x86/mm/pat: Fix L1TF stable backport for CPA

Patch for stable only to fix boot resets caused by the L1TF patches.

Stable trees reverted the following patch

Revert "x86/mm/pat: Ensure cpa->pfn only contains page frame numbers"

    This reverts commit 87e2bd89 which is
    commit edc3b912 upstream.

but the L1TF patch backported here

   x86/mm/pat: Make set_memory_np() L1TF safe

    commit 958f79b9 upstream

    set_memory_np() is used to mark kernel mappings not present, but it has
    it's own open coded mechanism which does not have the L1TF protection of
    inverting the address bits.

assumed that cpa->pfn contains a PFN. With the above patch reverted
it does not, which causes the PMD to be set to an incorrect address
shifted by 12 bits, which can cause early boot reset on some
systems, like an Apollo Lake embedded system.

Convert the address to a PFN before passing it to pmd_pfn()

Thanks to Bernhard for bisecting and testing.

Cc: stable@vger.kernel.org # 4.4 and 4.9
Reported-by: Bernhard Kaindl <bernhard.kaindl@thalesgroup.com>
Tested-by: Bernhard Kaindl <bernhard.kaindl@thalesgroup.com>
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

arch/x86/mm/pageattr.c

@@ -1006,7 +1006,7 @@ static int populate_pmd(struct cpa_data *cpa,
 
 		pmd = pmd_offset(pud, start);
 
-		set_pmd(pmd, pmd_mkhuge(pfn_pmd(cpa->pfn,
+		set_pmd(pmd, pmd_mkhuge(pfn_pmd(cpa->pfn >> PAGE_SHIFT,
 					canon_pgprot(pmd_pgprot))));
 
 		start	  += PMD_SIZE;