linux-kernel - [PATCH v3 0/5] Introduce movable pages for Hyper-V guests

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Message-ID: 
 <175942263069.128138.16103948906881178993.stgit@skinsburskii-cloud-desktop.internal.cloudapp.net>
Date: Thu, 02 Oct 2025 16:35:44 +0000
From: Stanislav Kinsburskii <skinsburskii@...ux.microsoft.com>
To: kys@...rosoft.com, haiyangz@...rosoft.com, wei.liu@...nel.org,
 decui@...rosoft.com
Cc: linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v3 0/5] Introduce movable pages for Hyper-V guests

>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(-)