[PATCH 21/23] hugetlb/userfaultfd: Only drop uffd-wp special pte if required

Peter Xu
2021-03-23T00:51:52Z

Just like what we've done with shmem uffd-wp special ptes, we shouldn't drop
uffd-wp special swap pte for hugetlb too, only if we're going to unmap the
whole vma, or we're punching a hole with safe locks held.

For example, remove_inode_hugepages() is safe to drop uffd-wp ptes, because it
has taken hugetlb fault mutex so that no concurrent page fault would trigger.
While the call to hugetlb_vmdelete_list() in hugetlbfs_punch_hole() is not
safe. That's why the previous call will be with ZAP_FLAG_DROP_FILE_UFFD_WP,
while the latter one won't be able to.

Signed-off-by: Peter Xu <peterx@redhat.com>
---
fs/hugetlbfs/inode.c | 15 +++++++++------
include/linux/hugetlb.h | 13 ++++++++-----
mm/hugetlb.c | 27 +++++++++++++++++++++------
mm/memory.c | 5 ++++-
4 files changed, 42 insertions(+), 18 deletions(-)

diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index d81f52b87bd7..5fe19e801a2b 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -399,7 +399,8 @@ static void remove_huge_page(struct page *page)
}

static void
-hugetlb_vmdelete_list(struct rb_root_cached *root, pgoff_t start, pgoff_t end)
+hugetlb_vmdelete_list(struct rb_root_cached *root, pgoff_t start, pgoff_t end,
+ unsigned long zap_flags)
{
struct vm_area_struct *vma;

@@ -432,7 +433,7 @@ hugetlb_vmdelete_list(struct rb_root_cached *root, pgoff_t start, pgoff_t end)
}

unmap_hugepage_range(vma, vma->vm_start + v_offset, v_end,
- NULL);
+ NULL, zap_flags);
}
}

@@ -513,7 +514,8 @@ static void remove_inode_hugepages(struct inode *inode, loff_t lstart,
mutex_lock(&hugetlb_fault_mutex_table[hash]);
hugetlb_vmdelete_list(&mapping->i_mmap,
index * pages_per_huge_page(h),
- (index + 1) * pages_per_huge_page(h));
+ (index + 1) * pages_per_huge_page(h),
+ ZAP_FLAG_DROP_FILE_UFFD_WP);
i_mmap_unlock_write(mapping);
}

@@ -579,7 +581,8 @@ static void hugetlb_vmtruncate(struct inode *inode, loff_t offset)
i_mmap_lock_write(mapping);
i_size_write(inode, offset);
if (!RB_EMPTY_ROOT(&mapping->i_mmap.rb_root))
- hugetlb_vmdelete_list(&mapping->i_mmap, pgoff, 0);
+ hugetlb_vmdelete_list(&mapping->i_mmap, pgoff, 0,
+ ZAP_FLAG_DROP_FILE_UFFD_WP);
i_mmap_unlock_write(mapping);
remove_inode_hugepages(inode, offset, LLONG_MAX);
}
@@ -612,8 +615,8 @@ static long hugetlbfs_punch_hole(struct inode *inode, loff_t offset, loff_t len)
i_mmap_lock_write(mapping);
if (!RB_EMPTY_ROOT(&mapping->i_mmap.rb_root))
hugetlb_vmdelete_list(&mapping->i_mmap,
- hole_start >> PAGE_SHIFT,
- hole_end >> PAGE_SHIFT);
+ hole_start >> PAGE_SHIFT,
+ hole_end >> PAGE_SHIFT, 0);
i_mmap_unlock_write(mapping);
remove_inode_hugepages(inode, hole_start, hole_end);
inode_unlock(inode);
diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index 92710600596e..4047fa042782 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -121,14 +121,15 @@ long follow_hugetlb_page(struct mm_struct *, struct vm_area_struct *,
unsigned long *, unsigned long *, long, unsigned int,
int *);
void unmap_hugepage_range(struct vm_area_struct *,
- unsigned long, unsigned long, struct page *);
+ unsigned long, unsigned long, struct page *,
+ unsigned long);
void __unmap_hugepage_range_final(struct mmu_gather *tlb,
struct vm_area_struct *vma,
unsigned long start, unsigned long end,
- struct page *ref_page);
+ struct page *ref_page, unsigned long zap_flags);
void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct *vma,
unsigned long start, unsigned long end,
- struct page *ref_page);
+ struct page *ref_page, unsigned long zap_flags);
void hugetlb_report_meminfo(struct seq_file *);
int hugetlb_report_node_meminfo(char *buf, int len, int nid);
void hugetlb_show_meminfo(void);
@@ -361,14 +362,16 @@ static inline unsigned long hugetlb_change_protection(

static inline void __unmap_hugepage_range_final(struct mmu_gather *tlb,
struct vm_area_struct *vma, unsigned long start,
- unsigned long end, struct page *ref_page)
+ unsigned long end, struct page *ref_page,
+ unsigned long zap_flags)
{
BUG();
}

static inline void __unmap_hugepage_range(struct mmu_gather *tlb,
struct vm_area_struct *vma, unsigned long start,
- unsigned long end, struct page *ref_page)
+ unsigned long end, struct page *ref_page,
+ unsigned long zap_flags)
{
BUG();
}
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index d4acf9d9d087..deeae6d40dad 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -3936,7 +3936,7 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src,

void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct *vma,
unsigned long start, unsigned long end,
- struct page *ref_page)
+ struct page *ref_page, unsigned long zap_flags)
{
struct mm_struct *mm = vma->vm_mm;
unsigned long address;
@@ -3988,6 +3988,19 @@ void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct *vma,
continue;
}

+ if (unlikely(is_swap_special_pte(pte))) {
+ WARN_ON_ONCE(!pte_swp_uffd_wp_special(pte));
+ /*
+ * Only drop the special swap uffd-wp pte if
+ * e.g. unmapping a vma or punching a hole (with proper
+ * lock held so that concurrent page fault won't happen).
+ */
+ if (zap_flags & ZAP_FLAG_DROP_FILE_UFFD_WP)
+ huge_pte_clear(mm, address, ptep, sz);
+ spin_unlock(ptl);
+ continue;
+ }
+
/*
* Migrating hugepage or HWPoisoned hugepage is already
* unmapped and its refcount is dropped, so just clear pte here.
@@ -4039,9 +4052,10 @@ void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct *vma,

void __unmap_hugepage_range_final(struct mmu_gather *tlb,
struct vm_area_struct *vma, unsigned long start,
- unsigned long end, struct page *ref_page)
+ unsigned long end, struct page *ref_page,
+ unsigned long zap_flags)
{
- __unmap_hugepage_range(tlb, vma, start, end, ref_page);
+ __unmap_hugepage_range(tlb, vma, start, end, ref_page, zap_flags);

/*
* Clear this flag so that x86's huge_pmd_share page_table_shareable
@@ -4057,12 +4071,13 @@ void __unmap_hugepage_range_final(struct mmu_gather *tlb,
}

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

tlb_gather_mmu(&tlb, vma->vm_mm);
- __unmap_hugepage_range(&tlb, vma, start, end, ref_page);
+ __unmap_hugepage_range(&tlb, vma, start, end, ref_page, zap_flags);
tlb_finish_mmu(&tlb);
}

@@ -4117,7 +4132,7 @@ static void unmap_ref_private(struct mm_struct *mm, struct vm_area_struct *vma,
*/
if (!is_vma_resv_set(iter_vma, HPAGE_RESV_OWNER))
unmap_hugepage_range(iter_vma, address,
- address + huge_page_size(h), page);
+ address + huge_page_size(h), page, 0);
}
i_mmap_unlock_write(mapping);
}
diff --git a/mm/memory.c b/mm/memory.c
index 766946d3eab0..4bf7f8e83733 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1515,8 +1515,11 @@ static void unmap_single_vma(struct mmu_gather *tlb,
* safe to do nothing in this case.
*/
if (vma->vm_file) {
+ unsigned long zap_flags = details ?
+ details->zap_flags : 0;
i_mmap_lock_write(vma->vm_file->f_mapping);
- __unmap_hugepage_range_final(tlb, vma, start, end, NULL);
+ __unmap_hugepage_range_final(tlb, vma, start, end,
+ NULL, zap_flags);
i_mmap_unlock_write(vma->vm_file->f_mapping);
}
} else
--
2.26.2