This series adds batch register access support to QEMU's KVM GICv3
register synchronization path, reducing syscall overhead during
ARM64 live migration.

Currently, QEMU issues one ioctl per register when saving/restoring VGIC
state. On large VM configurations this means tens of thousands of syscalls,
where lock acquisition and context switch overhead dominates migration
downtime. Thus, we provide a batch register method to allow userspace
read/write multiple distributor and redistributor registers in a single call.
In this way, we can significantly reduce syscalls and migration downtime.

All batch paths probe kernel capability at runtime and fall back to the
original one-by-one path when the kernel does not support batch access,
ensuring backward compatibility.

This series depends on the corresponding kernel patches that add
KVM_DEV_ARM_VGIC_GRP_BATCH_REGS support.

Test the VM migration time under pressure conditions.
The VM specifications for migration are as follows:
- VM use 4-K page;
- the number of VCPU is 160;
- the total memory is 320Gigabit;
- use 'Redis SET-benchmark' to pressurize VM;

Performance results (3-run average, ms):

    | Metric              | Without patch | With patch | Improvement |
    |---------------------|---------------|------------|-------------|
    | Migration downtime  |        536    |     321    |     40%     |
    | Source (total)      |        344    |     230    |     33%     |
    |   - VGIC put        |        158    |      40    |     75%     |
    |   - VGIC get        |        120    |      19    |     84%     |
    | Destination (total) |        192    |      91    |     53%     |
    |   - VGIC put        |        132    |      27    |     80%     |

Yize Wang (4):
  Sync KVM ARM VGIC batch register UAPI to QEMU headers
  hw/intc/arm_gicv3_kvm: Add batch helper structures and functions
  hw/intc/arm_gicv3_kvm: Refactor kvm_arm_gicv3_put for batch register access
  hw/intc/arm_gicv3_kvm: Refactor kvm_arm_gicv3_get for batch register access

 hw/intc/arm_gicv3_kvm.c       | 1087 ++++++++++++++++++++++++++++++++++-------
 linux-headers/asm-arm64/kvm.h |    9 +
 2 files changed, 925 insertions(+), 171 deletions(-)

References:
[1] [PATCH 0/2] Batch register access for live migration optimization
    https://lore.kernel.org/kvmarm/20260918081930.4014735-1-wangyize7@huawei.com/T/#t