[U-Boot] [PATCH] lib: lmb: fix overflow in __lmb_alloc_base w/ large RAM

[Stephen Warren <swarren@wwwdotorg.org>]

On 07/31/2014 01:40 PM, Stephen Warren wrote:
> From: Stephen Warren <swarren@nvidia.com>
>
> If a 32-bit system has 2GB of RAM, and the base address of that RAM is
> 2GB, then start+size will overflow a 32-bit value (to a value of 0).
>
> __lmb_alloc_base is affected by this; it calculates the minimum of
> (start+size of RAM) and max_addr. However, when start+size is 0, it
> is always less than max_addr, which causes the value of max_addr not
> to be taken into account when restricting the allocation's location.
>
> Fix this by calculating start+size separately, and if that calculation
> underflows, using -1 (interpreted as the max unsigned value) as the
> value instead, and then taking the min of that and max_addr. Now that
> start+size doesn't overflow, it's typically large, and max_addr
> dominates the min() call, and is taken into account.
>
> The user-visible symptom of this bug is that CONFIG_BOOTMAP_SZ is ignored
> on Tegra124 systems with 2GB of RAM, which in turn causes the DT to be
> relocated at the very end of RAM, which the ARM Linux kernel doesn't map
> during early boot, and which causes boot failures. With this fix,
> CONFIG_BOOTMAP_SZ correctly restricts the relocated DT to a much lower
> address, and everything works.

TomR,

Does this patch look OK to you? I imagine that TomW is holding off 
applying "ARM: tegra: Use mem size from MC rather than ODMDATA" since it 
depends on this patch, which isn't applied yet.

Thanks.