linux-kernel - arm64: mm: update max_pfn after memory hotplug

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Message-ID: <cover.1632853776.git.quic_cgoldswo@quicinc.com>
Date:   Tue, 28 Sep 2021 11:51:48 -0700
From:   Chris Goldsworthy <quic_cgoldswo@...cinc.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
CC:     David Hildenbrand <david@...hat.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        "Sudarshan Rajagopalan" <quic_sudaraja@...cinc.com>,
        Georgi Djakov <quic_c_gdjako@...cinc.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
        Chris Goldsworthy <quic_cgoldswo@...cinc.com>
Subject: arm64: mm: update max_pfn after memory hotplug

Follow up of RFC patch:

https://lore.kernel.org/linux-mm/a3bf84c4-8f35-f273-145c-55928a06f332@quicinc.com/T/#m219937b1acdd40318bbe90ab39f187804775eb74

On arm64 we set max_pfn at boot in arch/arm64/mm/init.c. If you
hotplug in memory after booting up, max_pfn is not updated. This
breaks diagnostic functions executed from user space like
read_page_owner():

https://elixir.bootlin.com/linux/v5.14.7/source/mm/page_owner.c#L472

or kpageflags_read() (see how get_max_dump_pfn() is used):

https://elixir.bootlin.com/linux/v5.14.7/source/fs/proc/page.c#L47

Thus, this patch updates max_pfn and max_low_pfn in arm64's
arch_add_memory() function, mirroring what is updatated during boot:

https://elixir.bootlin.com/linux/v5.14.7/source/arch/arm64/mm/init.c#L448

Quick reference for David's Acked-by, with a follow-up discussion on
max_low_pfn:

https://lore.kernel.org/linux-mm/a3bf84c4-8f35-f273-145c-55928a06f332@quicinc.com/T/#m7d30b3afa632a4fa836f5fe55f4ee8e7bbc83e5d
https://lore.kernel.org/linux-mm/a3bf84c4-8f35-f273-145c-55928a06f332@quicinc.com/T/#m0d0e509375af1504d25451d079c5cbd6e7aa513b

Sudarshan Rajagopalan (1):
  arm64: mm: update max_pfn after memory hotplug

 arch/arm64/mm/mmu.c | 5 +++++
 1 file changed, 5 insertions(+)

-- 
2.7.4