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Restoring a snapshot and making one guest function call took about 12 VM exits; on a nested hypervisor each costs several microseconds. Each entry now costs one, the halt that ends it: - An entry returns its Yield as the guest function's result (a Vec<u8>: next wakeup, flags, status, then the call's result) rather than send it with a host call. The first entry after a restore reports a ready driver and a call in flight on that Yield, not with DriverReady and CallStarted host calls. - The resume entry carries the mounts, the clock, the resolver and, when it fits a host call's payload, the environment, which the kernel fetched with GetResumeState and, on the first call, GetEnvVars. - The kernel leaves the SYSCALL MSRs to hyperlight, which restores the ones the host declares. A kernel from before this (given with from_kernel) still works: its entries return nothing, it sends its Yield by host call, and GetResumeState stays for it. A result too short to be a Yield is an error of its own, MalformedYield. Bump the kernel to plat-hyperlight-v2 bd441efa -> fd70ccb9 (the three changes above, and bounds on the FlatBuffer offsets the guest reads), rebuild both kernels and the native test fixture, and bump SNAPSHOT_CONTRACT: every guest function now returns a Vec<u8>. Signed-off-by: danbugs <danilochiarlone@gmail.com>
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🟡 Changes recommended
The embedded kernels lack the new ABI, while legacy resume entries are called with an incompatible argument.
2 open findings
What changed in this PR
Optimizes restore and guest-call VM exits while testing a resident-scratch Hyperlight fork.
Changes:
- Returns
Yielddata through entry results and carries resume state directly. - Adds restore/environment tests and updates protocol documentation.
- Pins experimental Hyperlight dependencies and bumps snapshot compatibility.
| File | Description |
|---|---|
src/lib.rs |
Implements the new entry and resume protocol. |
tests/python.rs |
Tests environment restoration paths. |
docs/profiling.md |
Updates profiling examples. |
docs/fs.md |
Documents restored mount handling. |
docs/execution.md |
Documents entry results and resume state. |
docs/driver.md |
Updates driver restore behavior. |
docs/clock.md |
Updates restored clock behavior. |
CHANGELOG.md |
Records the protocol optimization. |
Cargo.toml |
Patches Hyperlight to an experimental fork. |
Cargo.lock |
Locks the fork revision. |
build.rs |
Bumps the snapshot contract. |
🧠 Review effort: Balanced
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| fits.then(|| (self.config.env_version(), env.as_str())), | ||
| ); | ||
| drop((resolv, env)); | ||
| let yielded = self.config.enter(&mut self.sandbox, "resume", (state,))?; |
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| ### Changed | ||
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| - Restoring a snapshot and making one guest function call takes two VM exits on x86_64, the halts that end its two entries, where it took about 12 (arm64 adds one: its kernel reseeds its CSPRNG from the host). An entry returns its `Yield` as the guest function's result. The `resume` entry carries the mounts, clock and resolver, and the environment when it fits a host call (a larger one is fetched by the first call). The kernel leaves the SYSCALL MSRs to hyperlight, which restores them. A kernel built before this, given with `from_kernel`, still works, sending its `Yield` and fetching its state by host call. A kernel built from these sources needs this `hluk` or later. |
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Patch hyperlight-host and hyperlight-common to danbugs/hyperlight c854bb43 (0.17.0 plus the scratch reset of hyperlight-dev/hyperlight#1901), to measure it in CI. Signed-off-by: danbugs <danilochiarlone@gmail.com>
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