Re: [PATCH V2 1/3] mm/hotplug: Prevalidate the address range being added with platform

[Anshuman Khandual <anshuman.khandual@arm.com>]

On 1/11/21 4:21 PM, David Hildenbrand wrote:
> On 17.12.20 16:28, Anshuman Khandual wrote:
>> This introduces memhp_range_allowed() which can be called in various memory
>> hotplug paths to prevalidate the address range which is being added, with
>> the platform. Then memhp_range_allowed() calls memhp_get_pluggable_range()
>> which provides applicable address range depending on whether linear mapping
>> is required or not. For ranges that require linear mapping, it calls a new
>> arch callback arch_get_mappable_range() which the platform can override. So
>> the new callback, in turn provides the platform an opportunity to configure
>> acceptable memory hotplug address ranges in case there are constraints.
>>
>> This mechanism will help prevent platform specific errors deep down during
>> hotplug calls. This drops now redundant check_hotplug_memory_addressable()
>> check in __add_pages() but instead adds a VM_BUG_ON() check which would
>> ensure that the range has been validated with memhp_range_allowed() earlier
>> in the call chain. Besides memhp_get_pluggable_range() also can be used by
>> potential memory hotplug callers to avail the allowed physical range which
>> would go through on a given platform.
>>
>> This does not really add any new range check in generic memory hotplug but
>> instead compensates for lost checks in arch_add_memory() where applicable
>> and check_hotplug_memory_addressable(), with unified memhp_range_allowed().
>>
> 
> Subject s/mm\/hotplug/mm\/memory_hotplug/

Sure, will do.

> 
> Everywhere in this patch: Use "true/false" for boolean values.

Sure, will change.

> 
>> Cc: David Hildenbrand <david@redhat.com>
>> Cc: Andrew Morton <akpm@linux-foundation.org>
>> Cc: linux-mm@kvack.org
>> Cc: linux-kernel@vger.kernel.org
>> Suggested-by: David Hildenbrand <david@redhat.com>
>> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
>> ---
>>  include/linux/memory_hotplug.h | 10 +++++
>>  mm/memory_hotplug.c            | 79 +++++++++++++++++++++++++---------
>>  mm/memremap.c                  |  6 +++
>>  3 files changed, 75 insertions(+), 20 deletions(-)
>>
>> diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
>> index 551093b74596..8d72354758c8 100644
>> --- a/include/linux/memory_hotplug.h
>> +++ b/include/linux/memory_hotplug.h
>> @@ -70,6 +70,9 @@ typedef int __bitwise mhp_t;
>>   */
>>  #define MEMHP_MERGE_RESOURCE	((__force mhp_t)BIT(0))
>>  
>> +bool memhp_range_allowed(u64 start, u64 size, bool need_mapping);
>> +struct range memhp_get_pluggable_range(bool need_mapping);
> 
> AFAIKs, all memhp_get_pluggable_range() users pass "1".

Right.

> 
> What about the "add_pages()-only" path?

I had dropped memhp_range_allowed() changes for add_pages() in pagemap_range()
because you had mentioned not to add any new checks in the generic code. Will
add it back if that is preferred.