CS-3310 - 07 Virtualization - Memory

Why is memory virtualization difficult?

Guest OS believes it controls physical memory.

What is the guest's “physical” memory called?

Guest physical memory.

What is the machine's actual memory called?

Host physical memory.

What is the purpose of shadow page tables?

Map guest virtual -> host physical addresses.

When must shadow page tables be updated?

Whenever guest OS updates its own tables.

What is a guest-induced page fault?

Page fault generated by the guest OS.

What is a hypervisor-induced page fault?

Fault triggered to maintain shadow consistency.

Why are page faults expensive in VMs?

require VM exits and hypervisor work.

What is overcommitment?

Hypervisor allocates more VM memory than physically exists.

What is deduplication?

Sharing identical memory pages among VMs.

What is ballooning?

Hypervisor reclaiming memory via a balloon driver inside the VM.

How does ballooning reduce VM memory?

Inflated balloon forces guest to free pages.

What hardware assists memory virtualization?

Nested page tables (SLAT / EPT).

What do EPT/SLAT add?

Hardware mapping of guest physical -> host physical.

What is guest virtual → host physical translation via EPT?

Hardware walks guest tables, then nested tables.

Why do EPT/SLAT improve performance?

Reduce VM exits during address translation.

What are the three levels of memory addressing with virtualization?

Guest virtual, guest physical, host physical.