linux-kernel - Re: [PATCH v3] drivers/char: kmem: disable on arm64

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Message-ID: <CAKv+Gu-qXZXVV7MX-oB76dK21RGXEpc=P4vE6MF2nMA+_Q=LtQ@mail.gmail.com>
Date:   Mon, 17 Jul 2017 18:04:57 +0100
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
Cc:     "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Will Deacon <will.deacon@....com>,
        Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH v3] drivers/char: kmem: disable on arm64

On 17 July 2017 at 15:18, gregkh@...uxfoundation.org
<gregkh@...uxfoundation.org> wrote:
> On Tue, Jun 20, 2017 at 01:20:49PM +0200, Ard Biesheuvel wrote:
>> On 20 June 2017 at 08:59, Ard Biesheuvel <ard.biesheuvel@...aro.org> wrote:
>> > As it turns out, arm64 deviates from other architectures in the way it
>> > maps the VMALLOC region: on most (all?) other architectures, it resides
>> > strictly above the kernel's direct mapping of DRAM, but on arm64, this
>> > is the other way around. For instance, for a 48-bit VA configuration,
>> > we have
>> >
>> >   modules : 0xffff000000000000 - 0xffff000008000000   (   128 MB)
>> >   vmalloc : 0xffff000008000000 - 0xffff7dffbfff0000   (129022 GB)
>> >   ...
>> >   vmemmap : 0xffff7e0000000000 - 0xffff800000000000   (  2048 GB maximum)
>> >             0xffff7e0000000000 - 0xffff7e0003ff0000   (    63 MB actual)
>> >   memory  : 0xffff800000000000 - 0xffff8000ffc00000   (  4092 MB)
>> >
>> > This has mostly gone unnoticed until now, but it does appear that it
>> > breaks an assumption in the kcore
>>
>> s/kcore/kmem/
>
> v4?  :)
>

This is already in mainline as 06c35ef1fdf8d955684448683f7e48ac5f15ccfd