On Thu, Aug 17, 2017 at 06:08:12PM +0200, Jan Kara wrote: > Pretty crude for now... > > Signed-off-by: Jan Kara <jack@xxxxxxx> One other thing that should probably be wired up before this is all said and done is the VmFlag string in /proc/<pid>/smaps. Right now when we set this flag it ends up as ??: 7f44e6cbd000-7f44e6dbd000 rw-s 00000000 103:00 12 /root/dax/data Size: 1024 kB Rss: 0 kB Pss: 0 kB Shared_Clean: 0 kB Shared_Dirty: 0 kB Private_Clean: 0 kB Private_Dirty: 0 kB Referenced: 0 kB Anonymous: 0 kB LazyFree: 0 kB AnonHugePages: 0 kB ShmemPmdMapped: 0 kB Shared_Hugetlb: 0 kB Private_Hugetlb: 0 kB Swap: 0 kB SwapPss: 0 kB KernelPageSize: 4 kB MMUPageSize: 4 kB Locked: 0 kB VmFlags: rd wr sh mr mw me ms ?? mm hg The quick one-liner at the end of this patch changes that to: 7fe30e87f000-7fe30e97f000 rw-s 00000000 103:00 12 /root/dax/data Size: 1024 kB Rss: 0 kB Pss: 0 kB Shared_Clean: 0 kB Shared_Dirty: 0 kB Private_Clean: 0 kB Private_Dirty: 0 kB Referenced: 0 kB Anonymous: 0 kB LazyFree: 0 kB AnonHugePages: 0 kB ShmemPmdMapped: 0 kB Shared_Hugetlb: 0 kB Private_Hugetlb: 0 kB Swap: 0 kB SwapPss: 0 kB KernelPageSize: 4 kB MMUPageSize: 4 kB Locked: 0 kB VmFlags: rd wr sh mr mw me ms sf mm hg I think that of software can rely on this flag for userspace flushing without worrying about any new TOCTOU races because there isn't a way to unset the VM_SYNC flag once it is set - it should be valid as long as the mmap() remains open and the mmap'd address is valid. --- 8< --- fs/proc/task_mmu.c | 1 + 1 file changed, 1 insertion(+) diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c index b836fd6..a2a82ed 100644 --- a/fs/proc/task_mmu.c +++ b/fs/proc/task_mmu.c @@ -650,6 +650,7 @@ static void show_smap_vma_flags(struct seq_file *m, struct vm_area_struct *vma) [ilog2(VM_ACCOUNT)] = "ac", [ilog2(VM_NORESERVE)] = "nr", [ilog2(VM_HUGETLB)] = "ht", + [ilog2(VM_SYNC)] = "sf", [ilog2(VM_ARCH_1)] = "ar", [ilog2(VM_DONTDUMP)] = "dd", #ifdef CONFIG_MEM_SOFT_DIRTY
