[RFC,v4,36/36] docs: Add TDX documentation

Add docs/system/i386/tdx.rst for TDX support, and add tdx in
confidential-guest-support.rst

Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
---
 docs/system/confidential-guest-support.rst |   1 +
 docs/system/i386/tdx.rst                   | 103 +++++++++++++++++++++
 docs/system/target-i386.rst                |   1 +
 3 files changed, 105 insertions(+)
 create mode 100644 docs/system/i386/tdx.rst

On Thu, May 12, 2022 at 11:18:03AM +0800,
Xiaoyao Li <xiaoyao.li@intel.com> wrote:

> Add docs/system/i386/tdx.rst for TDX support, and add tdx in
> confidential-guest-support.rst
> 
> Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
> ---
>  docs/system/confidential-guest-support.rst |   1 +
>  docs/system/i386/tdx.rst                   | 103 +++++++++++++++++++++
>  docs/system/target-i386.rst                |   1 +
>  3 files changed, 105 insertions(+)
>  create mode 100644 docs/system/i386/tdx.rst
> 
> diff --git a/docs/system/confidential-guest-support.rst b/docs/system/confidential-guest-support.rst
> index 0c490dbda2b7..66129fbab64c 100644
> --- a/docs/system/confidential-guest-support.rst
> +++ b/docs/system/confidential-guest-support.rst
> @@ -38,6 +38,7 @@ Supported mechanisms
>  Currently supported confidential guest mechanisms are:
>  
>  * AMD Secure Encrypted Virtualization (SEV) (see :doc:`i386/amd-memory-encryption`)
> +* Intel Trust Domain Extension (TDX) (see :doc:`i386/tdx`)
>  * POWER Protected Execution Facility (PEF) (see :ref:`power-papr-protected-execution-facility-pef`)
>  * s390x Protected Virtualization (PV) (see :doc:`s390x/protvirt`)
>  
> diff --git a/docs/system/i386/tdx.rst b/docs/system/i386/tdx.rst
> new file mode 100644
> index 000000000000..96d91fea5516
> --- /dev/null
> +++ b/docs/system/i386/tdx.rst
> @@ -0,0 +1,103 @@
> +Intel Trusted Domain eXtension (TDX)
> +====================================
> +
> +Intel Trusted Domain eXtensions (TDX) refers to an Intel technology that extends
> +Virtual Machine Extensions (VMX) and Multi-Key Total Memory Encryption (MKTME)
> +with a new kind of virtual machine guest called a Trust Domain (TD). A TD runs
> +in a CPU mode that is designed to protect the confidentiality of its memory
> +contents and its CPU state from any other software, including the hosting
> +Virtual Machine Monitor (VMM), unless explicitly shared by the TD itself.
> +
> +Prerequisites
> +-------------
> +
> +To run TD, the physical machine needs to have TDX module loaded and initialized
> +while KVM hypervisor has TDX support and has TDX enabled. If those requirements
> +are met, the ``KVM_CAP_VM_TYPES`` will report the support of ``KVM_X86_TDX_VM``.
> +
> +Trust Domain Virtual Firmware (TDVF)
> +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> +
> +Trust Domain Virtual Firmware (TDVF) is required to provide TD services to boot
> +TD Guest OS. TDVF needs to be copied to guest private memory and measured before
> +a TD boots.
> +
> +The VM scope ``MEMORY_ENCRYPT_OP`` ioctl provides command ``KVM_TDX_INIT_MEM_REGION``
> +to copy the TDVF image to TD's private memory space.
> +
> +Since TDX doesn't support readonly memslot, TDVF cannot be mapped as pflash
> +device and it actually works as RAM. "-bios" option is chosen to load TDVF.
> +
> +OVMF is the opensource firmware that implements the TDVF support. Thus the
> +command line to specify and load TDVF is `-bios OVMF.fd`
> +
> +Feature Control
> +---------------
> +
> +Unlike non-TDX VM, the CPU features (enumerated by CPU or MSR) of a TD is not
> +under full control of VMM. VMM can only configure part of features of a TD on
> +``KVM_TDX_INIT_VM`` command of VM scope ``MEMORY_ENCRYPT_OP`` ioctl.
> +
> +The configurable features have three types:
> +
> +- Attributes:
> +  - PKS (bit 30) controls whether Supervisor Protection Keys is exposed to TD,
> +  which determines related CPUID bit and CR4 bit;
> +  - PERFMON (bit 63) controls whether PMU is exposed to TD.
> +
> +- XSAVE related features (XFAM):
> +  XFAM is a 64b mask, which has the same format as XCR0 or IA32_XSS MSR. It
> +  determines the set of extended features available for use by the guest TD.
> +
> +- CPUID features:
> +  Only some bits of some CPUID leaves are directly configurable by VMM.
> +
> +What features can be configured is reported via TDX capabilities.
> +
> +TDX capabilities
> +~~~~~~~~~~~~~~~~
> +
> +The VM scope ``MEMORY_ENCRYPT_OP`` ioctl provides command ``KVM_TDX_CAPABILITIES``
> +to get the TDX capabilities from KVM. It returns a data structure of
> +``struct kvm_tdx_capabilites``, which tells the supported configuration of
> +attributes, XFAM and CPUIDs.
> +
> +Launching a TD (TDX VM)
> +-----------------------
> +
> +To launch a TDX guest:
> +
> +.. parsed-literal::
> +
> +    |qemu_system_x86| \\
> +        -machine ...,confidential-guest-support=tdx0 \\
> +        -object tdx-guest,id=tdx0 \\
> +        -bios OVMF.fd \\

Don't we need kernel-irqchip=split?
Or this patch series set it automatically?

Thanks,

> +
> +Debugging
> +---------
> +
> +Bit 0 of TD attributes, is DEBUG bit, which decides if the TD runs in off-TD
> +debug mode. When in off-TD debug mode, TD's VCPU state and private memory are
> +accessible via given SEAMCALLs. This requires KVM to expose APIs to invoke those
> +SEAMCALLs and resonponding QEMU change.
> +
> +It's targeted as future work.
> +
> +restrictions
> +------------
> +
> + - No readonly support for private memory;
> +
> + - No SMM support: SMM support requires manipulating the guset register states
> +   which is not allowed;
> +
> +Live Migration
> +--------------
> +
> +TODO
> +
> +References
> +----------
> +
> +- `TDX Homepage <https://www.intel.com/content/www/us/en/developer/articles/technical/intel-trust-domain-extensions.html>`__
> diff --git a/docs/system/target-i386.rst b/docs/system/target-i386.rst
> index 96bf54889a82..16dd4f1a8c80 100644
> --- a/docs/system/target-i386.rst
> +++ b/docs/system/target-i386.rst
> @@ -29,6 +29,7 @@ Architectural features
>     i386/kvm-pv
>     i386/sgx
>     i386/amd-memory-encryption
> +   i386/tdx
>  
>  .. _pcsys_005freq:
>  
> -- 
> 2.27.0
> 
>