* [PATCH v2] mm/khugepaged: check compound_order() in collapse_pte_mapped_thp()
@ 2022-09-22 22:27 Zach O'Keefe
2022-09-26 18:13 ` Yang Shi
0 siblings, 1 reply; 3+ messages in thread
From: Zach O'Keefe @ 2022-09-22 22:27 UTC (permalink / raw)
To: Andrew Morton; +Cc: linux-mm, Yang Shi, Zach O'Keefe
By the time we lock a page in collapse_pte_mapped_thp(), the page
mapped by the address pushed onto the slot's .pte_mapped_thp[] array
might have changed arbitrarily since we last looked at it. We
revalidate that the page is still the head of a compound page, but we
don't revalidate if the compound page is of order HPAGE_PMD_ORDER before
applying rmap and page table updates.
Since the kernel now supports large folios of arbitrary order, and since
replacing page's pte mappings by a pmd mapping only makes sense for
compound pages of order HPAGE_PMD_ORDER, revalidate that the compound
order is indeed of order HPAGE_PMD_ORDER before proceeding.
Link: https://lore.kernel.org/linux-mm/CAHbLzkon+2ky8v9ywGcsTUgXM_B35jt5NThYqQKXW2YV_GUacw@mail.gmail.com/
Suggested-by: Yang Shi <shy828301@gmail.com>
Signed-off-by: Zach O'Keefe <zokeefe@google.com>
---
mm/khugepaged.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 57af2c841b41..40fd9f7b3ed3 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1399,6 +1399,9 @@ void collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr)
if (!PageHead(hpage))
goto drop_hpage;
+ if (compound_order(hpage) != HPAGE_PMD_ORDER)
+ goto drop_hpage;
+
if (find_pmd_or_thp_or_none(mm, haddr, &pmd) != SCAN_SUCCEED)
goto drop_hpage;
--
2.37.3.998.g577e59143f-goog
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH v2] mm/khugepaged: check compound_order() in collapse_pte_mapped_thp()
2022-09-22 22:27 [PATCH v2] mm/khugepaged: check compound_order() in collapse_pte_mapped_thp() Zach O'Keefe
@ 2022-09-26 18:13 ` Yang Shi
2022-09-26 18:15 ` Zach O'Keefe
0 siblings, 1 reply; 3+ messages in thread
From: Yang Shi @ 2022-09-26 18:13 UTC (permalink / raw)
To: Zach O'Keefe; +Cc: Andrew Morton, linux-mm
On Thu, Sep 22, 2022 at 3:27 PM Zach O'Keefe <zokeefe@google.com> wrote:
>
> By the time we lock a page in collapse_pte_mapped_thp(), the page
> mapped by the address pushed onto the slot's .pte_mapped_thp[] array
> might have changed arbitrarily since we last looked at it. We
> revalidate that the page is still the head of a compound page, but we
> don't revalidate if the compound page is of order HPAGE_PMD_ORDER before
> applying rmap and page table updates.
>
> Since the kernel now supports large folios of arbitrary order, and since
> replacing page's pte mappings by a pmd mapping only makes sense for
> compound pages of order HPAGE_PMD_ORDER, revalidate that the compound
> order is indeed of order HPAGE_PMD_ORDER before proceeding.
>
> Link: https://lore.kernel.org/linux-mm/CAHbLzkon+2ky8v9ywGcsTUgXM_B35jt5NThYqQKXW2YV_GUacw@mail.gmail.com/
> Suggested-by: Yang Shi <shy828301@gmail.com>
> Signed-off-by: Zach O'Keefe <zokeefe@google.com>
Reviewed-by: Yang Shi <shy828301@gmail.com>
> ---
> mm/khugepaged.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index 57af2c841b41..40fd9f7b3ed3 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -1399,6 +1399,9 @@ void collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr)
> if (!PageHead(hpage))
> goto drop_hpage;
>
> + if (compound_order(hpage) != HPAGE_PMD_ORDER)
> + goto drop_hpage;
> +
> if (find_pmd_or_thp_or_none(mm, haddr, &pmd) != SCAN_SUCCEED)
> goto drop_hpage;
>
> --
> 2.37.3.998.g577e59143f-goog
>
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2022-09-26 18:15 UTC | newest]
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2022-09-22 22:27 [PATCH v2] mm/khugepaged: check compound_order() in collapse_pte_mapped_thp() Zach O'Keefe
2022-09-26 18:13 ` Yang Shi
2022-09-26 18:15 ` Zach O'Keefe
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