Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755522AbaBTS1C (ORCPT ); Thu, 20 Feb 2014 13:27:02 -0500 Received: from smtp02.citrix.com ([66.165.176.63]:26860 "EHLO SMTP02.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753552AbaBTS1A (ORCPT ); Thu, 20 Feb 2014 13:27:00 -0500 X-IronPort-AV: E=Sophos;i="4.97,513,1389744000"; d="scan'208";a="102733324" Date: Thu, 20 Feb 2014 18:26:53 +0000 From: Stefano Stabellini X-X-Sender: sstabellini@kaball.uk.xensource.com To: David Vrabel CC: Stefano Stabellini , Zoltan Kiss , Konrad Rzeszutek Wilk , Boris Ostrovsky , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , , , , =?UTF-8?Q?Roger_Pau_Monn=C3=A9?= , Jan Beulich , Ian Campbell Subject: Re: [PATCH v9] xen/grant-table: Avoid m2p_override during mapping In-Reply-To: <5306471D.1080809@citrix.com> Message-ID: References: <1392238453-26147-1-git-send-email-zoltan.kiss@citrix.com> <5301F74E.3070107@citrix.com> <53063D2B.1040502@citrix.com> <5306471D.1080809@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: MIA2 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 20 Feb 2014, David Vrabel wrote: > On 20/02/14 18:17, Stefano Stabellini wrote: > > On Thu, 20 Feb 2014, Zoltan Kiss wrote: > >> On 20/02/14 17:26, Stefano Stabellini wrote: > >>> On Mon, 17 Feb 2014, Zoltan Kiss wrote: > >>>> On 16/02/14 18:36, Stefano Stabellini wrote: > >>>>> On Wed, 12 Feb 2014, Zoltan Kiss wrote: > >>>>>> diff --git a/arch/arm/include/asm/xen/page.h > >>>>>> b/arch/arm/include/asm/xen/page.h > >>>>>> index e0965ab..4eaeb3f 100644 > >>>>>> --- a/arch/arm/include/asm/xen/page.h > >>>>>> +++ b/arch/arm/include/asm/xen/page.h > >>>>>> @@ -97,16 +97,15 @@ static inline pte_t *lookup_address(unsigned long > >>>>>> address, unsigned int *level) > >>>>>> return NULL; > >>>>>> } > >>>>>> > >>>>>> -static inline int m2p_add_override(unsigned long mfn, struct page > >>>>>> *page, > >>>>>> - struct gnttab_map_grant_ref *kmap_op) > >>>>>> -{ > >>>>>> - return 0; > >>>>>> -} > >>>>>> - > >>>>>> -static inline int m2p_remove_override(struct page *page, bool > >>>>>> clear_pte) > >>>>>> -{ > >>>>>> - return 0; > >>>>>> -} > >>>>>> +extern int set_foreign_p2m_mapping(struct gnttab_map_grant_ref > >>>>>> *map_ops, > >>>>>> + struct gnttab_map_grant_ref > >>>>>> *kmap_ops, > >>>>>> + struct page **pages, unsigned int > >>>>>> count, > >>>>>> + bool m2p_override); > >>>>>> + > >>>>>> +extern int clear_foreign_p2m_mapping(struct gnttab_unmap_grant_ref > >>>>>> *unmap_ops, > >>>>>> + struct gnttab_map_grant_ref > >>>>>> *kmap_ops, > >>>>>> + struct page **pages, unsigned int > >>>>>> count, > >>>>>> + bool m2p_override); > >>>>> > >>>>> Much much better. > >>>>> The only comment I have is about this m2p_override boolean parameter. > >>>>> m2p_override is now meaningless in this context, what we really want to > >>>>> let the arch specific implementation know is whether the mapping is a > >>>>> kernel only mapping or a userspace mapping. > >>>>> Testing for kmap_ops != NULL might even be enough, but it would not > >>>>> improve the interface. > >>>> gntdev is the only user of this, the kmap_ops parameter there is: > >>>> use_ptemod ? map->kmap_ops + offset : NULL > >>>> where: > >>>> use_ptemod = !xen_feature(XENFEAT_auto_translated_physmap); > >>>> So I think we can't rely on kmap_ops to decide whether we should > >>>> m2p_override > >>>> or not. > >>>> > >>>>> Is it possible to realize if the mapping is a userspace mapping by > >>>>> checking for GNTMAP_application_map in map_ops? > >>>>> Otherwise I would keep the boolean and rename it to user_mapping. > >>>> Sounds better, but as far as I see gntdev set that flag in > >>>> find_grant_ptes, > >>>> which is called only > >>>> > >>>> if (use_ptemod) { > >>>> err = apply_to_page_range(vma->vm_mm, vma->vm_start, > >>>> vma->vm_end - vma->vm_start, > >>>> find_grant_ptes, map); > >>>> > >>>> So if xen_feature(XENFEAT_auto_translated_physmap), we don't have > >>>> kmap_ops, > >>>> and GNTMAP_application_map is not set as well, but I guess we still need > >>>> m2p_override. Or not? I'm a bit confused, maybe because of Monday ... > >>> > >>> If xen_feature(XENFEAT_auto_translated_physmap) we shouldn't need the > >>> m2p_override. > >>> > >> > >> So it's safe to assume that we need m2p_override only if kmap_ops != NULL, and > >> we can avoid the extra bool parameter, is that correct? At least with the > >> current users of grant mapping it seems to be true. > >> In which case we don't need the wrappers for gnttab_[un]map_refs as well. > >> Actually the most of m2p_add/remove_override takes effect only if there is a > >> kmap_op parameter, but what about the rest of the code there? > > > > It is safe to assume that we only need the m2p_override if > > !xen_feature(XENFEAT_auto_translated_physmap). > > I wouldn't make any assumptions on kmap_ops != NULL. > > I think it is -- we only need the m2p override if we have userspace > mappings (where kmap_ops != 0). > > > I would remove the bool m2p_override parameter completely and determine > > whether we need to call the m2p_override functions from the x86 > > implementation of set/clear_foreign_p2m_mapping by checking > > xen_feature(XENFEAT_auto_translated_physmap). > > > > David, does it seem reasonable to you? > > That would miss the point of this patch which is to avoid adding to the > m2p_override for kernel only mappings. I meant checking !xen_feature(XENFEAT_auto_translated_physmap) && kmap_ops != 0 At least this way the "hack" would be entirely self contained in the arch specific code. -- 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/