Re: [PATCH] khugepaged: collapse_pte_mapped_thp() flush the right range

From: Kirill A. Shutemov
Date: Sun Aug 02 2020 - 17:07:36 EST

On Sun, Aug 02, 2020 at 12:12:42PM -0700, Hugh Dickins wrote:
> pmdp_collapse_flush() should be given the start address at which the huge
> page is mapped, haddr: it was given addr, which at that point has been
> used as a local variable, incremented to the end address of the extent.
> Found by source inspection while chasing a hugepage locking bug, which
> I then could not explain by this. At first I thought this was very bad;
> then saw that all of the page translations that were not flushed would
> actually still point to the right pages afterwards, so harmless; then
> realized that I know nothing of how different architectures and models
> cache intermediate paging structures, so maybe it matters after all -
> particularly since the page table concerned is immediately freed.
> Much easier to fix than to think about.
> Fixes: 27e1f8273113 ("khugepaged: enable collapse pmd for pte-mapped THP")
> Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx # v5.4+

Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>

Kirill A. Shutemov