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

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Message-ID: <691872bb-b251-83e0-126e-afd54683c83e@redhat.com>
Date:   Tue, 19 Jan 2021 13:21:53 +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 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().

Apart from that looks good to me.

-- 
Thanks,

David / dhildenb