On Mon, Jul 12, 2021 at 09:05:45AM +0800, Longpeng (Mike, Cloud Infrastructure Service Product Dept.) wrote:

Let me describe my use case more clearly (just ignore if you're not interested
in it):

1. Prog A mmap() 4GB memory (anon or file-mapping), suppose the allocated VA
range is [0x40000000,0x140000000)

2. Prog A specifies [0x48000000,0x50000000) and [0x80000000,0x100000000) will be
shared by its child.

3. Prog A fork() Prog B and then Prog B exec() a new ELF binary.

4. Prog B notice the shared ranges (e.g. by input parameters or ...) and remap
them to a continuous VA range.

This is dangerous.  There must be an active step for Prog B to accept
Prog A's ranges into its address space.  Otherwise Prog A could almost
completely fill Prog B's address space and so control where Prog B
places its mappings.  It could also provoke a latent bug in Prog B
if it doesn't handle address space exhaustion gracefully.

I had a proposal to handle this.  Would it meet your requirements?
https://lore.kernel.org/lkml/20200730152250.GG23808@casper.infradead.org/ (local)