linux-kernel - Re: [PATCH 2/3] Documentation: riscv: Add documentation that describes the VM layout

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Message-ID: <7d9036d9-488b-47cc-4673-1b10c11baad0@ghiti.fr>
Date:   Thu, 25 Feb 2021 06:56:11 -0500
From:   Alex Ghiti <alex@...ti.fr>
To:     David Hildenbrand <david@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Arnd Bergmann <arnd@...db.de>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>, linux-doc@...r.kernel.org,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kasan-dev@...glegroups.com, linux-arch@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH 2/3] Documentation: riscv: Add documentation that
 describes the VM layout

Le 2/25/21 à 5:34 AM, David Hildenbrand a écrit :
>                   |            |                  |         |> + 
> ffffffc000000000 | -256    GB | ffffffc7ffffffff |   32 GB | kasan
>> +   ffffffcefee00000 | -196    GB | ffffffcefeffffff |    2 MB | fixmap
>> +   ffffffceff000000 | -196    GB | ffffffceffffffff |   16 MB | PCI io
>> +   ffffffcf00000000 | -196    GB | ffffffcfffffffff |    4 GB | vmemmap
>> +   ffffffd000000000 | -192    GB | ffffffdfffffffff |   64 GB | 
>> vmalloc/ioremap space
>> +   ffffffe000000000 | -128    GB | ffffffff7fffffff |  126 GB | 
>> direct mapping of all physical memory
> 
> ^ So you could never ever have more than 126 GB, correct?
> 
> I assume that's nothing new.
> 

Before this patch, the limit was 128GB, so in my sense, there is nothing 
new. If ever we want to increase that limit, we'll just have to lower 
PAGE_OFFSET, there is still some unused virtual addresses after kasan 
for example.

Thanks,

Alex