From mboxrd@z Thu Jan 1 00:00:00 1970 From: Julien Grall Subject: Re: [PATCH] libxc: introduce a per architecture scratch pfn for temporary grant mapping Date: Thu, 15 Jan 2015 13:20:05 +0000 Message-ID: <54B7BE85.5080704@linaro.org> References: <1421179848-31833-1-git-send-email-julien.grall@linaro.org> <54B66805.4080902@citrix.com> <20150115104515.GA51181@deinos.phlegethon.org> <54B7BD3F.7090107@citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mail6.bemta4.messagelabs.com ([85.158.143.247]) by lists.xen.org with esmtp (Exim 4.72) (envelope-from ) id 1YBkLj-00024D-Jz for xen-devel@lists.xenproject.org; Thu, 15 Jan 2015 13:20:35 +0000 Received: by mail-we0-f174.google.com with SMTP id k48so14643620wev.5 for ; Thu, 15 Jan 2015 05:20:34 -0800 (PST) In-Reply-To: <54B7BD3F.7090107@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: Andrew Cooper , Tim Deegan Cc: Wei Liu , Ian Campbell , Stefano Stabellini , Ian Jackson , Jan Beulich , xen-devel@lists.xenproject.org, =?windows-1252?Q?Roger_Pau_Monn=E9?= List-Id: xen-devel@lists.xenproject.org On 15/01/15 13:14, Andrew Cooper wrote: > For things like grant tables, the toolstack is already capable of using > add_to_physmap to make the pages mappable, but this is inefficient and > possibly interferes with the guest physical layout. I propose a short > circuit of this which allows the toolstack to map any legitimate physmap > spaces directly, without having to shuffle them in and out of the > physmap. i.e. a map foreign hypercall which takes {domid, space, idx} as > parameters rather than {domid, gfn}. > > For the magic pages, this proposal creates a secondary address space, > which is intended never for the guest to be able to map. This can > remove all the current "magic pages" which live in the low MMIO hole > (ioreq, bufioreq, mem_event rings, etc), and prevents the need for > emulation pages ever to be accessible to the guest. If I'm not mistaken a such solution would require modification in the kernel. So we would have to keep compatibility with older kernel. Regards, -- Julien Grall