m68k/mm: Adjust VM area to be unmapped by gap size for __iounmap()

m68k/mm: Adjust VM area to be unmapped by gap size for __iounmap()

commit 3f90f9ef2dda316d64e420d5d51ba369587ccc55 upstream.

If 020/030 support is enabled, get_io_area() leaves an IO_SIZE gap
between mappings which is added to the vm_struct representing the
mapping.  __ioremap() uses the actual requested size (after alignment),
while __iounmap() is passed the size from the vm_struct.

On 020/030, early termination descriptors are used to set up mappings of
extent 'size', which are validated on unmapping. The unmapped gap of
size IO_SIZE defeats the sanity check of the pmd tables, causing
__iounmap() to loop forever on 030.

On 040/060, unmapping of page table entries does not check for a valid
mapping, so the umapping loop always completes there.

Adjust size to be unmapped by the gap that had been added in the
vm_struct prior.

This fixes the hang in atari_platform_init() reported a long time ago,
and a similar one reported by Finn recently (addressed by removing
ioremap() use from the SWIM driver.

Tested on my Falcon in 030 mode - untested but should work the same on
040/060 (the extra page tables cleared there would never have been set
up anyway).

Signed-off-by: Michael Schmitz <schmitzmic@gmail.com>
[geert: Minor commit description improvements]
[geert: This was fixed in 2.4.23, but not in 2.5.x]
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>