ioremap() calls pud_free_pmd_page() / pmd_free_pte_page() when it creates
a pud / pmd map.  The following preconditions are met at their entry.
 - All pte entries for a target pud/pmd address range have been cleared.
 - System-wide TLB purges have been peformed for a target pud/pmd address
   range.

The preconditions assure that there is no stale TLB entry for the range.
Speculation may not cache TLB entries since it requires all levels of page
entries, including ptes, to have P & A-bits set for an associated address.
However, speculation may cache pud/pmd entries (paging-structure caches)
when they have P-bit set.

Add a system-wide TLB purge (INVLPG) to a single page after clearing
pud/pmd entry's P-bit.

SDM 4.10.4.1, Operation that Invalidate TLBs and Paging-Structure Caches,
states that:
  INVLPG invalidates all paging-structure caches associated with the
  current PCID regardless of the liner addresses to which they correspond.

Fixes: 28ee90fe ("x86/mm: implement free pmd/pte page interfaces")
Signed-off-by: Toshi Kani <toshi.kani@hpe.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: mhocko@suse.com
Cc: akpm@linux-foundation.org
Cc: hpa@zytor.com
Cc: cpandya@codeaurora.org
Cc: linux-mm@kvack.org
Cc: linux-arm-kernel@lists.infradead.org
Cc: Joerg Roedel <joro@8bytes.org>
Cc: stable@vger.kernel.org
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: <stable@vger.kernel.org>
Link: https://lkml.kernel.org/r/20180627141348.21777-4-toshi.kani@hpe.com