On 8/19/20 5:21 AM, gregkh@linuxfoundation.org wrote:

The patch below does not apply to the 4.9-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@vger.kernel.org.

thanks,

greg k-h

From fe0d63dd32343cab510846ada110079ec3ebafbb Mon Sep 17 00:00:00 2001

From: Peter Xu peterx@redhat.com 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@redhat.com Signed-off-by: Andrew Morton akpm@linux-foundation.org Reviewed-by: Mike Kravetz mike.kravetz@oracle.com Cc: Andrea Arcangeli aarcange@redhat.com Cc: Matthew Wilcox willy@infradead.org Cc: stable@vger.kernel.org Link: http://lkml.kernel.org/r/20200730201636.74778-1-peterx@redhat.com Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Mike Kravetz mike.kravetz@oracle.com --- mm/hugetlb.c | 24 ++++++++++-------------- 1 file changed, 10 insertions(+), 14 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 9914da93069e..2c22ea7a2013 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -4380,25 +4380,21 @@ static bool vma_shareable(struct vm_area_struct *vma, unsigned long addr) void adjust_range_if_pmd_sharing_possible(struct vm_area_struct *vma, unsigned long *start, unsigned long *end) { - unsigned long check_addr = *start; + unsigned long a_start, a_end;

if (!(vma->vm_flags & VM_MAYSHARE)) return;

- for (check_addr = *start; check_addr < *end; check_addr += PUD_SIZE) { - unsigned long a_start = check_addr & PUD_MASK; - unsigned long a_end = a_start + PUD_SIZE; + /* Extend the range to be PUD aligned for a worst case scenario */ + a_start = ALIGN_DOWN(*start, PUD_SIZE); + a_end = ALIGN(*end, PUD_SIZE);

- /* - * If sharing is possible, adjust start/end if necessary. - */ - if (range_in_vma(vma, a_start, a_end)) { - if (a_start < *start) - *start = a_start; - if (a_end > *end) - *end = a_end; - } - } + /* + * Intersect the range with the vma range, since pmd sharing won't be + * across vma after all + */ + *start = max(vma->vm_start, a_start); + *end = min(vma->vm_end, a_end); }

/*