My understanding of memaccess is that it
provides the following functionality:
1. Modify
permission values in the page table of the target domain.
2. When the
domain generates an illegal access, the exception handler
delegates to memaccess, which pauses the VCPU and records the
event in a ring buffer.
3. Some
permission values are special in that they automatically
mutate to a different value following the first access; others
are persistently applied.
We would like to use memaccess to perform
(1) - but rather than pausing the VCPU in (2), instead simply
directly inject the exception into the VCPU. I can see two
ways of doing this:
a) Implement an
observer of the ring buffer, which triggers injection of the
exception and unpausing of the VCPU.
b) Define new
xenmem_access_t values which cause the exception handler to
reinject rather than adding a message to the ring buffer.
(a) seems cumbersome, and requires multiple
context switches in order to handle the exception.
(b) therefore looks preferable, and I think
should be fairly simple to implement on top of
https://github.com/tklengyel/xen/tree/arm_memaccess15.
Does this sound reasonable? Or is there a
better way of modifying access permissions for a specific pfn
range of a target domain?
