[PATCH v3 0/5] KVM: arm64: fix VGICv3 redistributor rollback

[Karl Mehltretter <kmehltretter@gmail.com>]

A failed REDIST_REGION write can remove redistributor iodevs from
KVM_MMIO_BUS while leaving their cached vCPU assignments intact. A
corrected retry then skips those redistributors.

Userspace should instead see a failed region update atomically: no prior
redistributor assignment survives the failure, and the next successful
update rebuilds all possible assignments in region-index order.

Patch 1 fixes a separate accounting bug when an individual MMIO-bus
registration fails. It reserves the selected region slot before
registration and undoes that known-latest assignment if registration fails.

Patch 2 implements the atomic failed-region behavior. It unregisters every
redistributor iodev, clears every cached assignment, resets the region
counters, and frees the newly inserted region. An in-flight vCPU can have
an RD iodev before kvm_for_each_vcpu() can see it, so REDIST and
REDIST_REGION writes are serialized with vCPU creation and return -EBUSY
while the created_vcpus/online_vcpus counts differ.

Patch 3 is independent teardown cleanup. It separates MMIO-bus teardown
from config-locked assignment cleanup, preserves the cleanup required
before a late failed vCPU creation frees the vCPU, and removes the special
conditional from the common vCPU destructor.

Patch 4 keeps the selftest helper aligned with vm_create_with_vcpus(), and
patch 5 adds regression coverage for an overlapping region, retry, and
final GICR_TYPER accesses to all four redistributors. The test exercises
patch 2's final-state behavior; patch 1's MMIO-bus allocation failure is
not fault-injected.

Testing: built the patched kernel and the arm64 vgic_init selftest with
GCC 13.3.0 in an arm64 Linux container. The selftest passed under QEMU
11.0.2 TCG with -machine virt,virtualization=on,gic-version=3 and -cpu max.

---
Changes since v2:
- Patch 1: limit free_index rollback to the immediate registration failure
  under slots_lock instead of generic unregistration. (Sashiko)
- Patch 2: reset all assignments and region counters after a failed region
  update (Marc), and serialize REDIST and REDIST_REGION writes with vCPU
  creation so rollback cannot miss an unpublished assignment.
- Patch 3: add an already-locked unassignment primitive, move failed-vCPU
  cleanup to kvm_vgic_vcpu_destroy(), and remove the redundant base_addr
  reset. (Marc)
- Patch 4: match vm_create_with_vcpus() by using void * for the guest-code
  argument. (Sashiko)
- Patch 5: document how the first three redistributors span regions 0
  and 1; no functional change.

Previous version:
v2: https://lore.kernel.org/r/20260819224229.82948-1-kmehltretter@gmail.com

Karl Mehltretter (5):
  KVM: arm64: vgic-v3: Undo assignment on iodev registration failure
  KVM: arm64: vgic-v3: Reset redistributors after failed region setup
  KVM: arm64: vgic-v3: Separate redistributor teardown from unassignment
  KVM: arm64: selftests: Pass guest code to vm_gic_create_with_vcpus()
  KVM: arm64: selftests: Test VGICv3 redistributor region retry

 arch/arm64/kvm/vgic/vgic-init.c               |  46 +++----
 arch/arm64/kvm/vgic/vgic-kvm-device.c         |  20 +++
 arch/arm64/kvm/vgic/vgic-mmio-v3.c            |  83 ++++++++-----
 arch/arm64/kvm/vgic/vgic.h                    |   1 +
 tools/testing/selftests/kvm/arm64/vgic_init.c | 116 ++++++++++++++++--
 5 files changed, 200 insertions(+), 66 deletions(-)


base-commit: 57e7cf13ac26bf1a3dba6cfa601f7b2481811575
-- 
2.39.5 (Apple Git-154)