Commit fbe4a7e8 authored by Yi Wang's avatar Yi Wang Committed by Sean Christopherson
Browse files

KVM: Setup empty IRQ routing when creating a VM 



Setup empty IRQ routing during VM creation so that x86 and s390 don't need
to set empty/dummy IRQ routing during KVM_CREATE_IRQCHIP (in future
patches).  Initializing IRQ routing before there are any potential readers
allows KVM to avoid the synchronize_srcu() in kvm_set_irq_routing(), which
can introduces 20+ milliseconds of latency in the VM creation path.

Ensuring that all VMs have non-NULL IRQ routing also hardens KVM against
misbehaving userspace VMMs, e.g. RISC-V dynamically instantiates its
interrupt controller, but doesn't override kvm_arch_intc_initialized() or
kvm_arch_irqfd_allowed(), and so can likely reach kvm_irq_map_gsi()
without fully initialized IRQ routing.

Signed-off-by: default avatarYi Wang <foxywang@tencent.com>
Acked-by: default avatarChristian Borntraeger <borntraeger@linux.ibm.com>
Link: https://lore.kernel.org/r/20240506101751.3145407-2-foxywang@tencent.com


[sean: init refcount after IRQ routing, fix stub, massage changelog]
Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
parent f2362c04

include/linux/kvm_host.h

+6 −0
Original line number Diff line number Diff line
@@ -2094,6 +2094,7 @@ 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);
@@ -2103,6 +2104,11 @@ void kvm_free_irq_routing(struct kvm *kvm); 


static inline void kvm_free_irq_routing(struct kvm *kvm) {}



static inline int kvm_init_irq_routing(struct kvm *kvm)

{

	return 0;

}



#endif



int kvm_send_userspace_msi(struct kvm *kvm, struct kvm_msi *msi);

virt/kvm/irqchip.c

+24 −0
Original line number Diff line number Diff line
@@ -237,3 +237,27 @@ int kvm_set_irq_routing(struct kvm *kvm, 


	return r;

}



/*

 * Allocate empty IRQ routing by default so that additional setup isn't needed

 * when userspace-driven IRQ routing is activated, and so that kvm->irq_routing

 * is guaranteed to be non-NULL.

 */

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;

}

virt/kvm/kvm_main.c

+7 −0
Original line number Diff line number Diff line
@@ -1186,7 +1186,12 @@ static struct kvm *kvm_create_vm(unsigned long type, const char *fdname) 
	if (init_srcu_struct(&kvm->irq_srcu))

		goto out_err_no_irq_srcu;



	r = kvm_init_irq_routing(kvm);

	if (r)

		goto out_err_no_irq_routing;



	refcount_set(&kvm->users_count, 1);



	for (i = 0; i < kvm_arch_nr_memslot_as_ids(kvm); i++) {

		for (j = 0; j < 2; j++) {

			slots = &kvm->__memslots[i][j];
@@ -1265,6 +1270,8 @@ static struct kvm *kvm_create_vm(unsigned long type, const char *fdname) 
	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:

	cleanup_srcu_struct(&kvm->irq_srcu);

out_err_no_irq_srcu:

	cleanup_srcu_struct(&kvm->srcu);