On 10/31/22 17:54, Nadav Amit wrote:
On Oct 31, 2022, at 3:34 PM, Mike Kravetz mike.kravetz@oracle.com wrote:
madvise(MADV_DONTNEED) ends up calling zap_page_range() to clear the page tables associated with the address range. For hugetlb vmas, zap_page_range will call __unmap_hugepage_range_final. However, __unmap_hugepage_range_final assumes the passed vma is about to be removed and deletes the vma_lock to prevent pmd sharing as the vma is on the way out. In the case of madvise(MADV_DONTNEED) the vma remains, but the missing vma_lock prevents pmd sharing and could potentially lead to issues with truncation/fault races.
[snip]
index 978c17df053e..517c8cc8ccb9 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -3464,4 +3464,7 @@ madvise_set_anon_name(struct mm_struct *mm, unsigned long start, */ #define ZAP_FLAG_DROP_MARKER ((__force zap_flags_t) BIT(0))
+/* Set in unmap_vmas() to indicate an unmap call. Only used by hugetlb */ +#define ZAP_FLAG_UNMAP ((__force zap_flags_t) BIT(1))
PeterZ wants to add ZAP_FLAG_FORCE_FLUSH that would be set on zap_pte_range(). Not sure you would want to combine them both together, but at least be aware of potential conflict.
https://lore.kernel.org/all/Y1f7YvKuwOl1XEwU@hirez.programming.kicks-ass.net...
Ok, noted
[snip]
+#ifdef CONFIG_ADVISE_SYSCALLS +/*
- Similar setup as in zap_page_range(). madvise(MADV_DONTNEED) can not call
- zap_page_range for hugetlb vmas as __unmap_hugepage_range_final will delete
- the associated vma_lock.
- */
+void clear_hugetlb_page_range(struct vm_area_struct *vma, unsigned long start,
unsigned long end)+{
- struct mmu_notifier_range range;
- struct mmu_gather tlb;
- mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, vma->vm_mm,
start, end);- adjust_range_if_pmd_sharing_possible(vma, &range.start, &range.end);
- tlb_gather_mmu(&tlb, vma->vm_mm);
- update_hiwater_rss(vma->vm_mm);
- mmu_notifier_invalidate_range_start(&range);
- __unmap_hugepage_range_locking(&tlb, vma, start, end, NULL, 0);
- mmu_notifier_invalidate_range_end(&range);
- tlb_finish_mmu(&tlb);
} +#endif
I hate ifdef’s. And the second definition of clear_hugetlb_page_range() is confusing since it does not have an ifdef at all. . How about moving the ifdef’s into the function like being done in io_madvise_prep()? I think it is less confusing.
Dang!!! I sent the wrong version of the patch. clear_hugetlb_page_range is not even used here. I used Peter's idea to eliminate the need for this separate routine. And, this was a development version.
Really sorry about that.
Andrew, if you can please drop the version of the patch.