Patch series "Cleanup and fixups for vmemmap handling", v6.

This series contains cleanups to remove dead code that handles unaligned
cases for 4K and 1GB pages (patch#1 and patch#2) when removing the vemmmap
range, and a fix (patch#3) to handle the case when two vmemmap ranges
intersect the same PMD.

This patch (of 4):

remove_pte_table() is prepared to handle the case where either the start
or the end of the range is not PAGE aligned.  This cannot actually happen:

__populate_section_memmap enforces the range to be PMD aligned, so as long
as the size of the struct page remains multiple of 8, the vmemmap range
will be aligned to PAGE_SIZE.

Drop the dead code and place a VM_BUG_ON in vmemmap_{populate,free} to
catch nasty cases.  Note that the VM_BUG_ON is placed in there because
vmemmap_{populate,free= } is the gate of all removing and freeing page
tables logic.

Link: https://lkml.kernel.org/r/20210309214050.4674-1-osalvador@suse.de
Link: https://lkml.kernel.org/r/20210309214050.4674-2-osalvador@suse.deSigned-off-by: Oscar Salvador <osalvador@suse.de>
Suggested-by: David Hildenbrand <david@redhat.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: "H . Peter Anvin" <hpa@zytor.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>