docs: Remove version restriction on IgvmNativeVpContextX64

[jethrogb]

The documentation mentions a file format version restriction for IgvmNativeVpContextX64. However, neither the generator nor the parser enforce this: they will happily generate/parse IGVM files with a IGVM_VHT_VP_CONTEXT header when the revision is 1 and the platform type is NATIVE. QEMU will happily launch such IGVMs correctly. As such, this entire restriction seems to be meaningless.

[chris-oo]

I disagree, this is a bug in the igvm crate as the parser should be enforcing this. Would you like to submit a fix for that instead?

[chris-oo]

If not, feel free to file an issue and I'll see if I can get to it next week. I suspect we aren't enforcing many v2 version requirements that we should be.

[jethrogb]

Changing the behavior now would break downstream.

[chris-oo]

I think we will need to change the behavior in the next version, because we cannot guarantee that this is stable which is the point of the unstable flag. Although, maybe we can relax it in this specific case, but let me think about that over the weekend.

[jethrogb]

The igvm crate doesn't have any features, and the igvm_c code also doesn't require any additional configuration to get the behavior described in the PR description.

[chris-oo]

Right. So there are a few things:
a) we do support features in both igvm_defs and igvm for unstable but we didn't gate the NATIVE VP context type correctly behind unstable
b) I don't see any makefile default enablement of the unstable feature. I'll need to dig a bit to see how QEMU is building if they're passing unstable or not.

Regardless, I think what you've said is reasonable. We can't really undo what we've published without breaking things, unfortunately.

[jethrogb]

a) we do support features in both igvm_defs and igvm for unstable

I'm not sure what you mean by this. Yes, it's there for igvm_defs, but here is the current [features] section from the igvm Cargo.toml

[chris-oo]

Ah I see now. See the usage of the igvm_defs dep:

[dependencies]
igvm_defs = { workspace = true, features = ["unstable"] }

What this means is you always get all the unstable headers. Which, is what was required for QEMU support to be useful at all from what I remember.

Regardless, I think that we will very soon promote all current unstable headers and stabilize the V2 version.