* Toshi Kani [off-list ref] wrote:

On architectures with CONFIG_HAVE_ARCH_HUGE_VMAP set, ioremap()
may create pud/pmd mappings.  Kernel panic was observed on arm64
systems with Cortex-A75 in the following steps as described by
Hanjun Guo.

1. ioremap a 4K size, valid page table will build,
2. iounmap it, pte0 will set to 0;
3. ioremap the same address with 2M size, pgd/pmd is unchanged,
   then set the a new value for pmd;
4. pte0 is leaked;
5. CPU may meet exception because the old pmd is still in TLB,
   which will lead to kernel panic.

This panic is not reproducible on x86.  INVLPG, called from iounmap,
purges all levels of entries associated with purged address on x86.

Where does x86 iounmap() do that?

x86 still has memory leak.
Add two interfaces, pud_free_pmd_page() and pmd_free_pte_page(),
which clear a given pud/pmd entry and free up a page for the lower
level entries.

This patch implements their stub functions on x86 and arm64, which
work as workaround.

At minimum the ordering of the patches is very confusing: why don't you introduce 
the new methods in patch #1, and then use them in patch #2?

Also please double check the coding style of your patches, there's a number of 
obvious problems of outright bad patterns and also cases where you clearly don't 
try to follow the (correct) style of existing code.

Thanks,

	Ingo