fix memremap on ARM

Quoted 53 lines · Dan Williams

Quoted 42 lines · Ard Biesheuvel

This is something I ran into while working on support for the UEFI memory attributes and ESRT tables. In both cases, these tables are passed to the kernel in memory which is guaranteed to be below 4 GB, but may be outside of the kernel direct mapping. (UEFI typically attempts to allocate from the top down, which means such tables are highly likely to be in highmem for any system with more than 760 MB of system RAM)

The recently introduced memremap() is a very useful abstraction for accessing such tables, because it is generic, and already attempts to do the right thing with respect to regions that may already have been mapped directly. However, it falls back to ioremap_cache() for mapping high memory, which is not allowed on ARM for system RAM, and also results in the region to be mapped with different attributes depending on whether it is covered by lowmem or not.

So instead, create an arch specific hook 'arch_memremap_wb(), and implement it for ARM using the same memory attributes used for the linear mapping. Note that memremap will only call this hook for regions that are not already mapped permanently.

Since this change results in memremap() to use attributes different from the ones used by ioremap_cache(), revert the change to pxa2xx-flash that moved it to memremap.

Changes since v2:
- add patch to bring back ioremap_cached() on ARM
- switch pxa2xx-flash back to ioremap_cached() not ioremap_cache()
- use arch_ioremap_caller not __arm_ioremap_caller() in patch #4
- deal with __iomem annotation of arch_ioremap_caller (patch #4)

Changes since v1/rfc:
- new patch #1 that reverts the ioremap_cache->memremap conversion for the pxa2xx-flash driver
- added Dan's ack to patch #2

Ard Biesheuvel (4):
ARM: reintroduce ioremap_cached() for creating cached I/O mappings
mtd: pxa2xx-flash: switch back from memremap to ioremap_cached
memremap: add arch specific hook for MEMREMAP_WB mappings
ARM: memremap: implement arch_memremap_wb()

Quoted 6 lines

 arch/arm/include/asm/io.h       | 12 ++++++++++++
 arch/arm/mm/ioremap.c           | 16 ++++++++++++++--
 drivers/mtd/maps/pxa2xx-flash.c |  6 +++---
 kernel/memremap.c               | 11 ++++++++---
 4 files changed, 37 insertions(+), 8 deletions(-)

For the series:

Quoted 1 line

Acked-by Dan Williams <[email protected]>

Thanks Dan,

With the added patch #1, I think it now makes the most sense for Russell to take the whole series via the ARM tree.

@Brian, David: any objections?