Hi Florian,
copy_vma will make a copy of the existing VMA leaving the old VMA
unchanged, so the source keeps its existing protections, this is what
makes it very useful along with userfaultfd.

Thanks,
Brian


On Mon, Jan 27, 2020 at 2:13 AM Florian Weimer [off-list ref] wrote:

* Brian Geffon:

quoted

When remapping an anonymous, private mapping, if MREMAP_DONTUNMAP is
set, the source mapping will not be removed. Instead it will be
cleared as if a brand new anonymous, private mapping had been created
atomically as part of the mremap() call.  If a userfaultfd was watching
the source, it will continue to watch the new mapping.  For a mapping
that is shared or not anonymous, MREMAP_DONTUNMAP will cause the
mremap() call to fail. MREMAP_DONTUNMAP implies that MREMAP_FIXED is
also used. The final result is two equally sized VMAs where the
destination contains the PTEs of the source.

What will be the protection flags of the source mapping?  Will they
remain unchanged?  Or PROT_NONE?

Thanks,
Florian