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Add the VMM Communication Exception (#VC) to the InterruptDescriptorTable #313

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Nov 6, 2021
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Add the VMM Communication Exception (#VC) to the InterruptDescriptorTable #313

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a1fd7c3
Add the VMM Communication Exception (#VC) to the InterruptDescriptorT…
haraldh Oct 15, 2021
0e80711
Adjust vector number range in docs
phil-opp Nov 6, 2021
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36 changes: 33 additions & 3 deletions src/structures/idt.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -340,8 +340,37 @@ pub struct InterruptDescriptorTable {
/// vector nr. 20
pub virtualization: Entry<HandlerFunc>,

/// vector nr. 21-29
reserved_2: [Entry<HandlerFunc>; 9],
/// vector nr. 21-28
reserved_2: [Entry<HandlerFunc>; 8],

/// The VMM Communication Exception (`#VC`) is always generated by hardware when an `SEV-ES`
/// enabled guest is running and an `NAE` event occurs.
///
/// `SEV-ES` stands for the _"Encrypted State"_ feature of the _"AMD Secure Encrypted Virtualization"_
/// technology. `NAE` stands for an _"Non-Automatic Exit"_, which is an `VMEXIT` event that requires
/// hypervisor emulation. See
/// [this whitepaper](https://www.amd.com/system/files/TechDocs/Protecting%20VM%20Register%20State%20with%20SEV-ES.pdf)
/// for an overview of the `SEV-ES` feature.
///
/// The `#VC` exception is a precise, contributory, fault-type exception utilizing exception vector 29.
/// This exception cannot be masked. The error code of the `#VC` exception is equal
/// to the `#VMEXIT` code of the event that caused the `NAE`.
///
/// In response to a `#VC` exception, a typical flow would involve the guest handler inspecting the error
/// code to determine the cause of the exception and deciding what register state must be copied to the
/// `GHCB` (_"Guest Hypervisor Communication Block"_) for the event to be handled. The handler
/// should then execute the `VMGEXIT` instruction to
/// create an `AE` and invoke the hypervisor. After a later `VMRUN`, guest execution will resume after the
/// `VMGEXIT` instruction where the handler can view the results from the hypervisor and copy state from
/// the `GHCB` back to its internal state as needed.
///
/// Note that it is inadvisable for the hypervisor to set the `VMCB` (_"Virtual Machine Control Block"_)
/// intercept bit for the `#VC` exception as
/// this would prevent proper handling of `NAE`s by the guest. Similarly, the hypervisor should avoid
/// setting intercept bits for events that would occur in the `#VC` handler (such as `IRET`).
///
/// The vector number of the ``#VC`` exception is 29.
pub vmm_communication_exception: Entry<HandlerFuncWithErrCode>,

/// The Security Exception (`#SX`) signals security-sensitive events that occur while
/// executing the VMM, in the form of an exception so that the VMM may take appropriate
Expand Down Expand Up @@ -407,7 +436,8 @@ impl InterruptDescriptorTable {
machine_check: Entry::missing(),
simd_floating_point: Entry::missing(),
virtualization: Entry::missing(),
reserved_2: [Entry::missing(); 9],
reserved_2: [Entry::missing(); 8],
vmm_communication_exception: Entry::missing(),
security_exception: Entry::missing(),
reserved_3: Entry::missing(),
interrupts: [Entry::missing(); 256 - 32],
Expand Down