linux-kernel - Re: [PATCH V6 3/3] arm64/mm: Enable memory hot remove

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Message-ID: <bc46b390-01b8-e818-588d-f973dc2c5140@arm.com>
Date:   Fri, 21 Jun 2019 18:23:22 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, akpm@...ux-foundation.org,
        catalin.marinas@....com, will.deacon@....com
Cc:     mark.rutland@....com, mhocko@...e.com, ira.weiny@...el.com,
        david@...hat.com, cai@....pw, logang@...tatee.com,
        james.morse@....com, cpandya@...eaurora.org, arunks@...eaurora.org,
        dan.j.williams@...el.com, mgorman@...hsingularity.net,
        osalvador@...e.de, ard.biesheuvel@....com, steve.capper@....com
Subject: Re: [PATCH V6 3/3] arm64/mm: Enable memory hot remove


On 06/19/2019 09:47 AM, Anshuman Khandual wrote:
> +#ifdef CONFIG_MEMORY_HOTPLUG
> +	/*
> +	 * FIXME: We should have called remove_pagetable(start, end, true).
> +	 * vmemmap and vmalloc virtual range might share intermediate kernel
> +	 * page table entries. Removing vmemmap range page table pages here
> +	 * can potentially conflict with a cuncurrent vmalloc() allocation.
> +	 *
> +	 * This is primarily because valloc() does not take init_mm ptl for
> +	 * the entire page table walk and it's modification. Instead it just
> +	 * takes the lock while allocating and installing page table pages
> +	 * via [p4d|pud|pmd|pte]_aloc(). A cuncurrently vanishing page table
> +	 * entry via memory hotremove can cause vmalloc() kernel page table
> +	 * walk pointers to be invalid on the fly which can cause corruption
> +	 * or worst, a crash.

There are couple of typos above which I will fix along with other reviews.