Drivers: hv: vmbus: Leak pages if set_memory_encrypted() fails

A Linux kernel vulnerability in Hyper-V VMBus driver where encrypted memory operations can fail silently, allowing the untrusted host to trick the system into returning shared (unencrypted) memory back to the allocator. This can cause data leaks or system instability in confidential computing environments.

The VMBus driver fails to properly handle errors from set_memory_encrypted()/set_memory_decrypted() calls in CoCo VMs. When these calls fail, the pages remain in a shared/decrypted state but are freed back to the page allocator, violating memory isolation guarantees and creating a window for information disclosure or integrity violations via hostile host exploitation.