On Tue, Jul 31, 2012 at 08:50:02PM +0000, Arnd Bergmann wrote:On Tuesday 31 July 2012, Russell King - ARM Linux wrote:I still fail to see how not having highmem enabled would ever cause memory
corruption errors (unless something dealing with memory in a very very
wrong way - iow, not using one of the reservation or memory allocation
methods provided by the kernel.)
The problem is that all users of ux500 systems pass a command line like
vmalloc=256M mem=128M@0 mali.mali_mem=32M@128M hwmem=168M@160M mem=48M@328M mem_issw=1M@383M mem=640M@384M
This is of course totally bogus and should not be done. If I understand
Lee correctly, one of the issues resulting from passing a command
line like this without enabling highmem is memory corruption.
But the question is _why_ does that corruption happen.
From the above, we will end up with the kernel getting:
0x00000000 - 0x07ffffff (128M @ 0)
0x14800000 - 0x177fffff (48M @ 328M)
0x18000000 - 0x3fffffff (640M @ 384M)
with:
0x08000000 - 0x081fffff used for mali
0x0a000000 - 0x147fffff used for hwmem
0x17f00000 - 0x17ffffff used for mem_issw
Now, with highmem disabled, the kernel should still map exactly the
regions: 0x00000000 - 0x07ffffff, 0x14800000 - 0x177fffff, into the
direct mapped region, and truncate the 0x18000000 - 0x3fffffff
region appropriately, reducing the amount of memory available such
that it won't overlap the vmalloc area (which you've specified to be
a minimum of 256M.)
This should _NOT_ cause any memory corruption.
So, come on guys. Debugging is *mandatory* for this kind of problem.
Papering over it is obscene.