linux-kernel - Re: [PATCH 2/2] of/fdt: Make sure no-map does not remove already reserved regions

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Message-ID: <20210115173015.GA1496104@robh.at.kernel.org>
Date:   Fri, 15 Jan 2021 11:30:15 -0600
From:   Rob Herring <robh@...nel.org>
To:     Quentin Perret <qperret@...gle.com>
Cc:     robh+dt@...nel.org, drinkcat@...omium.org,
        devicetree@...r.kernel.org, f.fainelli@...il.com,
        swboyd@...omium.org, karahmed@...zon.de, kernel-team@...roid.com,
        frowand.list@...il.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] of/fdt: Make sure no-map does not remove already
 reserved regions

On Fri, 15 Jan 2021 11:45:44 +0000, Quentin Perret wrote:
> From: Nicolas Boichat <drinkcat@...omium.org>
> 
> If the device tree is incorrectly configured, and attempts to
> define a "no-map" reserved memory that overlaps with the kernel
> data/code, the kernel would crash quickly after boot, with no
> obvious clue about the nature of the issue.
> 
> For example, this would happen if we have the kernel mapped at
> these addresses (from /proc/iomem):
> 40000000-41ffffff : System RAM
>   40080000-40dfffff : Kernel code
>   40e00000-411fffff : reserved
>   41200000-413e0fff : Kernel data
> 
> And we declare a no-map shared-dma-pool region at a fixed address
> within that range:
> mem_reserved: mem_region {
> 	compatible = "shared-dma-pool";
> 	reg = <0 0x40000000 0 0x01A00000>;
> 	no-map;
> };
> 
> To fix this, when removing memory regions at early boot (which is
> what "no-map" regions do), we need to make sure that the memory
> is not already reserved. If we do, __reserved_mem_reserve_reg
> will throw an error:
> [    0.000000] OF: fdt: Reserved memory: failed to reserve memory
>    for node 'mem_region': base 0x0000000040000000, size 26 MiB
> and the code that will try to use the region should also fail,
> later on.
> 
> We do not do anything for non-"no-map" regions, as memblock
> explicitly allows reserved regions to overlap, and the commit
> that this fixes removed the check for that precise reason.
> 
> [ qperret: fixed conflicts caused by the usage of memblock_mark_nomap ]
> 
> Fixes: 094cb98179f19b7 ("of/fdt: memblock_reserve /memreserve/ regions in the case of partial overlap")
> Signed-off-by: Nicolas Boichat <drinkcat@...omium.org>
> Reviewed-by: Stephen Boyd <swboyd@...omium.org>
> Signed-off-by: Quentin Perret <qperret@...gle.com>
> ---
>  drivers/of/fdt.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 

Applied, thanks!