From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932663AbbFWNij (ORCPT ); Tue, 23 Jun 2015 09:38:39 -0400 Received: from smtp02.citrix.com ([66.165.176.63]:49864 "EHLO SMTP02.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754806AbbFWNia (ORCPT ); Tue, 23 Jun 2015 09:38:30 -0400 X-IronPort-AV: E=Sophos;i="5.13,665,1427760000"; d="scan'208";a="277686031" Date: Tue, 23 Jun 2015 14:37:45 +0100 From: Stefano Stabellini X-X-Sender: sstabellini@kaball.uk.xensource.com To: Julien Grall CC: David Vrabel , , , , , , , , , Subject: Re: [Xen-devel] [RFC 00/23] arm64: Add support for 64KB page granularity in Xen guest In-Reply-To: <5559D9C6.5010807@citrix.com> Message-ID: References: <1431622863-28575-1-git-send-email-julien.grall@citrix.com> <555614AB.9000006@citrix.com> <5559D9C6.5010807@citrix.com> User-Agent: Alpine 2.02 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" X-DLP: MIA1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 18 May 2015, Julien Grall wrote: > 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. We could at least introduce a few asserts, so that an ARM64 kernel build, that any x86 maintainers can easily and quickly do on their x86 machines, would spot these errors. From mboxrd@z Thu Jan 1 00:00:00 1970 From: stefano.stabellini@eu.citrix.com (Stefano Stabellini) Date: Tue, 23 Jun 2015 14:37:45 +0100 Subject: [Xen-devel] [RFC 00/23] arm64: Add support for 64KB page granularity in Xen guest In-Reply-To: <5559D9C6.5010807@citrix.com> References: <1431622863-28575-1-git-send-email-julien.grall@citrix.com> <555614AB.9000006@citrix.com> <5559D9C6.5010807@citrix.com> Message-ID: To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Mon, 18 May 2015, Julien Grall wrote: > 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. We could at least introduce a few asserts, so that an ARM64 kernel build, that any x86 maintainers can easily and quickly do on their x86 machines, would spot these errors.