Virtual Memory and Caches

This is a part of the Memory Subsystem.

Caches and Addressing

The process issues a virtual address (VA) in connection with a memory access. The memory subsystem deals with physical addresses (PAs). The virtual memory subsystem in the OS performs the $\text{VA}\to \text{PA}$ translation.

Caches perform two functions to identify a hit/miss:

1. Indexing
2. Tag matching

How does address translation interact with data caching?

Generally, it is preferred to use the VIPT variant in L1 caches because the index is available pre-translation.

Issues to Consider

Flushing of caches on a context switch: use PID as part of the tag.

Aliasing: two different VAs for the same PA.

• Use page coloring (“set associative mapping for VM”)

MMIO

• Typically uses physical addresses