On Wed, 16 Nov 2016, Dan Williams wrote: > The device-dax implementation originally tried to be tricky and allow > private read-only mappings, but in the process allowed writable > MAP_PRIVATE + MAP_NORESERVE mappings. For simplicity and predictability > just fail all private mapping attempts since device-dax memory is > statically allocated and will never support overcommit. > > Cc: <stable(a)vger.kernel.org&gt; > Cc: Dave Hansen <dave.hansen(a)linux.intel.com&gt; > Fixes: dee410792419 ("/dev/dax, core: file operations and dax-mmap") > Reported-by: Pawel Lebioda <pawel.lebioda(a)intel.com&gt; > Signed-off-by: Dan Williams <dan.j.williams(a)intel.com&gt; > --- > drivers/dax/dax.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/drivers/dax/dax.c b/drivers/dax/dax.c > index 0e499bfca41c..3d94ff20fdca 100644 > --- a/drivers/dax/dax.c > +++ b/drivers/dax/dax.c > @@ -270,8 +270,8 @@ static int check_vma(struct dax_dev *dax_dev, struct vm_area_struct *vma, > if (!dax_dev->alive) > return -ENXIO; > > - /* prevent private / writable mappings from being established */ > - if ((vma->vm_flags & (VM_NORESERVE|VM_SHARED|VM_WRITE)) == VM_WRITE) { > + /* prevent private mappings from being established */ > + if ((vma->vm_flags & VM_SHARED) != VM_SHARED) { I think that is more restrictive than you intended: haven't tried, but I believe it rejects a PROT_READ, MAP_SHARED, O_RDONLY fd mmap, leaving no way to mmap /dev/dax without write permission to it. See line 1393 of mm/mmap.c: the test you want is probably if (!(vma->vm_flags & VM_MAYSHARE))