Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755857AbaBTSTP (ORCPT ); Thu, 20 Feb 2014 13:19:15 -0500 Received: from smtp.citrix.com ([66.165.176.89]:62266 "EHLO SMTP.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755815AbaBTSTN (ORCPT ); Thu, 20 Feb 2014 13:19:13 -0500 X-IronPort-AV: E=Sophos;i="4.97,513,1389744000"; d="scan'208";a="104424703" Message-ID: <5306471D.1080809@citrix.com> Date: Thu, 20 Feb 2014 18:19:09 +0000 From: David Vrabel User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.16) Gecko/20121215 Iceowl/1.0b1 Icedove/3.0.11 MIME-Version: 1.0 To: Stefano Stabellini CC: Zoltan Kiss , Konrad Rzeszutek Wilk , Boris Ostrovsky , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , , , , =?ISO-8859-1?Q?Roger_Pau_Monn=E9?= , Jan Beulich , Ian Campbell Subject: Re: [PATCH v9] xen/grant-table: Avoid m2p_override during mapping References: <1392238453-26147-1-git-send-email-zoltan.kiss@citrix.com> <5301F74E.3070107@citrix.com> <53063D2B.1040502@citrix.com> In-Reply-To: Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.80.2.76] X-DLP: MIA2 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. David -- 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/