On Tue, May 21, 2019 at 10:44 AM Kirill Tkhai [off-list ref] wrote:

On 21.05.2019 19:43, Andy Lutomirski wrote:

quoted

On Tue, May 21, 2019 at 8:52 AM Kirill Tkhai [off-list ref] wrote:

quoted

On 21.05.2019 17:43, Andy Lutomirski wrote:

quoted

Do you mean that the code you sent rejects this case?  If so, please
document it.  In any case, I looked at the code, and it seems to be
trying to handle MAP_SHARED and MAP_ANONYMOUS.  I don't see where it
would reject copying a vDSO.

I prohibit all the VMAs, which contain on of flags: VM_HUGETLB|VM_DONTEXPAND|VM_PFNMAP|VM_IO.
I'll check carefully, whether it's enough for vDSO.

I think you could make the new syscall a lot more comprehensible bg
restricting it to just MAP_ANONYMOUS, by making it unmap the source,
or possibly both.  If the new syscall unmaps the source (in order so
that the source is gone before the newly mapped pages become
accessible), then you avoid issues in which you need to define
sensible semantics for what happens if both copies are accessed
simultaneously.


--Andy