[PATCH v2] 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 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. The regular preempt/resume
path on the source, where expire is valid, is unchanged.

Suggested-by: Bibo Mao <maobibo@loongson.cn>
Fixes: a5857b9ff6e0 ("LoongArch: KVM: Implement vcpu timer operations")
Signed-off-by: Tao Cui <cuitao@kylinos.cn>

---

Changes in v2:
- Move the expire check before ktime_before() (suggested by Bibo Mao)
- Remove the old else-if branch that was one-shot only.

---
 arch/loongarch/kvm/timer.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/arch/loongarch/kvm/timer.c b/arch/loongarch/kvm/timer.c
index 3829f35a4070..08359a612bde 100644
--- a/arch/loongarch/kvm/timer.c
+++ b/arch/loongarch/kvm/timer.c
@@ -119,6 +119,17 @@ 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.
+		 */
+		if (ticks < cfg)
+			delta = tick_to_ns(vcpu, ticks);
+		expire = ktime_add_ns(ktime_get(), delta);
+	}
+
 	if (ktime_before(now, expire))
 		delta = ktime_to_tick(vcpu, ktime_sub(expire, now));
 	else if (cfg & CSR_TCFG_PERIOD) {
-- 
2.43.0