From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-10.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 70C18C433FE for ; Tue, 8 Dec 2020 05:33:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 224A723A60 for ; Tue, 8 Dec 2020 05:33:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726825AbgLHFc6 (ORCPT ); Tue, 8 Dec 2020 00:32:58 -0500 Received: from foss.arm.com ([217.140.110.172]:41792 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726068AbgLHFc5 (ORCPT ); Tue, 8 Dec 2020 00:32:57 -0500 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id B38741FB; Mon, 7 Dec 2020 21:32:11 -0800 (PST) Received: from [10.163.87.7] (unknown [10.163.87.7]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id D80663F718; Mon, 7 Dec 2020 21:32:08 -0800 (PST) Subject: Re: [RFC V2 3/3] s390/mm: Define arch_get_mappable_range() To: David Hildenbrand , Heiko Carstens Cc: linux-mm@kvack.org, akpm@linux-foundation.org, linux-arm-kernel@lists.infradead.org, linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, Vasily Gorbik References: <1606706992-26656-1-git-send-email-anshuman.khandual@arm.com> <1606706992-26656-4-git-send-email-anshuman.khandual@arm.com> <20201202203233.GB11274@osiris> <24905c32-f6c1-97a0-000f-f822b9870ea5@arm.com> <20201203115133.GB9994@osiris> <4d6c9ec4-f1be-46b9-5d67-5c53f5afedc5@redhat.com> <62c60c9e-20d6-25bd-94d0-78bfed0f2476@arm.com> <02dfe6f5-efb6-c04d-c34a-a1e7393625cf@redhat.com> From: Anshuman Khandual Message-ID: <9e80ad53-d203-d7d2-3fc8-92fa860bc869@arm.com> Date: Tue, 8 Dec 2020 11:02:09 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <02dfe6f5-efb6-c04d-c34a-a1e7393625cf@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/7/20 2:33 PM, David Hildenbrand wrote: > On 07.12.20 05:38, Anshuman Khandual wrote: >> >> >> On 12/3/20 5:31 PM, David Hildenbrand wrote: >>> On 03.12.20 12:51, Heiko Carstens wrote: >>>> On Thu, Dec 03, 2020 at 06:03:00AM +0530, Anshuman Khandual wrote: >>>>>>> diff --git a/arch/s390/mm/extmem.c b/arch/s390/mm/extmem.c >>>>>>> index 5060956b8e7d..cc055a78f7b6 100644 >>>>>>> --- a/arch/s390/mm/extmem.c >>>>>>> +++ b/arch/s390/mm/extmem.c >>>>>>> @@ -337,6 +337,11 @@ __segment_load (char *name, int do_nonshared, unsigned long *addr, unsigned long >>>>>>> goto out_free_resource; >>>>>>> } >>>>>>> >>>>>>> + if (seg->end + 1 > VMEM_MAX_PHYS || seg->end + 1 < seg->start_addr) { >>>>>>> + rc = -ERANGE; >>>>>>> + goto out_resource; >>>>>>> + } >>>>>>> + >>>>>>> rc = vmem_add_mapping(seg->start_addr, seg->end - seg->start_addr + 1); >>>>>>> if (rc) >>>>>>> goto out_resource; >>>>>>> diff --git a/arch/s390/mm/vmem.c b/arch/s390/mm/vmem.c >>>>>>> index b239f2ba93b0..06dddcc0ce06 100644 >>>>>>> --- a/arch/s390/mm/vmem.c >>>>>>> +++ b/arch/s390/mm/vmem.c >>>>>>> @@ -532,14 +532,19 @@ void vmem_remove_mapping(unsigned long start, unsigned long size) >>>>>>> mutex_unlock(&vmem_mutex); >>>>>>> } >>>>>>> >>>>>>> +struct range arch_get_mappable_range(void) >>>>>>> +{ >>>>>>> + struct range memhp_range; >>>>>>> + >>>>>>> + memhp_range.start = 0; >>>>>>> + memhp_range.end = VMEM_MAX_PHYS; >>>>>>> + return memhp_range; >>>>>>> +} >>>>>>> + >>>>>>> int vmem_add_mapping(unsigned long start, unsigned long size) >>>>>>> { >>>>>>> int ret; >>>>>>> >>>>>>> - if (start + size > VMEM_MAX_PHYS || >>>>>>> - start + size < start) >>>>>>> - return -ERANGE; >>>>>>> - >>>>>> >>>>>> I really fail to see how this could be considered an improvement for >>>>>> s390. Especially I do not like that the (central) range check is now >>>>>> moved to the caller (__segment_load). Which would mean potential >>>>>> additional future callers would have to duplicate that code as well. >>>>> >>>>> The physical range check is being moved to the generic hotplug code >>>>> via arch_get_mappable_range() instead, making the existing check in >>>>> vmem_add_mapping() redundant. Dropping the check there necessitates >>>>> adding back a similar check in __segment_load(). Otherwise there >>>>> will be a loss of functionality in terms of range check. >>>>> >>>>> May be we could just keep this existing check in vmem_add_mapping() >>>>> as well in order avoid this movement but then it would be redundant >>>>> check in every hotplug path. >>>>> >>>>> So I guess the choice is to either have redundant range checks in >>>>> all hotplug paths or future internal callers of vmem_add_mapping() >>>>> take care of the range check. >>>> >>>> The problem I have with this current approach from an architecture >>>> perspective: we end up having two completely different methods which >>>> are doing the same and must be kept in sync. This might be obvious >>>> looking at this patch, but I'm sure this will go out-of-sync (aka >>>> broken) sooner or later. >>> >>> Exactly, there should be one function only that was the whole idea of >>> arch_get_mappable_range(). >>> >>>> >>>> Therefore I would really like to see a single method to do the range >>>> checking. Maybe you could add a callback into architecture code, so >>>> that such an architecture specific function could also be used >>>> elsewhere. Dunno. >>>> >>> >>> I think we can just switch to using "memhp_range_allowed()" here then >>> after implementing arch_get_mappable_range(). >>> >>> Doesn't hurt to double check in vmem_add_mapping() - especially to keep >>> extmem working without changes. At least for callers of memory hotplug >>> it's then clear which values actually won't fail deep down in arch code. >> >> But there is a small problem here. memhp_range_allowed() is now defined >> and available with CONFIG_MEMORY_HOTPLUG where as vmem_add_mapping() and >> __segment_load() are generally available without any config dependency. >> So if CONFIG_MEMORY_HOTPLUG is not enabled there will be a build failure >> in vmem_add_mapping() for memhp_range_allowed() symbol. >> >> We could just move VM_BUG_ON(!memhp_range_allowed(start, size, 1)) check >> from vmem_add_mapping() to arch_add_memory() like on arm64 platform. But >> then __segment_load() would need that additional new check to compensate >> as proposed earlier. >> >> Also leaving vmem_add_mapping() and __segment_load() unchanged will cause >> the address range check to be called three times on the hotplug path i.e >> >> 1. register_memory_resource() >> 2. arch_add_memory() >> 3. vmem_add_mapping() >> >> Moving memhp_range_allowed() check inside arch_add_memory() seems better >> and consistent with arm64. Also in the future, any platform which choose >> to override arch_get_mappable() will have this additional VM_BUG_ON() in >> their arch_add_memory(). > > Yeah, it might not make sense to add these checks all over the place. > The important part is that > > 1. There is a check somewhere (and if it's deep down in arch code) > 2. There is an obvious way for callers to find out what valid values are. > > > I guess it would be good enough to > > a) Factor out getting arch ranges into arch_get_mappable_range() > b) Provide memhp_get_pluggable_range() Have posted V1 earlier in the day which hopefully accommodates all previous suggestions but otherwise do let me know if anything else still needs to be improved upon. https://lore.kernel.org/linux-mm/1607400978-31595-1-git-send-email-anshuman.khandual@arm.com/ > > Both changes only make sense with an in-tree user. I'm planning on using > this functionality in virtio-mem code. I can pickup your patches, drop > the superfluous checks, and use it from virtio-mem code. Makese sense > (BTW, looks like we'll see aarch64 support for virtio-mem soon)? I have not been following virtio-mem closely. But is there something pending on arm64 platform which prevents virtio-mem enablement ?