RFC: https://bugzilla.tianocore.org/show_bug.cgi?id=3429
TdxDxe driver is dispatched early in DXE, due to being list in APRIORI.
This module is responsible for below features:
- Sets max logical cpus based on TDINFO
- Sets PCI PCDs based on resource hobs
- Set shared bit in MMIO region
- Relocate Td mailbox and set its address in MADT table.
1. Set shared bit in MMIO region
Qemu allows a ROM device to set to ROMD mode (default) or MMIO mode.
When it is in ROMD mode, the device is mapped to guest memory and
satisfies read access directly.
In EDK2 Option ROM is treated as MMIO region. So Tdx guest access
Option ROM via TDVMCALL(MMIO). But as explained above, since Qemu set
the Option ROM to ROMD mode, the call of TDVMCALL(MMIO) always return
INVALID_OPERAND. Tdvf then falls back to direct access. This requires
to set the shared bit to corresponding PageTable entry. Otherwise it
triggers GP fault.
TdxDxe's entry point is the right place to set the shared bit in MMIO
region because Option ROM has not been discoverd yet.
2. Relocate Td mailbox and set the new address in MADT Mutiprocessor
Wakeup Table.
In TDX the guest firmware is designed to publish a multiprocessor-wakeup
structure to let the guest-bootstrap processor wake up guest-application
processors with a mailbox. The mailbox is memory that the guest firmware
can reserve so each guest virtual processor can have the guest OS send
a message to them. The address of the mailbox is recorded in the MADT
table. See [ACPI].
TdxDxe registers for protocol notification
(gQemuAcpiTableNotifyProtocolGuid) to call the AlterAcpiTable(), in
which MADT table is altered by the above Mailbox address. The protocol
will be installed in AcpiPlatformDxe when the MADT table provided by
Qemu is ready. This is to maintain the simplicity of the AcpiPlatformDxe.
AlterAcpiTable is the registered function which traverses the ACPI
table list to find the original MADT from Qemu. After the new MADT is
configured and installed, the original one will be uninstalled.
[ACPI] https://uefi.org/specs/ACPI/6.4/05_ACPI_Software_Programming_Model
/ACPI_Software_Programming_Model.html#multiprocessor-wakeup-structure
Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
Cc: Jordan Justen <jordan.l.justen@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>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Acked-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Jiewen Yao <jiewen.yao@intel.com>
Signed-off-by: Min Xu <min.m.xu@intel.com>
Min Xu