[PATCH v5sub1 8/8] arm64: allow kernel Image to be loaded anywhere in physical memory

Ard Biesheuvel ard.biesheuvel at linaro.org
Mon Feb 1 07:13:52 PST 2016

On 1 February 2016 at 16:06, Catalin Marinas <catalin.marinas at arm.com> wrote:
> On Mon, Feb 01, 2016 at 11:54:53AM +0100, Ard Biesheuvel wrote:
>> Note that limiting memory using mem= is not unambiguous anymore after
>> this change, considering that the kernel may be at the top of physical
>> memory, and clipping from the bottom rather than the top will discard
>> any 32-bit DMA addressable memory first. To deal with this, the handling
>> of mem= is reimplemented to clip top down, but take special care not to
>> clip memory that covers the kernel image.
> I may have forgotten the reason - why do we need to avoid clipping the
> memory that covers the kernel image? It's already mapped in the vmalloc
> area, so we wouldn't need it in the linear map as well.

Good question. Originally, I needed it for swapper_pg_dir, whose
pud/pmd/pte levels were accessed via __va() translations of the values
found in the higher-up table entries, but after Mark's patches, only
the top level pgd of swapper_pg_dir is still used. Similarly, for
idmap_pg_dir, we don't change any mappings at runtime so the same
applies there I think.

I will try dropping this, and see what happens.


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