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. 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. Ard Biesheuvel (2): memremap: add arch specific hook for MEMREMAP_WB mappings ARM: memremap: implement arch_memremap_wb() arch/arm/include/asm/io.h | 3 +++ arch/arm/mm/ioremap.c | 11 +++++++++-- kernel/memremap.c | 11 ++++++++--- 3 files changed, 20 insertions(+), 5 deletions(-) -- 2.5.0
