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Thu, 10 Dec 2020 09:39:20 +0000 (UTC) Received: from [10.36.113.177] (ovpn-113-177.ams2.redhat.com [10.36.113.177]) by smtp.corp.redhat.com (Postfix) with ESMTP id 6A6D65D6BA; Thu, 10 Dec 2020 09:39:16 +0000 (UTC) Subject: Re: [PATCH 3/3] s390/mm: Define arch_get_mappable_range() To: Anshuman Khandual , Heiko Carstens Cc: linux-mm@kvack.org, akpm@linux-foundation.org, catalin.marinas@arm.com, linux-arm-kernel@lists.infradead.org, linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, Vasily Gorbik , Will Deacon , Ard Biesheuvel , Mark Rutland References: <20201210065845.GA20691@osiris> <0a2f6eb1-c38b-9cc2-5c45-16f6c8999ce2@arm.com> <2a379949-4ecb-e380-560e-78ef91168c87@redhat.com> <1ff0df3a-a6bf-7c1c-6e10-02de3477e3ed@arm.com> From: David Hildenbrand Organization: Red Hat GmbH Message-ID: <36cdf123-5b2e-0bd5-0bd7-82a801cf2e43@redhat.com> Date: Thu, 10 Dec 2020 10:39:15 +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: <1ff0df3a-a6bf-7c1c-6e10-02de3477e3ed@arm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Content-Transfer-Encoding: quoted-printable 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 10.12.20 09:58, Anshuman Khandual wrote: >=20 >=20 > On 12/10/20 1:32 PM, David Hildenbrand wrote: >> On 10.12.20 08:40, Anshuman Khandual wrote: >>> >>> >>> On 12/10/20 12:34 PM, David Hildenbrand wrote: >>>> >>>>> Am 10.12.2020 um 07:58 schrieb Heiko Carstens : >>>>> >>>>> =EF=BB=BFOn Thu, Dec 10, 2020 at 09:48:11AM +0530, Anshuman Khandua= l wrote: >>>>>>>> Alternatively leaving __segment_load() and vmem_add_memory() unc= hanged >>>>>>>> will create three range checks i.e two memhp_range_allowed() and= the >>>>>>>> existing VMEM_MAX_PHYS check in vmem_add_mapping() on all the ho= tplug >>>>>>>> paths, which is not optimal. >>>>>>> >>>>>>> Ah, sorry. I didn't follow this discussion too closely. I just th= ought >>>>>>> my point of view would be clear: let's not have two different way= s to >>>>>>> check for the same thing which must be kept in sync. >>>>>>> Therefore I was wondering why this next version is still doing >>>>>>> that. Please find a way to solve this. >>>>>> >>>>>> The following change is after the current series and should work w= ith >>>>>> and without memory hotplug enabled. There will be just a single pl= ace >>>>>> i.e vmem_get_max_addr() to update in case the maximum address chan= ges >>>>>> from VMEM_MAX_PHYS to something else later. >>>>> >>>>> Still not. That's way too much code churn for what you want to achi= eve. >>>>> If the s390 specific patch would look like below you can add >>>>> >>>>> Acked-by: Heiko Carstens >>>>> >>>>> But please make sure that the arch_get_mappable_range() prototype i= n >>>>> linux/memory_hotplug.h is always visible and does not depend on >>>>> CONFIG_MEMORY_HOTPLUG. I'd like to avoid seeing sparse warnings >>>>> because of this. >>>>> >>>>> Thanks. >>>>> >>>>> diff --git a/arch/s390/mm/init.c b/arch/s390/mm/init.c >>>>> index 77767850d0d0..e0e78234ae57 100644 >>>>> --- a/arch/s390/mm/init.c >>>>> +++ b/arch/s390/mm/init.c >>>>> @@ -291,6 +291,7 @@ int arch_add_memory(int nid, u64 start, u64 siz= e, >>>>> if (WARN_ON_ONCE(params->pgprot.pgprot !=3D PAGE_KERNEL.pgprot)) >>>>> return -EINVAL; >>>>> >>>>> + VM_BUG_ON(!memhp_range_allowed(start, size, 1)); >>>>> rc =3D vmem_add_mapping(start, size); >>>>> if (rc) >>>>> return rc; >>>>> diff --git a/arch/s390/mm/vmem.c b/arch/s390/mm/vmem.c >>>>> index b239f2ba93b0..ccd55e2f97f9 100644 >>>>> --- a/arch/s390/mm/vmem.c >>>>> +++ b/arch/s390/mm/vmem.c >>>>> @@ -4,6 +4,7 @@ >>>>> * Author(s): Heiko Carstens >>>>> */ >>>>> >>>>> +#include >>>>> #include >>>>> #include >>>>> #include >>>>> @@ -532,11 +533,23 @@ void vmem_remove_mapping(unsigned long start,= unsigned long size) >>>>> mutex_unlock(&vmem_mutex); >>>>> } >>>>> >>>>> +struct range arch_get_mappable_range(void) >>>>> +{ >>>>> + struct range range; >>>>> + >>>>> + range.start =3D 0; >>>>> + range.end =3D VMEM_MAX_PHYS; >>>>> + return range; >>>>> +} >>>>> + >>>>> int vmem_add_mapping(unsigned long start, unsigned long size) >>>>> { >>>>> + struct range range; >>>>> int ret; >>>>> >>>>> - if (start + size > VMEM_MAX_PHYS || >>>>> + range =3D arch_get_mappable_range(); >>>>> + if (start < range.start || >>>>> + start + size > range.end || >>>>> start + size < start) >>>>> return -ERANGE; >>>>> >>>>> >>>> >>>> Right, what I had in mind as reply to v1. Not sure if we really need= new checks in common code. Having a new memhp_get_pluggable_range() woul= d be sufficient for my use case (virtio-mem). >>> Didn't quite understand "Not sure if we really need new checks in com= mon code". >>> Could you please be more specific. New checks as in pagemap_range() ?= Because >>> other places it is either replacing erstwhile check_hotplug_memory_ad= dressable() >>> or just moving existing checks from platform arch_add_memory() to the= beginning >>> of various hotplug paths. >> >> The main concern I have with current code is that it makes it impossib= le >> for some driver to detect which ranges it could actually later hotplug= . >> You cannot warn about a strange setup before you actually run into the >> issues while trying to add memory. Like returning "-EINVAL" from a >> function but not exposing which values are actually valid. >> >> If we have memhp_get_pluggable_range(), we have such a mechanism and >> >> 1. Trying to add out-of-range memory will fail (although deep down in >> arch code, but at least it fails). >> >> 2. There is a way for drivers to find out which values are actually >> valid before triggering 1. >=20 > Right, that is an important use case from a driver perspective as it > helps validate the range being attempted for hotplug, before failing. > But then memhp_range_allowed() also uses the same mechanism i.e > memhp_get_pluggable_range() to unify >=20 > 1. Generic check_hotplug_memory_addressable() > 2. Platform checks in arch_add_memory() >=20 > This unified function can be called just at the beginning of memory > hotplug so that both (1) and (2) can be dropped all together. This > is just a logical extension which does improve the memory hotplug > implementation (in itself) by failing earlier and while at it, also > unifying generic and platform specific range constraints. Both the > use cases are orthogonal IMHO. As longs as it simplifies the code sure. But at least in the s390x case, we cannot get rid of the internal checks. --=20 Thanks, David / dhildenb