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Subject: Re: [PATCH V6 3/3] arm64/mm: Enable memory hot remove
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From:   Anshuman Khandual <anshuman.khandual@arm.com>
Message-ID: <bc46b390-01b8-e818-588d-f973dc2c5140@arm.com>
Date:   Fri, 21 Jun 2019 18:23:22 +0530
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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.