[PATCH v3 0/4] fix memremap on ARM

[Ard Biesheuvel]

On 4 March 2016 at 19:34, Dan Williams <dan.j.williams at intel.com> wrote:
> 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>

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?

Thanks,
Ard.