[PATCH v2 0/9] KVM/hostmem: Support init-shared guest-memfd as VM backends

[Peter Xu <peterx@redhat.com>]

NOTE: The test cases of this series needs a dependency small series:

Based-on: <20251117223908.415965-1-peterx@redhat.com>

[PATCH 0/4] tests/migration-test: Introduce mem_type
https://lore.kernel.org/r/20251117223908.415965-1-peterx@redhat.com

v2 changelog:
- Linux-header update patch dropped because a similar version has landed
- Replaced old patch 2 with a similar but better one from Xiaoyao Li
- Target this series for QEMU 11.0 (hence, update in qapi/ "Since:")
- Added a qtest covering guest-memfd boot and basic precopy migration
- Fix checkpatch issues

=========8<===========

This series allows QEMU to consume init-shared guest-memfd to be a common
memory backend. Before this series, guest-memfd was only used in CoCo and
the fds will be created implicitly whenever CoCo environment is detected.
When used in init-shared mode, the guest-memfd will be specified in the
command lines directly just like other types of memory backends.

In the current patchset, I reused the memory-backend-memfd object, rather
than creating a new type of object.  After all, guest-memfd (at least from
userspace POV) works similarly like a memfd, except that it was tailored
for VM's use case.

This approach so far also does not involve gmem bindings to KVM instances,
hence it is not prone to issues when the same chunk of RAM will be attached
to more than one KVM memslots.

Now, instead of using a normal memfd backend using:

  -object memory-backend-memfd,id=ID,size=SIZE,share=on

One can also boot a VM with guest-memfd:

  -object memory-backend-memfd,id=ID,size=SIZE,share=on,guest-memfd=on

The init-shared guest-memfd relies on almost the latest linux, as the
mmap() support just landed v6.18-rc2.  When run it on an older qemu, we'll
see errors like:

  qemu-system-x86_64: KVM does not support guest_memfd

One thing to mention is live migration is by default supported, however
postcopy is still currently not supported.  The postcopy support will have
some kernel dependency work to be merged in Linux first.

Thanks,

Peter Xu (8):
  kvm: Detect guest-memfd flags supported
  memory: Rename RAM_GUEST_MEMFD to RAM_GUEST_MEMFD_PRIVATE
  memory: Rename memory_region_has_guest_memfd() to *_private()
  ramblock: Rename guest_memfd to guest_memfd_private
  hostmem: Rename guest_memfd to guest_memfd_private
  hostmem: Support in-place guest memfd to back a VM
  tests/migration-test: Support guest-memfd init shared mem type
  tests/migration-test: Add a precopy test for guest-memfd

Xiaoyao Li (1):
  kvm: Decouple memory attribute check from kvm_guest_memfd_supported

 qapi/qom.json                         |  6 ++-
 include/system/hostmem.h              |  2 +-
 include/system/kvm.h                  |  1 +
 include/system/memory.h               | 17 +++----
 include/system/ram_addr.h             |  2 +-
 include/system/ramblock.h             |  7 ++-
 tests/qtest/migration/framework.h     |  4 ++
 accel/kvm/kvm-all.c                   | 27 ++++++++---
 accel/stubs/kvm-stub.c                |  5 ++
 backends/hostmem-file.c               |  2 +-
 backends/hostmem-memfd.c              | 68 +++++++++++++++++++++++++--
 backends/hostmem-ram.c                |  2 +-
 backends/hostmem-shm.c                |  2 +-
 backends/hostmem.c                    |  2 +-
 system/memory.c                       |  7 +--
 system/physmem.c                      | 37 +++++++++------
 tests/qtest/migration/framework.c     | 60 +++++++++++++++++++++++
 tests/qtest/migration/precopy-tests.c | 12 +++++
 18 files changed, 219 insertions(+), 44 deletions(-)

-- 
2.50.1