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Thu, 3 Dec 2020 12:01:04 +0000 (UTC) Received: from [10.36.113.250] (ovpn-113-250.ams2.redhat.com [10.36.113.250]) by smtp.corp.redhat.com (Postfix) with ESMTP id 58E7B27C40; Thu, 3 Dec 2020 12:01:02 +0000 (UTC) Subject: Re: [RFC V2 3/3] s390/mm: Define arch_get_mappable_range() To: Heiko Carstens , Anshuman Khandual 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> From: David Hildenbrand Organization: Red Hat GmbH Message-ID: <4d6c9ec4-f1be-46b9-5d67-5c53f5afedc5@redhat.com> Date: Thu, 3 Dec 2020 13:01:01 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.4.0 MIME-Version: 1.0 In-Reply-To: <20201203115133.GB9994@osiris> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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. -- Thanks, David / dhildenb