arm64/mm: Sanity check PTE address before runtime P4D/PUD folding

The runtime P4D/PUD folding logic assumes that the respective pgd_t* and
p4d_t* arguments are pointers into actual page tables that are part of
the hierarchy being operated on.

This may not always be the case, and we have been bitten once by this
already [0], where the argument was actually a stack variable, and in
this case, the logic does not work at all.

So let's add a VM_BUG_ON() for each case, to ensure that the address of
the provided page table entry is consistent with the address being
translated.

[0] https://lore.kernel.org/all/20240725090345.28461-1-will@kernel.org/T/#u



Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20241105093919.1312049-2-ardb+git@google.com


Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>