Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1034058AbcJRQIo (ORCPT ); Tue, 18 Oct 2016 12:08:44 -0400 Received: from mx2.suse.de ([195.135.220.15]:32925 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1031000AbcJRQIe (ORCPT ); Tue, 18 Oct 2016 12:08:34 -0400 Subject: Re: [Xen-devel] [PATCH 6/8] xen/pvh: Initialize grant table for PVH guests To: Boris Ostrovsky , 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: Juergen Gross Message-ID: Date: Tue, 18 Oct 2016 18:08:31 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.4.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1204 Lines: 34 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(). So for PV(H) we don't need to balloon this memory back in as it was never shadowed by a grant. Juergen