Make unused states of Reserved unrepresentable

[Vanille-N]

In the previous TB update we discovered that the existence of Reserved + !ty_is_freeze + protected is undesirable.

This has the side effect of making Reserved { conflicted: true, ty_is_freeze: false } unreachable.
As such it is desirable that this state would also be unrepresentable.

This PR eliminates the unused configuration by changing

enum PermissionPriv {
    Reserved { ty_is_freeze: bool, conflicted: bool },
    ...
}

into

enum PermissionPriv {
    ReservedFrz { conflicted: bool },
    ReservedIM,
    ...
}

but this is not the only solution and Reserved(Activable | Conflicted | InteriorMut) could be discussed.
In addition to making the unreachable state not representable anymore, this change has the nice side effect of enabling foreign_read to no longer depend explicitly on the protected flag.

Currently waiting for

• @JoJoDeveloping to confirm that this is the same representation of Reserved as what is being implemented in simuliris,
• @RalfJung to approve that this does not introduce too much overhead in the trusted codebase.

[JoJoDeveloping]

confirm that this is the same representation of Reserved as what is being implemented in simuliris

Indeed, I can confirm:

[RalfJung]

It doesn't seem obvious that merging the two states would make things so much simpler, so -- fine for me to split up the states like this.

[RalfJung]

@rustbot author

[Vanille-N]

@rustbot ready

[Vanille-N]

It was a good idea to add the assert!(!protected), it led me to discover a few more cases of exhaustive tests exploring too many initial states.

[RalfJung]

Looks good, thanks. :)

Please squash the commits.

[RalfJung]

Sorry, I missed this one since GH doesn't send notifications on force pushes.^^ Please always post a message in the PR when it is now waiting on me to do something again. :)

@bors r+

[bors]

📌 Commit ae183fd has been approved by RalfJung

It is now in the queue for this repository.

[bors]

⌛ Testing commit ae183fd with merge eeb6e96...

[bors]

☀️ Test successful - checks-actions
Approved by: RalfJung
Pushing eeb6e96 to master...