linux-kernel - Re: [PATCH V3 1/3] mm/memory_hotplug: Prevalidate the address range being added with platform

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Date:   Wed, 20 Jan 2021 11:41:53 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Anshuman Khandual <anshuman.khandual@....com>, linux-mm@...ck.org,
        akpm@...ux-foundation.org, hca@...ux.ibm.com,
        catalin.marinas@....com
Cc:     Oscar Salvador <osalvador@...e.de>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Will Deacon <will@...nel.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V3 1/3] mm/memory_hotplug: Prevalidate the address range
 being added with platform

On 20.01.21 09:33, Anshuman Khandual wrote:
> 
> 
> On 1/19/21 5:51 PM, David Hildenbrand wrote:
>> On 18.01.21 14:12, 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
>>
>> In this patch, you keep the __add_pages() checks. But as discussed, we
>> could perform it in mm/memremap.c:pagemap_range() insted and convert it
>> to a VM_BUG_ON().
> 
> Just to be sure, will the following change achieve what you are
> suggesting here. pagemap_range() after this change, will again
> be the same like the V1 series.

Yeah, as we used to have in v1. Maybe other reviewers (@Oscar?) have a
different opinion.

If you decide to leave as-is, please fixup the patch description. Thanks!

-- 
Thanks,

David / dhildenb