From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sheng Yang Subject: Re: [PATCH][v2] Hybrid extension support in Xen Date: Tue, 2 Feb 2010 21:52:27 +0800 Message-ID: <201002022152.27984.sheng@linux.intel.com> References: Mime-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Keir Fraser Cc: Ian Campbell , "xen-devel@lists.xensource.com" List-Id: xen-devel@lists.xenproject.org On Tuesday 02 February 2010 21:35:23 Keir Fraser wrote: > On 02/02/2010 11:22, "Ian Campbell" wrote: > > On Tue, 2010-02-02 at 08:16 +0000, Sheng Yang wrote: > >> +/* Reserve 128KB for grant table */ > >> +#define GNTTAB_MEMBASE 0xfbfe0000 > >> +#define GNTTAB_MEMSIZE 0x20000 > > > > Why is this necessary? Isn't the grant table contained within one of the > > BARS on the virtual PCI device? What needs grant tables for prior to the > > kernel finding the PCI device which necessitates hardcoding these > > addresses in both guest and hypervisor? > > I didn't even find where these get used, except to reserve an area in e820, > and it wasn't clear why that reservation is necessary. > It has been used in the last [6/6] patch of Linux kernel side, which would use the pages to map grant table. It works the same as the MMIO region in PVonHVM device. Reserve it in BIOS because we think it's more elegant than depends on QEmu to provide the reserved memory space. -- regards Yang, Sheng