Huge pmd sharing for hugetlbfs is racy with userfaultfd-wp because
userfaultfd-wp is always based on pgtable entries, so they cannot be shared.
Walk the hugetlb range and unshare all such mappings if there is, right before
UFFDIO_REGISTER will succeed and return to userspace.
This will pair with want_pmd_share() in hugetlb code so that huge pmd sharing
is completely disabled for userfaultfd-wp registered range.
Signed-off-by: Peter Xu <pet...@redhat.com>
---
fs/userfaultfd.c | 43 ++++++++++++++++++++++++++++++++++++
include/linux/mmu_notifier.h | 1 +
2 files changed, 44 insertions(+)
diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 3537a43b69c9..3190dff39d6c 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -15,6 +15,7 @@
#include <linux/sched/signal.h>
#include <linux/sched/mm.h>
#include <linux/mm.h>
+#include <linux/mmu_notifier.h>
#include <linux/poll.h>
#include <linux/slab.h>
#include <linux/seq_file.h>
@@ -1198,6 +1199,45 @@ static ssize_t userfaultfd_read(struct file *file, char
__user *buf,
}
}
+/*
+ * This function will unconditionally remove all the shared pmd pgtable entries
+ * within the specific vma for a hugetlbfs memory range.
+ */
+static void hugetlb_unshare_all_pmds(struct vm_area_struct *vma)
+{
+ struct hstate *h = hstate_vma(vma);
+ unsigned long sz = huge_page_size(h);
+ struct mm_struct *mm = vma->vm_mm;
+ struct mmu_notifier_range range;
+ unsigned long address;
+ spinlock_t *ptl;
+ pte_t *ptep;
+
+ /*
+ * No need to call adjust_range_if_pmd_sharing_possible(), because
+ * we're going to operate on the whole vma
+ */
+ mmu_notifier_range_init(&range, MMU_NOTIFY_HUGETLB_UNSHARE,
+ 0, vma, mm, vma->vm_start, vma->vm_end);
+ mmu_notifier_invalidate_range_start(&range);
+ i_mmap_lock_write(vma->vm_file->f_mapping);
+ for (address = vma->vm_start; address < vma->vm_end; address += sz) {
+ ptep = huge_pte_offset(mm, address, sz);
+ if (!ptep)
+ continue;
+ ptl = huge_pte_lock(h, mm, ptep);
+ huge_pmd_unshare(mm, vma, &address, ptep);
+ spin_unlock(ptl);
+ }
+ flush_hugetlb_tlb_range(vma, vma->vm_start, vma->vm_end);
+ i_mmap_unlock_write(vma->vm_file->f_mapping);
+ /*
+ * No need to call mmu_notifier_invalidate_range(), see
+ * Documentation/vm/mmu_notifier.rst.
+ */
+ mmu_notifier_invalidate_range_end(&range);
+}
+
static void __wake_userfault(struct userfaultfd_ctx *ctx,
struct userfaultfd_wake_range *range)
{
@@ -1456,6 +1496,9 @@ static int userfaultfd_register(struct userfaultfd_ctx
*ctx,
vma->vm_flags = new_flags;
vma->vm_userfaultfd_ctx.ctx = ctx;
+ if (is_vm_hugetlb_page(vma) && uffd_disable_huge_pmd_share(vma))
+ hugetlb_unshare_all_pmds(vma);
+
skip:
prev = vma;
start = vma->vm_end;
diff --git a/include/linux/mmu_notifier.h b/include/linux/mmu_notifier.h
index b8200782dede..ff50c8528113 100644
--- a/include/linux/mmu_notifier.h
+++ b/include/linux/mmu_notifier.h
@@ -51,6 +51,7 @@ enum mmu_notifier_event {
MMU_NOTIFY_SOFT_DIRTY,
MMU_NOTIFY_RELEASE,
MMU_NOTIFY_MIGRATE,
+ MMU_NOTIFY_HUGETLB_UNSHARE,
};
#define MMU_NOTIFIER_RANGE_BLOCKABLE (1 << 0)
--
2.26.2
