Re: [PATCH v3 1/2] LoongArch: KVM: Reload one-shot TVAL on migration destination

On 2026/7/15 下午6:06, Tao Cui wrote:
> From: Tao Cui <[email protected]>
> 
> kvm_restore_timer() rebuilds the remaining timer countdown from
> vcpu->arch.expire, which is host-internal and is not part of the migrated
> vCPU state. On the migration destination it is still 0, so for a one-shot
> timer that has not expired yet the computed delta is 0 and
> write_gcsr_timertick(0) injects the timer interrupt immediately instead of
> after the remaining time.
> 
> The expired one-shot case (TVAL = -1) is already handled earlier. When
> expire has not been set (i.e. on the migration destination), reload the
> remaining countdown from the migrated TVAL. This covers both one-shot and
> periodic timers. The regular preempt/resume path on the source, where
> expire is valid, is unchanged.
> 
> Suggested-by: Bibo Mao <[email protected]>
> Fixes: a5857b9ff6e0 ("LoongArch: KVM: Implement vcpu timer operations")
> Signed-off-by: Tao Cui <[email protected]>
> ---
>   arch/loongarch/kvm/timer.c | 12 ++++++++++++
>   1 file changed, 12 insertions(+)
> 
> diff --git a/arch/loongarch/kvm/timer.c b/arch/loongarch/kvm/timer.c
> index 3829f35a4070..96f33e34855a 100644
> --- a/arch/loongarch/kvm/timer.c
> +++ b/arch/loongarch/kvm/timer.c
> @@ -119,6 +119,18 @@ void kvm_restore_timer(struct kvm_vcpu *vcpu)
>   	delta = 0;
>   	now = ktime_get();
>   	expire = vcpu->arch.expire;
> +	if (!expire) {
> +		/*
> +		 * vcpu->arch.expire is host-internal and is not migrated,
> +		 * so it is 0 after migration. Reload the remaining countdown
> +		 * from the migrated TVAL. This covers both one-shot and
> +		 * periodic timers.
> +		 */
> +		if (ticks < cfg)
> +			delta = tick_to_ns(vcpu, ticks);
> +		expire = ktime_add_ns(now, delta);
> +	}
> +
>   	if (ktime_before(now, expire))
>   		delta = ktime_to_tick(vcpu, ktime_sub(expire, now));
>   	else if (cfg & CSR_TCFG_PERIOD) {
> 
Reviewed-by: Bibo Mao <[email protected]>