[PATCH 3/6] ARM: mm: Drop the lowmem watermark check from virt_addr_valid()

[Russell King - ARM Linux]

On Thu, Nov 14, 2013 at 02:37:43PM -0500, Santosh Shilimkar wrote:
> Slab allocator can allocate memory beyond the lowmem watermark
> which can lead to false failure of virt_addr_valid().

This is definitely going to cause problems.

> So drop the check. The issue was seen with percpu_alloc()
> in KVM code which was allocating memory beyond lowmem watermark.
> 
> Am not completly sure whether this is the right fix and if it could
> impact any other user of virt_addr_valid(). Without this fix as
> pointed out the KVM init was failing in my testing.

virt_addr_valid() gets used in some places to check whether the virtual
address is part of the lowmem mapping and explicitly not part of vmalloc()
or DMA coherent space:

drivers/mtd/nand/gpmi-nand/gpmi-nand.c
drivers/net/wireless/ath/ath6kl/sdio.c

It opens up the checks in include/linux/scatterlist.h to start accepting
non-streaming DMA capable buffers as well.

It also bypasses a check in the slab code to ensure that it's a potentially
valid pointer that was handed out by slab.

.. etc ..