Hiding physical memory from OS and VT-d/IOMMU

["Tomas Pilar (tpilar)" <tpilar@solarflare.com>]

Hi,


I am trying to implement a message-box communication protocol between
PCIe devices in the same host without the assistance of the OS. For
irreducible reasons, I can't use PCIe endpoint-to-endpoint communication
so I thought I could create a DMA based message-box protocol where in
UEFI driver probe (during DXE) I blot out some physical memory (by
leaking a page of memory allocated as EfiRuntimeServicesData) that the
devices will then use to communicate even when the OS loads.


This runs into a problem when VT-d/IOMMU is involved because it still
stops the device from DMA into that page, even though the OS shouldn't
touch the page as it's been allocated using EfiRuntimeServicesData.


So my query is: Can I achieve this by allocating the box as a different
memory type (such as EfiUnusableMemory or EfiReservedMemoryType) and if
not, what would be a better way of doing this?


Cheers,

Tom

The information contained in this message is confidential and is intended for the addressee(s) only. If you have received this message in error, please notify the sender immediately and delete the message. Unless you are an addressee (or authorized to receive for an addressee), you may not use, copy or disclose to anyone this message or any information contained in this message. The unauthorized use, disclosure, copying or alteration of this message is strictly prohibited.