On Thu, Aug 20, 2020 at 01:04:24PM -0700, Mike Kravetz wrote:
> On 8/19/20 5:21 AM, gregkh@xxxxxxxxxxxxxxxxxxx wrote:
> >
> > The patch below does not apply to the 4.4-stable tree.
> > If someone wants it applied there, or to any other stable or longterm
> > tree, then please email the backport, including the original git commit
> > id to <stable@xxxxxxxxxxxxxxx>.
> >
> > thanks,
> >
> > greg k-h
>
> >From d43b8a81c7f921aa52d55817390384053cd7be21 Mon Sep 17 00:00:00 2001
> From: Peter Xu <peterx@xxxxxxxxxx>
> Date: Thu, 20 Aug 2020 10:38:02 -0700
> Subject: [PATCH] mm/hugetlb: fix calculation of
> adjust_range_if_pmd_sharing_possible
>
> commit 75802ca66354a39ab8e35822747cd08b3384a99a upstream
>
> This is found by code observation only.
>
> Firstly, the worst case scenario should assume the whole range was covered
> by pmd sharing. The old algorithm might not work as expected for ranges
> like (1g-2m, 1g+2m), where the adjusted range should be (0, 1g+2m) but the
> expected range should be (0, 2g).
>
> Since at it, remove the loop since it should not be required. With that,
> the new code should be faster too when the invalidating range is huge.
>
> Mike said:
>
> : With range (1g-2m, 1g+2m) within a vma (0, 2g) the existing code will only
> : adjust to (0, 1g+2m) which is incorrect.
> :
> : We should cc stable. The original reason for adjusting the range was to
> : prevent data corruption (getting wrong page). Since the range is not
> : always adjusted correctly, the potential for corruption still exists.
> :
> : However, I am fairly confident that adjust_range_if_pmd_sharing_possible
> : is only gong to be called in two cases:
> :
> : 1) for a single page
> : 2) for range == entire vma
> :
> : In those cases, the current code should produce the correct results.
> :
> : To be safe, let's just cc stable.
>
> Fixes: 017b1660df89 ("mm: migration: fix migration of huge PMD shared pages")
> Signed-off-by: Peter Xu <peterx@xxxxxxxxxx>
> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Reviewed-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx>
> Link: http://lkml.kernel.org/r/20200730201636.74778-1-peterx@xxxxxxxxxx
> Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
> ---
> mm/hugetlb.c | 25 +++++++++++--------------
Thanks for all of the backports, now queued up.
greg k-h
