arm64: Enforce BBM for huge IO/VMAP mappings

arm64: Enforce BBM for huge IO/VMAP mappings

ioremap_page_range doesn't honour break-before-make and attempts to put
down huge mappings (using p*d_set_huge) over the top of pre-existing
table entries. This leads to us leaking page table memory and also gives
rise to TLB conflicts and spurious aborts, which have been seen in
practice on Cortex-A75.

Until this has been resolved, refuse to put block mappings when the
existing entry is found to be present.

Fixes: 324420bf91f60 ("arm64: add support for ioremap() block mappings")
Reported-by: Hanjun Guo <[email protected]>
Reported-by: Lei Li <[email protected]>
Acked-by: Ard Biesheuvel <[email protected]>
Signed-off-by: Will Deacon <[email protected]>
Signed-off-by: Catalin Marinas <[email protected]>