in?) >>>> Are you saying that we should get back memory that we gave to grant tables? >>> Yes. >>> >>> In pure HVM that area is MMIO - which hvmloader has balloonned out. >>> >>> The hvmloader then balloons that number of pages back at the end of >>> guest memory (after 4GB). >> We don't do this for PV though, do we? > Uuh, kind of. We try to allocate granted pages from the ballooned area. > See gnttab_alloc_pages(). I meant that we don't give memory back for PV. > > So for PV(H) we don't need to balloon this memory back in as it was > never shadowed by a grant. Is it *never* or *may or may not be* shadowed? (I assume "shadowed" means "used for" here.) -boris