On Mon, May 18, 2026 at 06:21:18PM +0800, Meng Zhuo wrote:
> During KVM exit processing (KVM_PUT_RUNTIME_STATE), QEMU never modifies
> FP or Vector registers — only core GPRs/PC and CSRs are potentially
> changed. Re-syncing 32 FP and 32 Vector registers on every KVM exit
> wastes 36-68 individual KVM_SET_ONE_REG ioctls per vCPU exit.
>
> Follow the s390x pattern: early return on RUNTIME after syncing core
> registers and CSRs. KVM_PUT_FULL_STATE and KVM_PUT_RESET_STATE continue
> to sync everything for correctness during migration and initialization.
>
> Signed-off-by: Meng Zhuo <[email protected]>
Reviewed-by: Chao Liu <[email protected]>
Thanks,
Chao
> ---
> target/riscv/kvm/kvm-cpu.c | 19 ++++++++++++++-----
> 1 file changed, 14 insertions(+), 5 deletions(-)
>
> diff --git a/target/riscv/kvm/kvm-cpu.c b/target/riscv/kvm/kvm-cpu.c
> index b047ffa9c0..dd4193ea8b 100644
> --- a/target/riscv/kvm/kvm-cpu.c
> +++ b/target/riscv/kvm/kvm-cpu.c
> @@ -1385,6 +1385,17 @@ int kvm_arch_put_registers(CPUState *cs, KvmPutState
> level, Error **errp)
> return ret;
> }
>
> + /*
> + * For RUNTIME_STATE, KVM already has the correct FP and Vector state
> + * from the preceding KVM_RUN exit. QEMU never modifies these registers
> + * during exit handling, so re-syncing is unnecessary. This saves ~68
> + * KVM_SET_ONE_REG ioctls per vCPU exit. See also s390x which uses
> + * the same pattern.
> + */
> + if (KVM_PUT_RUNTIME_STATE == level) {
> + return ret;
> + }
> +
> ret = kvm_riscv_put_regs_fp(cs);
> if (ret) {
> return ret;
> @@ -1397,11 +1408,9 @@ int kvm_arch_put_registers(CPUState *cs, KvmPutState
> level, Error **errp)
>
> if (KVM_PUT_RESET_STATE == level) {
> RISCVCPU *cpu = RISCV_CPU(cs);
> - if (cs->cpu_index == 0) {
> - ret = kvm_riscv_sync_mpstate_to_kvm(cpu, KVM_MP_STATE_RUNNABLE);
> - } else {
> - ret = kvm_riscv_sync_mpstate_to_kvm(cpu, KVM_MP_STATE_STOPPED);
> - }
> + int state = cs->cpu_index == 0 ? KVM_MP_STATE_RUNNABLE
> + : KVM_MP_STATE_STOPPED;
> + ret = kvm_riscv_sync_mpstate_to_kvm(cpu, state);
> if (ret) {
> return ret;
> }
> --
> 2.47.3
>
>
