Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755557AbaBTS2Q (ORCPT ); Thu, 20 Feb 2014 13:28:16 -0500 Received: from smtp.citrix.com ([66.165.176.89]:22338 "EHLO SMTP.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754165AbaBTS2M (ORCPT ); Thu, 20 Feb 2014 13:28:12 -0500 X-IronPort-AV: E=Sophos;i="4.97,513,1389744000"; d="scan'208";a="104427444" Message-ID: <53064939.5070103@citrix.com> Date: Thu, 20 Feb 2014 18:28:09 +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> <5306471D.1080809@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 18:26, Stefano Stabellini wrote: > 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. Ok. That would work. 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/