From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Vrabel Subject: Re: [PATCH 1/5] xen/netback: Use xenballooned pages for comms Date: Wed, 19 Oct 2011 17:32:50 +0100 Message-ID: <4E9EFBB2.6050206@citrix.com> References: <1318969583-23902-1-git-send-email-dgdegra@tycho.nsa.gov> <1318969583-23902-2-git-send-email-dgdegra@tycho.nsa.gov> <1319015064.3385.80.camel@zakaz.uk.xensource.com> <4E9EE659.8090600@tycho.nsa.gov> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <4E9EE659.8090600@tycho.nsa.gov> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Daniel De Graaf Cc: "xen-devel@lists.xensource.com" , Ian Campbell , Konrad Rzeszutek Wilk List-Id: xen-devel@lists.xenproject.org On 19/10/11 16:01, Daniel De Graaf wrote: > On 10/19/2011 05:04 AM, Ian Campbell wrote: >> On Tue, 2011-10-18 at 21:26 +0100, Daniel De Graaf wrote: >>> For proper grant mappings, HVM guests require pages allocated using >>> alloc_xenballooned_pages instead of alloc_vm_area. >>> >>> Signed-off-by: Daniel De Graaf >>> --- [...] >> Could you also explain where the requirement to use xenballooned pages >> and not alloc_vm_area comes from in your commit message. > > (Will move to commit message). In PV guests, it is sufficient to only > reserve kernel address space for grant mappings because Xen modifies the > mappings directly. HVM guests require that Xen modify the GFN-to-MFN > mapping, so the pages being remapped must already be allocated. Pages > obtained from alloc_xenballooned_pages have valid GFNs not currently > mapped to an MFN, so are available to be used in grant mappings. Why doesn't (or can't?) Xen add new entries to the GFN-to-MFN map? Or why hasn't it reserved a range of GFNs in the map for this? David