[v5 1/3] KVM: setup empty irq routing when create vm

[Yi Wang <up2wing@gmail.com>]

From: Yi Wang <foxywang@tencent.com>

Add a new function to setup empty irq routing in kvm path, which
can be invoded in non-architecture-specific functions. The difference
compared to the kvm_setup_empty_irq_routing() is this function just
alloc the empty irq routing and does not need synchronize srcu, as
we will call it in kvm_create_vm().

Using the new adding function, we can setup empty irq routing when
kvm_create_vm(), so that x86 and s390 no longer need to set
empty/dummy irq routing when creating an IRQCHIP 'cause it avoid
an synchronize_srcu.

Signed-off-by: Yi Wang <foxywang@tencent.com>
---
 include/linux/kvm_host.h |  2 ++
 virt/kvm/irqchip.c       | 23 +++++++++++++++++++++++
 virt/kvm/kvm_main.c      |  9 ++++++++-
 3 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 48f31dcd318a..a5f12b667ca5 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -2100,6 +2100,7 @@ int kvm_set_irq_routing(struct kvm *kvm,
 			const struct kvm_irq_routing_entry *entries,
 			unsigned nr,
 			unsigned flags);
+int kvm_init_irq_routing(struct kvm *kvm);
 int kvm_set_routing_entry(struct kvm *kvm,
 			  struct kvm_kernel_irq_routing_entry *e,
 			  const struct kvm_irq_routing_entry *ue);
@@ -2108,6 +2109,7 @@ void kvm_free_irq_routing(struct kvm *kvm);
 #else
 
 static inline void kvm_free_irq_routing(struct kvm *kvm) {}
+int kvm_init_irq_routing(struct kvm *kvm) {}
 
 #endif
 
diff --git a/virt/kvm/irqchip.c b/virt/kvm/irqchip.c
index 1e567d1f6d3d..ec1fda7fffea 100644
--- a/virt/kvm/irqchip.c
+++ b/virt/kvm/irqchip.c
@@ -237,3 +237,26 @@ int kvm_set_irq_routing(struct kvm *kvm,
 
 	return r;
 }
+
+/*
+ * Alloc empty irq routing.
+ * Called only during vm creation, because we don't synchronize_srcu here.
+ */
+int kvm_init_irq_routing(struct kvm *kvm)
+{
+	struct kvm_irq_routing_table *new;
+	int chip_size;
+
+	new = kzalloc(struct_size(new, map, 1), GFP_KERNEL_ACCOUNT);
+	if (!new)
+		return -ENOMEM;
+
+	new->nr_rt_entries = 1;
+
+	chip_size = sizeof(int) * KVM_NR_IRQCHIPS * KVM_IRQCHIP_NUM_PINS;
+	memset(new->chip, -1, chip_size);
+
+	RCU_INIT_POINTER(kvm->irq_routing, new);
+
+	return 0;
+}
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index ff0a20565f90..4100ebdd14fe 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1233,6 +1233,11 @@ static struct kvm *kvm_create_vm(unsigned long type, const char *fdname)
 		goto out_err_no_irq_srcu;
 
 	refcount_set(&kvm->users_count, 1);
+
+	r = kvm_init_irq_routing(kvm);
+	if (r)
+		goto out_err_no_irq_routing;
+
 	for (i = 0; i < kvm_arch_nr_memslot_as_ids(kvm); i++) {
 		for (j = 0; j < 2; j++) {
 			slots = &kvm->__memslots[i][j];
@@ -1308,9 +1313,11 @@ static struct kvm *kvm_create_vm(unsigned long type, const char *fdname)
 out_err_no_disable:
 	kvm_arch_destroy_vm(kvm);
 out_err_no_arch_destroy_vm:
-	WARN_ON_ONCE(!refcount_dec_and_test(&kvm->users_count));
 	for (i = 0; i < KVM_NR_BUSES; i++)
 		kfree(kvm_get_bus(kvm, i));
+	kvm_free_irq_routing(kvm);
+out_err_no_irq_routing:
+	WARN_ON_ONCE(!refcount_dec_and_test(&kvm->users_count));
 	cleanup_srcu_struct(&kvm->irq_srcu);
 out_err_no_irq_srcu:
 	cleanup_srcu_struct(&kvm->srcu);
-- 
2.39.3