linux-kernel - Re: [PATCH V12 1/2] arm64/mm: Hold memory hotplug lock while walking for kernel page table dump

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Date:   Tue, 21 Jan 2020 12:02:41 +0000
From:   Catalin Marinas <Catalin.Marinas@....com>
To:     Anshuman Khandual <Anshuman.Khandual@....com>
CC:     "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "will@...nel.org" <will@...nel.org>,
        Mark Rutland <Mark.Rutland@....com>,
        "david@...hat.com" <david@...hat.com>, "cai@....pw" <cai@....pw>,
        "logang@...tatee.com" <logang@...tatee.com>,
        "cpandya@...eaurora.org" <cpandya@...eaurora.org>,
        "arunks@...eaurora.org" <arunks@...eaurora.org>,
        "dan.j.williams@...el.com" <dan.j.williams@...el.com>,
        "mgorman@...hsingularity.net" <mgorman@...hsingularity.net>,
        "osalvador@...e.de" <osalvador@...e.de>,
        Ard Biesheuvel <Ard.Biesheuvel@....com>,
        Steve Capper <Steve.Capper@....com>,
        "broonie@...nel.org" <broonie@...nel.org>,
        Valentin Schneider <Valentin.Schneider@....com>,
        Robin Murphy <Robin.Murphy@....com>,
        Steven Price <Steven.Price@....com>,
        Suzuki Poulose <Suzuki.Poulose@....com>,
        "ira.weiny@...el.com" <ira.weiny@...el.com>
Subject: Re: [PATCH V12 1/2] arm64/mm: Hold memory hotplug lock while walking
 for kernel page table dump

On Thu, Jan 16, 2020 at 12:15:34PM +0530, Anshuman Khandual wrote:
> The arm64 page table dump code can race with concurrent modification of the
> kernel page tables. When a leaf entries are modified concurrently, the dump
> code may log stale or inconsistent information for a VA range, but this is
> otherwise not harmful.
>
> When intermediate levels of table are freed, the dump code will continue to
> use memory which has been freed and potentially reallocated for another
> purpose. In such cases, the dump code may dereference bogus addresses,
> leading to a number of potential problems.
>
> Intermediate levels of table may by freed during memory hot-remove,
> which will be enabled by a subsequent patch. To avoid racing with
> this, take the memory hotplug lock when walking the kernel page table.
>
> Acked-by: David Hildenbrand <david@...hat.com>
> Acked-by: Mark Rutland <mark.rutland@....com>
> Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>

Acked-by: Catalin Marinas <catalin.marinas@....com>
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IMPORTANT NOTICE: The contents of this email and any attachments are confidential and may also be privileged. If you are not the intended recipient, please notify the sender immediately and do not disclose the contents to any other person, use it for any purpose, or store or copy the information in any medium. Thank you.