[PATCH v3 0/4] fix memremap on ARM

[Dan Williams]

On Fri, Mar 4, 2016 at 1:48 AM, Ard Biesheuvel
<ard.biesheuvel at linaro.org> wrote:
> 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()
>
>  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:

Acked-by: Dan Williams <dan.j.williams at intel.com>