[PATCH v3 04/11] arm64: use fixmap region for permanent FDT mapping

[Ard Biesheuvel]

On 13 apr. 2015, at 18:26, Mark Rutland <mark.rutland at arm.com> wrote:

>> I was wondering: this code now always maps the full 4 MB, also on 64k
>> pages, even if in the majority of cases, the actual FDT is much
>> smaller. Do you think there is a downside to that?
> 
> The two cases I can think of as problematic are when the FDT is in the
> last 2M of RAM, or in a 2M region immediately before some carveout which
> won't use MT_NORMAL attributes.
> 
> We could solve those by only mapping however many 2M chunks are
> necessary, or we could keep the requirement that it fits within a
> naturally-aligned 2M region for now.
> 

I strongly prefer the former, since otherwise, you always need to verify the allocation explicitly, for an fdt of any size, and it turns out the logic is easily updated to move the vetting into fixmap_remap_fdt() and check the magic and size after mapping the first chunk, and set pfn_end accordingly

> I don't see that this should yield significant problems otherwise.
> 
> Mark.