nvme_driver: add timeout to controller ready/reset wait loops

[Novikov Kirill (knQzx)]

the enable() wait-for-RDY loop and Bar0::reset() wait-for-RDY-clear loop both poll with Backoff forever, so a stuck emulated device, a broken physical device, or a malicious VF that never lets the controller reach the expected state hangs the driver thread, and it also blocks the fuzzer from exercising setup-time parameters

this is the minimal fix from the issue's suggested fix: derive a deadline from CAP.TO (500ms units, 3s floor when TO is 0) and bound both loops

• ready loop bails with anyhow on expiry, matching the surrounding bail messages
• reset loop returns Err(csts) on expiry, signature unchanged since callers only log it
• unit test mocks a short CAP.TO and a stuck CSTS and checks NvmeDriver::new errors instead of hanging

kept out of scope on purpose: no full reset support or DMA quiescence, and nothing frees or unaliases DMA memory on the timeout path, that broader work is a bigger change and can follow up separately

fixes #3022

[Copilot]

Pull request overview

This PR hardens the NVMe driver’s controller bring-up/reset paths by adding a CAP.TO-derived deadline to previously-unbounded CSTS.RDY polling loops, preventing permanent hangs when a controller never reaches the expected ready state (including fuzzing scenarios).

Changes:

• Add a ready_timeout(cap) helper derived from CAP.TO (500ms units, 3s floor when TO=0) and use it to bound the CC.EN=1 “wait for RDY set” loop.
• Bound Bar0::reset()’s “wait for RDY clear” loop using the same CAP.TO-derived deadline (preserving the existing Result<(), u32> signature).
• Add a unit test that mocks CAP.TO and a stuck CSTS to assert NvmeDriver::new() errors instead of hanging, and implement set_mock_response_u32 to support that mock.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
vm/devices/storage/disk_nvme/nvme_driver/src/tests.rs	Adds a regression test for controller-ready timeout and enables mocking u32 MMIO reads (CSTS).
vm/devices/storage/disk_nvme/nvme_driver/src/registers.rs	Introduces CAP.TO-based timeout helper and applies it to the reset RDY-clear polling loop.
vm/devices/storage/disk_nvme/nvme_driver/src/driver.rs	Applies CAP.TO-based timeout to the controller-enable RDY-set polling loop and bails with an error on expiry.

[Novikov Kirill (knQzx)]

@microsoft-github-policy-service agree