From mboxrd@z Thu Jan 1 00:00:00 1970 From: Julien Grall Subject: Re: Criteria for dom0_gnttab_start Date: Tue, 21 Oct 2014 13:12:38 +0100 Message-ID: <54464DB6.7080509@linaro.org> References: <1413893074.23337.31.camel@citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1413893074.23337.31.camel@citrix.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Ian Campbell , Vijay Kilari Cc: Prasun Kapoor , "xen-devel@lists.xen.org" , manishjaggi.oss@gmail.com, Stefano Stabellini List-Id: xen-devel@lists.xenproject.org On 10/21/2014 01:04 PM, Ian Campbell wrote: > On Tue, 2014-10-21 at 17:24 +0530, Vijay Kilari wrote: >> What is the criteria for setting dom0_gnttab_start and size for a >> platform. > > It simply needs to be an area of the IPA address space which is not > populated by anything else. Since dom0's MMIO space is mapped 1:1 with > the host PA address space it seems easiest/safest to find a hole in the > real physical space and use that. > > If there is no such hole available then using the space occupied by some > device which is not passed to dom0 (e.g. is blacklisted, or used by Xen) > will suffice. > > For an arm32 platform it should be below 4G. Even on aarch64 platform, it will be better to have this range below 4G. I'm thinking about having a 32 bit DOM0 on top on a 64 bit Xen. Though, this may not happen often but we are currently supported this possibility for DOM0. Regards, -- Julien Grall