linux-kernel - Re: [PATCH] Documentation/arm64: add memory layout with 4KB pages + VA39-bit

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Message-ID: <YV3ZfmSHHKSWfDQu@arm.com>
Date:   Wed, 6 Oct 2021 18:14:38 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Jisheng Zhang <Jisheng.Zhang@...aptics.com>
Cc:     Will Deacon <will@...nel.org>, Jonathan Corbet <corbet@....net>,
        linux-arm-kernel@...ts.infradead.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Documentation/arm64: add memory layout with 4KB pages +
 VA39-bit

On Thu, Sep 30, 2021 at 06:50:26PM +0800, Jisheng Zhang wrote:
> The 4KB pages + 3 levels (39-bit) combination is also widely used in
> arm64 world, add the memory layout description for this combination.
> 
> Signed-off-by: Jisheng Zhang <Jisheng.Zhang@...aptics.com>
> ---
>  Documentation/arm64/memory.rst | 17 +++++++++++++++++
>  1 file changed, 17 insertions(+)
> 
> diff --git a/Documentation/arm64/memory.rst b/Documentation/arm64/memory.rst
> index 901cd094f4ec..d1745b570f0c 100644
> --- a/Documentation/arm64/memory.rst
> +++ b/Documentation/arm64/memory.rst
> @@ -26,6 +26,23 @@ The swapper_pg_dir address is written to TTBR1 and never written to
>  TTBR0.
>  
>  
> +AArch64 Linux memory layout with 4KB pages + 3 levels (39-bit)::
> +  Start			End			Size		Use
> +  -----------------------------------------------------------------------
> +  0000000000000000	0000007fffffffff	 512GB		user
> +  ffffff8000000000	ffffffbfffffffff	 256GB		kernel logical memory map
> + [ffffffb000000000	ffffffbfffffffff]	  64GB		[kasan shadow region]
> +  ffffffc000000000	ffffffc007ffffff	 128MB		bpf jit region
> +  ffffffc008000000	ffffffc00fffffff	 128MB		modules
> +  ffffffc010000000	fffffffdefffffff      253440MB		vmalloc
> +  fffffffdf0000000	fffffffdfdffffff	 224MB		fixed mappings (top down)
> +  fffffffdfe000000	fffffffdfe7fffff	   8MB		[guard region]
> +  fffffffdfe800000	fffffffdff7fffff	  16MB		PCI I/O space
> +  fffffffdff800000	fffffffdffffffff	   8MB		[guard region]
> +  fffffffe00000000	ffffffffefffffff	   4GB		vmemmap
> +  ffffffff00000000	ffffffffffffffff	   4GB		[guard region]

I wouldn't bother maintaining these. There are other combinations that
people may use. The 4KB + 48-bit VA is defconfig while 64KB + 52-bit was
more interesting, so we thought it would be useful.

I'm more inclined to remove them altogether and maybe just add some
high-level ascii art as per the log of commit f4693c2716b3 ("arm64: mm:
extend linear region for 52-bit VA configurations").

-- 
Catalin