KVM: arm64: vgic-v3: Roll back assignments from the new region

A failed REDIST_REGION write unregisters the redistributor iodevs of every
vCPU processed before the failure. This includes vCPUs assigned to older
regions. Their assignments remain cached, so a retry does not register the
iodevs again.

The vCPU whose registration fails has no assignment to roll back. For vCPUs
processed earlier, limit rollback to those assigned to the new region. The
region is removed on failure, so its free_index does not need restoring.

Resetting assignments from older regions is unsafe because a vCPU can own
one before kvm_for_each_vcpu() can see it. Rollback could then move
free_index behind that live assignment.

kvm_vgic_addr() holds slots_lock across the REDIST_REGION write. vCPU
creation takes the same lock before assigning a redistributor. A concurrent
vCPU cannot acquire an assignment from the new region before rollback
completes. The lock also keeps rdreg valid across the config_lock drop
required by MMIO-bus registration.

Fixes: c011f4ea106b ("KVM: arm/arm64: Check vcpu redist base before registering an iodev")
Cc: stable@vger.kernel.org
Assisted-by: Codex:gpt-5.6-sol
Signed-off-by: Karl Mehltretter <kmehltretter@gmail.com>
Link: https://patch.msgid.link/20260831081005.41346-3-kmehltretter@gmail.com
[maz: moved helper into the sole caller]
Signed-off-by: Marc Zyngier <maz@kernel.org>

0 files changed, 0 insertions, 0 deletions