IRQ pseudocode needs to be able to access device I/O registers mapped at arbitrary address

[Jakub Jermář]

Currently, the IRQ pseudocode can only access device I/O registers that are accessible via the kernel identity mapping. However, some I/O registers are located on addresses that are out of the reach of the kernel identity mapping.

There have already been several proposals how to address this problem:

• implement some sort of non-identity mapping for kernel (must be locked in page tables)
• switch to the address space of the task which registered the pseudocode and use its userspace non-identity mapping

Note that all operations that take place during IRQ pseudocode execution, including possible TLB miss handling, may not carry out blocking operations (e.g. use passive synchronization primitives).