[PATCH v3 4/4] KVM: arm64: Clear active_vmids on vCPU schedule out

[Shameer Kolothum]

Like ASID allocator, we copy the active_vmids into the
reserved_vmids on a rollover. But it's unlikely that
every CPU will have a vCPU as current task and we may
end up unnecessarily reserving the VMID space.

Hence, clear active_vmids when scheduling out a vCPU.

Suggested-by: Will Deacon <will@xxxxxxxxxx>
Signed-off-by: Shameer Kolothum <shameerali.kolothum.thodi@xxxxxxxxxx>
---
 arch/arm64/include/asm/kvm_host.h | 1 +
 arch/arm64/kvm/arm.c              | 1 +
 arch/arm64/kvm/vmid.c             | 6 ++++++
 3 files changed, 8 insertions(+)

diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index bb993bce1363..d93141cb8d16 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -687,6 +687,7 @@ extern unsigned int kvm_arm_vmid_bits;
 int kvm_arm_vmid_alloc_init(void);
 void kvm_arm_vmid_alloc_free(void);
 void kvm_arm_vmid_update(struct kvm_vmid *kvm_vmid);
+void kvm_arm_vmid_clear_active(void);
 
 static inline void kvm_arm_pvtime_vcpu_init(struct kvm_vcpu_arch *vcpu_arch)
 {
diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index 077e55a511a9..b134a1b89c84 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -435,6 +435,7 @@ void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
 	kvm_timer_vcpu_put(vcpu);
 	kvm_vgic_put(vcpu);
 	kvm_vcpu_pmu_restore_host(vcpu);
+	kvm_arm_vmid_clear_active();
 
 	vcpu->cpu = -1;
 }
diff --git a/arch/arm64/kvm/vmid.c b/arch/arm64/kvm/vmid.c
index 5584e84aed95..5fd51f5445c1 100644
--- a/arch/arm64/kvm/vmid.c
+++ b/arch/arm64/kvm/vmid.c
@@ -116,6 +116,12 @@ static u64 new_vmid(struct kvm_vmid *kvm_vmid)
 	return idx2vmid(vmid) | generation;
 }
 
+/* Call with preemption disabled */
+void kvm_arm_vmid_clear_active(void)
+{
+	atomic64_set(this_cpu_ptr(&active_vmids), 0);
+}
+
 void kvm_arm_vmid_update(struct kvm_vmid *kvm_vmid)
 {
 	unsigned long flags;
-- 
2.17.1