Self Review: UVM_ENABLE_READ_DUPLICATION

[anthonywu]

Fix for google#12034

self review only, will send upstream when tested

pending time to test this with this test plan:

1. rent a Nvidia online GPU, either bare metal or VM (TBD if VM is sufficient)
2. install Docker runtime on it
3. docker run --runtime=runsc ...
4. verify fix with the snippet posted in bug report

Test Env

1. Azure VM GPU size Standard_NC4as_T4_v3
2. OS: Ubuntu Server 24.04 with Azure
3. Installed Docker runtime: https://docs.docker.com/engine/install/ubuntu/
4. Installed bazel: https://bazel.build/install/ubuntu
5. Installed nvidia drivers: https://documentation.ubuntu.com/server/how-to/graphics/install-nvidia-drivers/
6. compiled runsc according to gvisor README build instructions
7. linked runsc to /usr/bin/local/runsc