Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754021AbbERMYM (ORCPT ); Mon, 18 May 2015 08:24:12 -0400 Received: from smtp02.citrix.com ([66.165.176.63]:37947 "EHLO SMTP02.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752844AbbERMYI (ORCPT ); Mon, 18 May 2015 08:24:08 -0400 X-IronPort-AV: E=Sophos;i="5.13,453,1427760000"; d="scan'208";a="266060628" Message-ID: <5559D9C6.5010807@citrix.com> Date: Mon, 18 May 2015 13:23:34 +0100 From: Julien Grall User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Icedove/31.6.0 MIME-Version: 1.0 To: David Vrabel , Julien Grall , CC: , , , , , , , Subject: Re: [Xen-devel] [RFC 00/23] arm64: Add support for 64KB page granularity in Xen guest References: <1431622863-28575-1-git-send-email-julien.grall@citrix.com> <555614AB.9000006@citrix.com> In-Reply-To: <555614AB.9000006@citrix.com> Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: 7bit X-DLP: MIA1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1795 Lines: 46 Hi David, On 15/05/15 16:45, David Vrabel wrote: > On 14/05/15 18:00, Julien Grall wrote: >> Hi all, >> >> ARM64 Linux is supporting both 4KB and 64KB page granularity. Although, Xen >> hypercall interface and PV protocol are always based on 4KB page granularity. >> >> Any attempt to boot a Linux guest with 64KB pages enabled will result to a >> guest crash. >> >> This series is a first attempt to allow those Linux running with the current >> hypercall interface and PV protocol. >> >> This solution has been chosen because we want to run Linux 64KB in released >> Xen ARM version or/and platform using an old version of Linux DOM0. > > The key problem I see with this approach is the confusion between guest > page size and Xen page size. This is going to be particularly > problematic since the majority of development/usage will remain on x86 > where PAGE_SIZE == XEN_PAGE_SIZE. > > I think it would be nice to keep XEN_PAGE_SIZE etc out of front and > backend drivers. Perhaps with a suitable set of helper functions? Even with the helpers, we are not protected from any change in the frontend/backend that will impact 64K. It won't be possible to remove all the XEN_PAGE_* usage (there is a lots of places where adding helpers would not be possible) and we would still have to carefully review any changes. I think it may be possible to move the grant table splitting in helpers which would be helpful to support different grant size. Although, it would require a big amount of work at least in blkfront. Regards, -- Julien Grall -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/