[Qemu-devel] [PATCH 06/23] userfaultfd: add VM_UFFD_MISSING and VM_UFFD_WP

[Andrea Arcangeli]

These two flags gets set in vma->vm_flags to tell the VM common code
if the userfaultfd is armed and in which mode (only tracking missing
faults, only tracking wrprotect faults or both). If neither flags is
set it means the userfaultfd is not armed on the vma.

Signed-off-by: Andrea Arcangeli <address@hidden>
---
 fs/proc/task_mmu.c | 2 ++
 include/linux/mm.h | 2 ++
 kernel/fork.c      | 2 +-
 3 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 6dee68d..58be92e 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -597,6 +597,8 @@ static void show_smap_vma_flags(struct seq_file *m, struct 
vm_area_struct *vma)
                [ilog2(VM_HUGEPAGE)]    = "hg",
                [ilog2(VM_NOHUGEPAGE)]  = "nh",
                [ilog2(VM_MERGEABLE)]   = "mg",
+               [ilog2(VM_UFFD_MISSING)]= "um",
+               [ilog2(VM_UFFD_WP)]     = "uw",
        };
        size_t i;
 
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 2923a51..7fccd22 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -123,8 +123,10 @@ extern unsigned int kobjsize(const void *objp);
 #define VM_MAYSHARE    0x00000080
 
 #define VM_GROWSDOWN   0x00000100      /* general info on the segment */
+#define VM_UFFD_MISSING        0x00000200      /* missing pages tracking */
 #define VM_PFNMAP      0x00000400      /* Page-ranges managed without "struct 
page", just pure PFN */
 #define VM_DENYWRITE   0x00000800      /* ETXTBSY on write attempts.. */
+#define VM_UFFD_WP     0x00001000      /* wrprotect pages tracking */
 
 #define VM_LOCKED      0x00002000
 #define VM_IO           0x00004000     /* Memory mapped I/O or similar */
diff --git a/kernel/fork.c b/kernel/fork.c
index 430141b..56d1ddf 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -449,7 +449,7 @@ static int dup_mmap(struct mm_struct *mm, struct mm_struct 
*oldmm)
                tmp->vm_mm = mm;
                if (anon_vma_fork(tmp, mpnt))
                        goto fail_nomem_anon_vma_fork;
-               tmp->vm_flags &= ~VM_LOCKED;
+               tmp->vm_flags &= ~(VM_LOCKED|VM_UFFD_MISSING|VM_UFFD_WP);
                tmp->vm_next = tmp->vm_prev = NULL;
                tmp->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
                file = tmp->vm_file;