[PATCH] LoongArch: KVM: Reload one-shot TVAL on migration destination

[Tao Cui <cui.tao@linux.dev>]

From: Tao Cui <cuitao@kylinos.cn>

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 guest observes a premature timer event right
after migration.

The expired one-shot case (TVAL = -1) is already handled earlier, so only
the non-expired one-shot path is affected. When expire has not been set
(i.e. on the destination), reload the remaining countdown from the
migrated TVAL. The regular preempt/resume path on the source, where
expire is valid, is unchanged.

Fixes: a5857b9ff6e0 ("LoongArch: KVM: Implement vcpu timer operations")
Signed-off-by: Tao Cui <cuitao@kylinos.cn>
---
 arch/loongarch/kvm/timer.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/loongarch/kvm/timer.c b/arch/loongarch/kvm/timer.c
index 3829f35a4070..57f53d19a00a 100644
--- a/arch/loongarch/kvm/timer.c
+++ b/arch/loongarch/kvm/timer.c
@@ -132,6 +132,14 @@ void kvm_restore_timer(struct kvm_vcpu *vcpu)
 		 * during injecting intr async
 		 */
 		kvm_queue_irq(vcpu, INT_TI);
+	} else if (!expire) {
+		/*
+		 * One-shot timer on the migration destination: vcpu->arch.expire
+		 * is host-internal and is not migrated, so it is still 0 here.
+		 * Reload the remaining countdown from the migrated TVAL instead
+		 * of firing the timer immediately.
+		 */
+		delta = ticks;
 	}
 
 	write_gcsr_timertick(delta);
-- 
2.43.0