Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755584AbaBTSR3 (ORCPT ); Thu, 20 Feb 2014 13:17:29 -0500 Received: from smtp.citrix.com ([66.165.176.89]:12486 "EHLO SMTP.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755240AbaBTSR1 (ORCPT ); Thu, 20 Feb 2014 13:17:27 -0500 X-IronPort-AV: E=Sophos;i="4.97,513,1389744000"; d="scan'208";a="104423979" Date: Thu, 20 Feb 2014 18:17:19 +0000 From: Stefano Stabellini X-X-Sender: sstabellini@kaball.uk.xensource.com To: Zoltan Kiss CC: Stefano Stabellini , Konrad Rzeszutek Wilk , Boris Ostrovsky , David Vrabel , 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: <53063D2B.1040502@citrix.com> Message-ID: References: <1392238453-26147-1-git-send-email-zoltan.kiss@citrix.com> <5301F74E.3070107@citrix.com> <53063D2B.1040502@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, 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 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? -- 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/