From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stefano Stabellini Subject: Re: [hybrid] : mmap pfn space... Date: Mon, 26 Mar 2012 11:37:46 +0100 Message-ID: References: <20120323110144.4b2f1d45@mantra.us.oracle.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20120323110144.4b2f1d45@mantra.us.oracle.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: Mukesh Rathor Cc: "Xen-devel@lists.xensource.com" , Ian Campbell , Stefano Stabellini List-Id: xen-devel@lists.xenproject.org On Fri, 23 Mar 2012, Mukesh Rathor wrote: > Hi Ian/Stefano, > > So, I'm back to using pfn space from maxphysaddr below. Stefano, you > suggested ballooning, but that would be just too slow. There are lot of > pages to be mapped, 4k at a time during guest creation, and I am afraid > ballooning and hypercalls to populate EPT will be pretty slow. > > OTOH, there is tons of address space available between max-physaddr and > max pfn in dom0. Stefano, your concern was stuff mapped there > causing problems in future. But we can always look at the e820 for > conflicts. Keeping things fast is important for us . > > Please let me know if you still have issues with my approach. I > believe this is what Ian is doing on ARM port. I think that we should explicitly allocate these pages/addresses and not rely on the fact that they are at a specific location that we deem safe for now. So if we explicitly introduce a new region at the end of the e820 that we mark as reserved and we use it for this, I would be OK with that. However we need to be careful because editing the e820 has proved to be challenging in the past. Also we would need to figure out a way to tell Linux that these reserved addresses are actually OK to be used. Maybe we need a new command line or hypercall for that.