linux-kernel - Re: [PATCH 3/3] s390/mm: Define arch_get_mappable

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Message-ID: <401e72a7-7865-455a-4c7f-79278e3f0af0@arm.com>
Date:   Thu, 17 Dec 2020 17:15:05 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     David Hildenbrand <david@...hat.com>,
        Heiko Carstens <hca@...ux.ibm.com>
Cc:     linux-mm@...ck.org, akpm@...ux-foundation.org,
        catalin.marinas@....com, linux-arm-kernel@...ts.infradead.org,
        linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Will Deacon <will@...nel.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH 3/3] s390/mm: Define arch_get_mappable_range()



On 12/10/20 12:34 PM, David Hildenbrand wrote:
> 
>> Am 10.12.2020 um 07:58 schrieb Heiko Carstens <hca@...ux.ibm.com>:
>>
>> On Thu, Dec 10, 2020 at 09:48:11AM +0530, Anshuman Khandual wrote:
>>>>> Alternatively leaving __segment_load() and vmem_add_memory() unchanged
>>>>> 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 hotplug
>>>>> paths, which is not optimal.
>>>>
>>>> Ah, sorry. I didn't follow this discussion too closely. I just thought
>>>> my point of view would be clear: let's not have two different ways 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 with
>>> and without memory hotplug enabled. There will be just a single place
>>> i.e vmem_get_max_addr() to update in case the maximum address changes
>>> from VMEM_MAX_PHYS to something else later.
>>
>> Still not. That's way too much code churn for what you want to achieve.
>> If the s390 specific patch would look like below you can add
>>
>> Acked-by: Heiko Carstens <hca@...ux.ibm.com>
>>
>> But please make sure that the arch_get_mappable_range() prototype in
>> 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 size,
>>    if (WARN_ON_ONCE(params->pgprot.pgprot != PAGE_KERNEL.pgprot))
>>        return -EINVAL;
>>
>> +    VM_BUG_ON(!memhp_range_allowed(start, size, 1));
>>    rc = 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 <heiko.carstens@...ibm.com>
>>  */
>>
>> +#include <linux/memory_hotplug.h>
>> #include <linux/memblock.h>
>> #include <linux/pfn.h>
>> #include <linux/mm.h>
>> @@ -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 = 0;
>> +    range.end = 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 = 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() would be sufficient for my use case (virtio-mem).

Hello David,

Quick question. Currently memhp_get_pluggable_range() is a mm/memory_hotplug.c
internal static inline function. Only memhp_range_allowed() is available via
the header include/linux/memory_hotplug.h But For memhp_get_pluggable_range()
to be visible to the drivers, it needs to get included in the header and also
be exported via EXPORT_SYMBOL_GPL() in mm/memory_hotplug.c OR just move the
entire definition as static inline into the header itself. Wondering which way
would be better ?

- Anshuman