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From: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Date: Mon, 5 Dec 2016 15:42:14 +0000
Message-ID: <CAKv+Gu9AVVPp+UM5pCeYCt4HE-Azijp0iUf0QZv6YKFgAuckYw@mail.gmail.com>
Subject: Re: [PATCH 0/2] Hibernate fixes for 'Fix memmap to be initialized for
 the entire section'
To: James Morse <james.morse@arm.com>
Cc: "linux-arm-kernel@lists.infradead.org" 
        <linux-arm-kernel@lists.infradead.org>,
        Robert Richter <rrichter@cavium.com>,
        Will Deacon <will.deacon@arm.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        David Daney <david.daney@cavium.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Hanjun Guo <hanjun.guo@linaro.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
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On 2 December 2016 at 14:49, James Morse <james.morse@arm.com> wrote:
> Patch "arm64: mm: Fix memmap to be initialized for the entire section"
> changes pfn_valid() in a way that breaks hibernate. These patches fix
> hibernate, and provided struct page's are allocated for nomap pages,
> can be applied before [0].
>
> Hibernate core code belives 'valid' to mean "I can access this". It
> uses pfn_valid() to test the page if the page is 'valid'.
>
> pfn_valid() needs to be changed so that all struct pages in a numa
> node have the same node-id. Currently 'nomap' pages are skipped, and
> retain their pre-numa node-ids, which leads to a later BUG_ON().
>
> These patches make hibernate's savable_page() take its escape route
> via 'if (PageReserved(page) && pfn_is_nosave(pfn))'.
>

This makes me feel slightly uneasy. Robert makes a convincing point,
but I wonder if we can expect more fallout from the ambiguity of
pfn_valid(). Now we are not only forced to assign non-existing (as far
as the OS is concerned) pages to the correct NUMA node, we also need
to set certain page flags.