KVM: arm64: Reload stage-2 for VMID change on VHE

Naturally, a change to the VMID for an MMU implies a new value for
VTTBR. Reload on VMID change in anticipation of loading stage-2 on
vcpu_load() instead of every guest entry.

Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20231018233212.2888027-4-oliver.upton@linux.dev
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>

Author: Marc Zyngier

arch/arm64/include/asm/kvm_host.h

@@ -1025,7 +1025,7 @@ int kvm_arm_pvtime_has_attr(struct kvm_vcpu *vcpu,
 extern unsigned int __ro_after_init kvm_arm_vmid_bits;
 int __init kvm_arm_vmid_alloc_init(void);
 void __init kvm_arm_vmid_alloc_free(void);
-void kvm_arm_vmid_update(struct kvm_vmid *kvm_vmid);
+bool 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)

arch/arm64/kvm/arm.c

@@ -950,7 +950,10 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
 		 * making a thread's VMID inactive. So we need to call
 		 * kvm_arm_vmid_update() in non-premptible context.
 		 */
-		kvm_arm_vmid_update(&vcpu->arch.hw_mmu->vmid);
+		if (kvm_arm_vmid_update(&vcpu->arch.hw_mmu->vmid) &&
+		    has_vhe())
+			__load_stage2(vcpu->arch.hw_mmu,
+				      vcpu->arch.hw_mmu->arch);
 
 		kvm_pmu_flush_hwstate(vcpu);
 

arch/arm64/kvm/vmid.c

@@ -135,10 +135,11 @@ void kvm_arm_vmid_clear_active(void)
 	atomic64_set(this_cpu_ptr(&active_vmids), VMID_ACTIVE_INVALID);
 }
 
-void kvm_arm_vmid_update(struct kvm_vmid *kvm_vmid)
+bool kvm_arm_vmid_update(struct kvm_vmid *kvm_vmid)
 {
 	unsigned long flags;
 	u64 vmid, old_active_vmid;
+	bool updated = false;
 
 	vmid = atomic64_read(&kvm_vmid->id);
 
@@ -156,17 +157,21 @@ void kvm_arm_vmid_update(struct kvm_vmid *kvm_vmid)
 	if (old_active_vmid != 0 && vmid_gen_match(vmid) &&
 	    0 != atomic64_cmpxchg_relaxed(this_cpu_ptr(&active_vmids),
 					  old_active_vmid, vmid))
-		return;
+		return false;
 
 	raw_spin_lock_irqsave(&cpu_vmid_lock, flags);
 
 	/* Check that our VMID belongs to the current generation. */
 	vmid = atomic64_read(&kvm_vmid->id);
-	if (!vmid_gen_match(vmid))
+	if (!vmid_gen_match(vmid)) {
 		vmid = new_vmid(kvm_vmid);
+		updated = true;
+	}
 
 	atomic64_set(this_cpu_ptr(&active_vmids), vmid);
 	raw_spin_unlock_irqrestore(&cpu_vmid_lock, flags);
+
+	return updated;
 }
 
 /*