On 8/19/20 5:21 AM, gregkh@xxxxxxxxxxxxxxxxxxx wrote:
>
> The patch below does not apply to the 5.4-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 f9a5ec220383e9326d4018f9da0529b56a52126e 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 | 24 ++++++++++--------------
1 file changed, 10 insertions(+), 14 deletions(-)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 2af1831596f2..2a83b03c54a6 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -4846,25 +4846,21 @@ 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);
}
/*
--
2.25.4
