RFC: https://bugzilla.tianocore.org/show_bug.cgi?id=3429
Intel TDX architecture does not prescribe a specific software convention
to perform I/O from the guest TD. Guest TD providers have many choices to
provide I/O to the guest. The common I/O models are emulated devices,
para-virtualized devices, SRIOV devices and Direct Device assignments.
TDVF chooses para-virtualized I/O (Choice-A) which use the TDG.VP.VMCALL
function to invoke the funtions provided by the host VMM to perform I/O.
Another choice (Choice-B) is the emulation performed by the #VE handler.
There are 2 benefits of para-virtualized I/O:
1. Performance.
VMEXIT/VMENTRY is skipped so that the performance is better than #VE
handler.
2. De-couple with #VE handler.
Choice-B depends on the #VE handler which means I/O is not available
until #VE handler is installed. For example, in PEI phase #VE handler
is installed in CpuMpPei, while communication with Qemu (via I/O port)
happen earlier than it.
IoLibInternalTdx.c provides the helper functions for Tdx guest.
IoLibInternalTdxNull.c provides the null version of the helper functions.
It is included in the Non-X64 IoLib so that the build will not be broken.
Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Liming Gao <gaoliming@byosoft.com.cn>
Cc: Zhiguang Liu <zhiguang.liu@intel.com>
Cc: Brijesh Singh <brijesh.singh@amd.com>
Cc: Erdem Aktas <erdemaktas@google.com>
Cc: James Bottomley <jejb@linux.ibm.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Reviewed-by: Liming Gao <gaoliming@byosoft.com.cn>
Reviewed-by: Jiewen Yao <jiewen.yao@intel.com>
Signed-off-by: Min Xu <min.m.xu@intel.com>
Min Xu