>From the start, the root-partition driver allocates, pins, and maps all
guest memory into the hypervisor at guest creation. This is simple: Linux
cannot move the pages, so the guest’s view in Linux and in Microsoft
Hypervisor never diverges.
However, this approach has major drawbacks:
- NUMA: affinity can’t be changed at runtime, so you can’t migrate guest memory
closer to the CPUs running it → performance hit.
- Memory management: unused guest memory can’t be swapped out, compacted, or
merged.
- Provisioning time: upfront allocation/pinning slows guest create/destroy.
- Overcommit: no memory overcommit on hosts with pinned-guest memory.
This series adds movable memory pages for Hyper-V child partitions. Guest
pages are no longer allocated upfront; they’re allocated and mapped into
the hypervisor on demand (i.e., when the guest touches a GFN that isn’t yet
backed by a host PFN).
When a page is moved, Linux no longer holds it and it is unmapped from the
hypervisor.
As a result, Hyper-V guests behave like regular Linux processes, enabling
standard Linux memory features to apply to guests.
Exceptions (still pinned):
1. Encrypted guests (explicit).
2. Guests with passthrough devices (implicitly pinned by the VFIO framework).
v3:
- Region is invalidated even if the mm has no users.
- Page remapping logic is updated to support 2M-unaligned remappings for
regions that are PMD-aligned, which can occur during both faults and
invalidations.
v2:
- Split unmap batching into a separate patch.
- Fixed commit messages from v1 review.
- Renamed a few functions for clarity.
---
Stanislav Kinsburskii (5):
Drivers: hv: Refactor and rename memory region handling functions
Drivers: hv: Centralize guest memory region destruction
Drivers: hv: Batch GPA unmap operations to improve large region
performance
Drivers: hv: Ensure large page GPA mapping is PMD-aligned
Drivers: hv: Add support for movable memory regions
drivers/hv/Kconfig | 1
drivers/hv/mshv_root.h | 10 +
drivers/hv/mshv_root_hv_call.c | 2
drivers/hv/mshv_root_main.c | 480 +++++++++++++++++++++++++++++++++-------
4 files changed, 410 insertions(+), 83 deletions(-)
