linux-kernel - Re: [PATCH 2/2] arm64: allow hotpluggable sections to be offlined

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Date:   Sat, 17 Oct 2020 09:34:02 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Sudarshan Rajagopalan <sudaraja@...eaurora.org>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Mark Rutland <mark.rutland@....com>,
        Gavin Shan <gshan@...hat.com>,
        Logan Gunthorpe <logang@...tatee.com>,
        David Hildenbrand <david@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Steven Price <steven.price@....com>,
        Suren Baghdasaryan <surenb@...gle.com>
Subject: Re: [PATCH 2/2] arm64: allow hotpluggable sections to be offlined


> Am 17.10.2020 um 04:03 schrieb Sudarshan Rajagopalan <sudaraja@...eaurora.org>:
> 
> On receiving the MEM_GOING_OFFLINE notification, we disallow offlining of
> any boot memory by checking if section_early or not. With the introduction
> of SECTION_MARK_HOTPLUGGABLE, allow boot mem sections that are marked as
> hotpluggable with this bit set to be offlined and removed. This now allows
> certain boot mem sections to be offlined.
> 

The check (notifier) is in arm64 code. I don‘t see why you cannot make such decisions completely in arm64 code? Why would you have to mark sections?

Also, I think I am missing from *where* the code that marks sections removable is even called? Who makes such decisions?

This feels wrong. 

> Signed-off-by: Sudarshan Rajagopalan <sudaraja@...eaurora.org>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Will Deacon <will@...nel.org>
> Cc: Anshuman Khandual <anshuman.khandual@....com>
> Cc: Mark Rutland <mark.rutland@....com>
> Cc: Gavin Shan <gshan@...hat.com>
> Cc: Logan Gunthorpe <logang@...tatee.com>
> Cc: David Hildenbrand <david@...hat.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Steven Price <steven.price@....com>
> Cc: Suren Baghdasaryan <surenb@...gle.com>
> ---
> arch/arm64/mm/mmu.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index 75df62fea1b6..fb8878698672 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -1487,7 +1487,7 @@ static int prevent_bootmem_remove_notifier(struct notifier_block *nb,
> 
>    for (; pfn < end_pfn; pfn += PAGES_PER_SECTION) {
>        ms = __pfn_to_section(pfn);
> -        if (early_section(ms))
> +        if (early_section(ms) && !removable_section(ms))
>            return NOTIFY_BAD;
>    }
>    return NOTIFY_OK;
> -- 
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
> a Linux Foundation Collaborative Project
>