[PATCH v8 1/2] hugetlb: don't delete vma_lock in hugetlb MADV_DONTNEED processing

Mike Kravetz
2022-11-08T01:19:44Z

madvise(MADV_DONTNEED) ends up calling zap_page_range() to clear 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.

This issue was originally reported here [1] as a BUG triggered in
page_try_dup_anon_rmap. Prior to the introduction of the hugetlb
vma_lock, __unmap_hugepage_range_final cleared the VM_MAYSHARE flag to
prevent pmd sharing. Subsequent faults on this vma were confused as
VM_MAYSHARE indicates a sharable vma, but was not set so page_mapping was
not set in new pages added to the page table. This resulted in pages that
appeared anonymous in a VM_SHARED vma and triggered the BUG.

Address issue by:
- Add a new zap flag ZAP_FLAG_UNMAP to indicate an unmap call from
unmap_vmas(). This is used to indicate the 'final' unmapping of a vma.
When called via MADV_DONTNEED, this flag is not set and the vm_lock is
not deleted.
- mmu notification is removed from __unmap_hugepage_range to avoid
duplication, and notification is added to the other calling routine
(unmap_hugepage_range).
- notification range in zap_page_range_single is updated to take into
account the possibility of hugetlb pmd sharing.
- zap_page_range_single renamed to __zap_page_range_single to be used
internally within mm/memory.c
- zap_vma_range() interface created to zap a range within a single vma.
- madvise_dontneed_single_vma is updated to call zap_vma_range instead of
zap_page_range as it only operates on a range within a single vma

[1] https://lore.kernel.org/lkml/CAO4mrfdLMXsao9RF4fUE8-Wfde8xmjsKrTNMNC9wjUb6JudD0g@mail.gmail.com/
Fixes: 90e7e7f5ef3f ("mm: enable MADV_DONTNEED for hugetlb mappings")
Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
Reported-by: Wei Chen <harperchen1110@gmail.com>
Cc: <stable@vger.kernel.org>
---
include/linux/mm.h | 5 +++++
mm/hugetlb.c | 45 +++++++++++++++++++++++++++------------------
mm/madvise.c | 4 ++--
mm/memory.c | 17 +++++++++++++----
4 files changed, 47 insertions(+), 24 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 978c17df053e..d205bcd9cd2e 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1840,6 +1840,8 @@ void zap_vma_ptes(struct vm_area_struct *vma, unsigned long address,
unsigned long size);
void zap_page_range(struct vm_area_struct *vma, unsigned long address,
unsigned long size);
+void zap_vma_range(struct vm_area_struct *vma, unsigned long address,
+ unsigned long size);
void unmap_vmas(struct mmu_gather *tlb, struct maple_tree *mt,
struct vm_area_struct *start_vma, unsigned long start,
unsigned long end);
@@ -3464,4 +3466,7 @@ 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))
+
#endif /* _LINUX_MM_H */
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index ceb47c4e183a..7c8fbce4441e 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -5072,7 +5072,6 @@ static void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct
struct page *page;
struct hstate *h = hstate_vma(vma);
unsigned long sz = huge_page_size(h);
- struct mmu_notifier_range range;
unsigned long last_addr_mask;
bool force_flush = false;

@@ -5087,13 +5086,6 @@ static void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct
tlb_change_page_size(tlb, sz);
tlb_start_vma(tlb, vma);

- /*
- * If sharing possible, alert mmu notifiers of worst case.
- */
- mmu_notifier_range_init(&range, MMU_NOTIFY_UNMAP, 0, vma, mm, start,
- end);
- adjust_range_if_pmd_sharing_possible(vma, &range.start, &range.end);
- mmu_notifier_invalidate_range_start(&range);
last_addr_mask = hugetlb_mask_last_page(h);
address = start;
for (; address < end; address += sz) {
@@ -5178,7 +5170,6 @@ static void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct
if (ref_page)
break;
}
- mmu_notifier_invalidate_range_end(&range);
tlb_end_vma(tlb, vma);

/*
@@ -5203,32 +5194,50 @@ void __unmap_hugepage_range_final(struct mmu_gather *tlb,
unsigned long end, struct page *ref_page,
zap_flags_t zap_flags)
{
+ bool final = zap_flags & ZAP_FLAG_UNMAP;
+
hugetlb_vma_lock_write(vma);
i_mmap_lock_write(vma->vm_file->f_mapping);

__unmap_hugepage_range(tlb, vma, start, end, ref_page, zap_flags);

/*
- * Unlock and free the vma lock before releasing i_mmap_rwsem. When
- * the vma_lock is freed, this makes the vma ineligible for pmd
- * sharing. And, i_mmap_rwsem is required to set up pmd sharing.
- * This is important as page tables for this unmapped range will
- * be asynchrously deleted. If the page tables are shared, there
- * will be issues when accessed by someone else.
+ * When called via zap_vma_range (MADV_DONTNEED), this is not the
+ * final unmap of the vma, and we do not want to delete the vma_lock.
*/
- __hugetlb_vma_unlock_write_free(vma);
-
- i_mmap_unlock_write(vma->vm_file->f_mapping);
+ if (final) {
+ /*
+ * Unlock and free the vma lock before releasing i_mmap_rwsem.
+ * When the vma_lock is freed, this makes the vma ineligible
+ * for pmd sharing. And, i_mmap_rwsem is required to set up
+ * pmd sharing. This is important as page tables for this
+ * unmapped range will be asynchrously deleted. If the page
+ * tables are shared, there will be issues when accessed by
+ * someone else.
+ */
+ __hugetlb_vma_unlock_write_free(vma);
+ i_mmap_unlock_write(vma->vm_file->f_mapping);
+ } else {
+ i_mmap_unlock_write(vma->vm_file->f_mapping);
+ hugetlb_vma_unlock_write(vma);
+ }
}

void unmap_hugepage_range(struct vm_area_struct *vma, unsigned long start,
unsigned long end, struct page *ref_page,
zap_flags_t zap_flags)
{
+ struct mmu_notifier_range range;
struct mmu_gather tlb;

+ mmu_notifier_range_init(&range, MMU_NOTIFY_UNMAP, 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);
+
__unmap_hugepage_range(&tlb, vma, start, end, ref_page, zap_flags);
+
+ mmu_notifier_invalidate_range_end(&range);
tlb_finish_mmu(&tlb);
}

diff --git a/mm/madvise.c b/mm/madvise.c
index c7105ec6d08c..9d2625b8029a 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -772,7 +772,7 @@ static int madvise_free_single_vma(struct vm_area_struct *vma,
* Application no longer needs these pages. If the pages are dirty,
* it's OK to just throw them away. The app will be more careful about
* data it wants to keep. Be sure to free swap resources too. The
- * zap_page_range call sets things up for shrink_active_list to actually free
+ * zap_vma_range call sets things up for shrink_active_list to actually free
* these pages later if no one else has touched them in the meantime,
* although we could add these pages to a global reuse list for
* shrink_active_list to pick up before reclaiming other pages.
@@ -790,7 +790,7 @@ static int madvise_free_single_vma(struct vm_area_struct *vma,
static long madvise_dontneed_single_vma(struct vm_area_struct *vma,
unsigned long start, unsigned long end)
{
- zap_page_range(vma, start, end - start);
+ zap_vma_range(vma, start, end - start);
return 0;
}

diff --git a/mm/memory.c b/mm/memory.c
index 6090124b64f1..af3a4724b464 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1717,7 +1717,7 @@ void zap_page_range(struct vm_area_struct *vma, unsigned long start,
}

/**
- * zap_page_range_single - remove user pages in a given range
+ * __zap_page_range_single - remove user pages in a given range
* @vma: vm_area_struct holding the applicable pages
* @address: starting address of pages to zap
* @size: number of bytes to zap
@@ -1725,7 +1725,7 @@ void zap_page_range(struct vm_area_struct *vma, unsigned long start,
*
* The range must fit into one VMA.
*/
-static void zap_page_range_single(struct vm_area_struct *vma, unsigned long address,
+static void __zap_page_range_single(struct vm_area_struct *vma, unsigned long address,
unsigned long size, struct zap_details *details)
{
struct mmu_notifier_range range;
@@ -1734,6 +1734,9 @@ static void zap_page_range_single(struct vm_area_struct *vma, unsigned long addr
lru_add_drain();
mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, vma->vm_mm,
address, address + size);
+ if (is_vm_hugetlb_page(vma))
+ 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);
@@ -1742,6 +1745,12 @@ static void zap_page_range_single(struct vm_area_struct *vma, unsigned long addr
tlb_finish_mmu(&tlb);
}

+void zap_vma_range(struct vm_area_struct *vma, unsigned long address,
+ unsigned long size)
+{
+ __zap_page_range_single(vma, address, size, NULL);
+}
+
/**
* zap_vma_ptes - remove ptes mapping the vma
* @vma: vm_area_struct holding ptes to be zapped
@@ -1760,7 +1769,7 @@ void zap_vma_ptes(struct vm_area_struct *vma, unsigned long address,
!(vma->vm_flags & VM_PFNMAP))
return;

- zap_page_range_single(vma, address, size, NULL);
+ __zap_page_range_single(vma, address, size, NULL);
}
EXPORT_SYMBOL_GPL(zap_vma_ptes);

@@ -3453,7 +3462,7 @@ static void unmap_mapping_range_vma(struct vm_area_struct *vma,
unsigned long start_addr, unsigned long end_addr,
struct zap_details *details)
{
- zap_page_range_single(vma, start_addr, end_addr - start_addr, details);
+ __zap_page_range_single(vma, start_addr, end_addr - start_addr, details);
}

static inline void unmap_mapping_range_tree(struct rb_root_cached *root,
--
2.37.3