Hi Dan,

Recently, Redhat reported that nvml test suite failed on QEMU/KVM,
more detailed info please refer to:
    https://bugzilla.redhat.com/show_bug.cgi?id=1365721

The reason for this bug is that the memory region created by mmap()
on the dax-based file was gone so that the region can not be found
in /proc/self/smaps during the runtime.

This is a simple way to trigger this issue:
    mount -o dax /dev/pmem0 /mnt/pmem/
    vim /mnt/pmem/xxx
then 'vim' is crashed due to segment fault.

This bug can be reproduced on your tree, the top commit is
10d7902fa0e82b (dax: unmap/truncate on device shutdown), the kernel
configure file is attached.

Your thought or comment is highly appreciated.

Thanks!