arm64: kaslr: Adjust the offset to avoid Image across alignment boundary

arm64: kaslr: Adjust the offset to avoid Image across alignment boundary

With 16KB pages and a kernel Image larger than 16MB, the current
kaslr_early_init() logic for avoiding mappings across swapper table
boundaries fails since increasing the offset by kimg_sz just moves the
problem to the next boundary.

This patch rounds the offset down to (1 << SWAPPER_TABLE_SHIFT) if the
Image crosses a PMD_SIZE boundary.

Fixes: afd0e5a87670 ("arm64: kaslr: Fix up the kernel image alignment")
Cc: Ard Biesheuvel <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: Neeraj Upadhyay <[email protected]>
Signed-off-by: Catalin Marinas <[email protected]>
Signed-off-by: Will Deacon <[email protected]>