From mboxrd@z Thu Jan 1 00:00:00 1970 From: Julien Grall Subject: Re: [PATCH v2 01/20] xen: Add Xen specific page definition Date: Fri, 24 Jul 2015 14:03:14 +0100 Message-ID: <55B23792.5090802__33954.7770949595$1437743215$gmane$org@citrix.com> References: <1436474552-31789-1-git-send-email-julien.grall@citrix.com> <1436474552-31789-2-git-send-email-julien.grall@citrix.com> <55B20540.3020000@citrix.com> <55B207C6.4020300@citrix.com> <55B209D9.1080602@citrix.com> <55B20ABE.7000609@citrix.com> <55B214C5.3020501@citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mail6.bemta3.messagelabs.com ([195.245.230.39]) by lists.xen.org with esmtp (Exim 4.72) (envelope-from ) id 1ZIcem-0003mz-V0 for xen-devel@lists.xenproject.org; Fri, 24 Jul 2015 13:04:57 +0000 In-Reply-To: <55B214C5.3020501@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: David Vrabel , xen-devel@lists.xenproject.org Cc: ian.campbell@citrix.com, Boris Ostrovsky , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, stefano.stabellini@eu.citrix.com List-Id: xen-devel@lists.xenproject.org On 24/07/15 11:34, David Vrabel wrote: > On 24/07/15 10:51, Julien Grall wrote: >> On 24/07/15 10:48, David Vrabel wrote: >>> On 24/07/15 10:39, Julien Grall wrote: >>>> Hi David, >>>> >>>> On 24/07/15 10:28, David Vrabel wrote: >>>>> On 09/07/15 21:42, Julien Grall wrote: >>>>>> The Xen hypercall interface is always using 4K page granularity on ARM >>>>>> and x86 architecture. >>>>>> >>>>>> With the incoming support of 64K page granularity for ARM64 guest, it >>>>>> won't be possible to re-use the Linux page definition in Xen drivers. >>>>>> >>>>>> Introduce Xen page definition helpers based on the Linux page >>>>>> definition. They have exactly the same name but prefixed with >>>>>> XEN_/xen_ prefix. >>>>>> >>>>>> Also modify page_to_pfn to use new Xen page definition. >>>>>> >>>>>> Signed-off-by: Julien Grall >>>>>> Cc: Konrad Rzeszutek Wilk >>>>>> Cc: Boris Ostrovsky >>>>>> Cc: David Vrabel >>>>>> --- >>>>>> I'm wondering if we should drop page_to_pfn has the macro will likely >>>>>> misuse when Linux is using 64KB page granularity. >>>>> >>>>> I think we want xen_gfn_to_page() and xen_page_to_gfn() and Xen >>>>> front/back drivers never deal with PFNs only GFNs. >>>> >>>> What is xen_gfn_to_page and xen_page_to_gfn? Neither Linux, nor my >>>> series have them. >>> >>> I suggesting that you introduce these. >> >> It's still not clear to me what you are suggesting here... Do you >> suggest to rename xen_pfn_to_page and xen_page_to_pfn by xen_gfn_to_page >> and xen_page_to_gfn? > > Effectively, yes but it would be better to think that: > > PFNs index guest-sized pages (which may be 64 KiB). > > GFNs index Xen-sized pages (which is always 4 KiB). If I'm understanding correctly you mean: #define xen_page_to_gfn(page) \ ((page_to_pfn(page) << PAGE_SHIFT) >> XEN_PAGE_SHIFT)) static page_to_mfn(struct page *page) { return pfn_to_mfn(xen_page_to_gfn(page)); } Although in some place you are suggesting to use: xen_page_to_gfn(virt_to_page(info->intf)) (see patch #11) where it suggests to rename page_to_mfn in xen_page_to_gfn. I think it would make more sense to use the latter one. We would also need to name to describe a PFN (pseudo-physical frame number based on xen/include/xen/mm.h) but with 4K granularity and not the Linux granularity. It's useful to have it in some place in order to iter on the 4K pfn (see gnttab_foreach_grant and xen_apply_to_page). Maybe xpfn for Xen pseudo-physical frame number? I will preprend some patches into this serie to rename the function with their correct naming. I have in mind pfn_to_mfn which should be name into pfn_to_gfn given the usage. Similarly, this function is mis-used on ARM because the function may return an MFN where we expect a GFN. Regards, -- Julien Grall