[v7,1/4] KVM: x86: Split the APIC from the rest of IRQCHIP.

Commit Message

Paolo Bonzini July 30, 2015, 8:21 a.m. UTC

On 30/07/2015 08:21, Steve Rutherford wrote:
> First patch in a series which enables the relocation of the
> PIC/IOAPIC to userspace.
> 
> Adds capability KVM_CAP_SPLIT_IRQCHIP;
> 
> KVM_CAP_SPLIT_IRQCHIP enables the construction of LAPICs without the
> rest of the irqchip.
> 
> Compile tested for x86.
> 
> Signed-off-by: Steve Rutherford <[e-mail]>
> Suggested-by: Andrew Honig <[e-mail]>
> ---
>  Documentation/virtual/kvm/api.txt | 15 +++++++++++++++
>  arch/x86/include/asm/kvm_host.h   |  2 ++
>  arch/x86/kvm/i8254.c              |  4 +++-
>  arch/x86/kvm/ioapic.h             |  8 ++++++++
>  arch/x86/kvm/irq.h                | 11 ++++++++++-
>  arch/x86/kvm/irq_comm.c           |  9 ++++++++-
>  arch/x86/kvm/lapic.c              |  6 ++++--
>  arch/x86/kvm/vmx.c                |  4 ++--
>  arch/x86/kvm/x86.c                | 25 +++++++++++++++++++++++--
>  include/linux/kvm_host.h          |  1 +
>  include/uapi/linux/kvm.h          |  1 +
>  11 files changed, 77 insertions(+), 9 deletions(-)
> 
> diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
> index a4ebcb7..b655024 100644
> --- a/Documentation/virtual/kvm/api.txt
> +++ b/Documentation/virtual/kvm/api.txt
> @@ -3620,6 +3620,21 @@ struct {
>  
>  KVM handlers should exit to userspace with rc = -EREMOTE.
>  
> +7.5 KVM_SPLIT_IRQCHIP
> +
> +Architectures: x86
> +Parameters: None
> +Returns: 0 on success, -1 on error
> +
> +Create a local apic for each processor in the kernel. With this capability
> +enabled, the userspace VMM is expected to emulate the IOAPIC and PIC.
> +
> +This supersedes KVM_CREATE_IRQCHIP, creating only local APICs, but no in kernel
> +IOAPIC or PIC. This also enables in kernel routing of interrupt requests.
> +
> +Fails if VCPU has already been created, or if the irqchip is already in the
> +kernel (i.e. KVM_CREATE_IRQCHIP has already been called).
> +
>  
>  8. Other capabilities.
>  ----------------------
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index d3e7a53..b4fdf0c 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -670,6 +670,8 @@ struct kvm_arch {
>  	bool boot_vcpu_runs_old_kvmclock;
>  
>  	u64 disabled_quirks;
> +
> +	bool irqchip_split;
>  };
>  
>  struct kvm_vm_stat {
> diff --git a/arch/x86/kvm/i8254.c b/arch/x86/kvm/i8254.c
> index f588eb7..08116ff 100644
> --- a/arch/x86/kvm/i8254.c
> +++ b/arch/x86/kvm/i8254.c
> @@ -35,6 +35,7 @@
>  #include <linux/kvm_host.h>
>  #include <linux/slab.h>
>  
> +#include "ioapic.h"
>  #include "irq.h"
>  #include "i8254.h"
>  #include "x86.h"
> @@ -333,7 +334,8 @@ static void create_pit_timer(struct kvm *kvm, u32 val, int is_period)
>  	struct kvm_kpit_state *ps = &kvm->arch.vpit->pit_state;
>  	s64 interval;
>  
> -	if (ps->flags & KVM_PIT_FLAGS_HPET_LEGACY)
> +	if (!ioapic_in_kernel(kvm) ||
> +	    ps->flags & KVM_PIT_FLAGS_HPET_LEGACY)
>  		return;
>  
>  	interval = muldiv64(val, NSEC_PER_SEC, KVM_PIT_FREQ);
> diff --git a/arch/x86/kvm/ioapic.h b/arch/x86/kvm/ioapic.h
> index bf36d66..a8842c0 100644
> --- a/arch/x86/kvm/ioapic.h
> +++ b/arch/x86/kvm/ioapic.h
> @@ -97,6 +97,14 @@ static inline struct kvm_ioapic *ioapic_irqchip(struct kvm *kvm)
>  	return kvm->arch.vioapic;
>  }
>  
> +static inline int ioapic_in_kernel(struct kvm *kvm)
> +{
> +	int ret;
> +
> +	ret = (ioapic_irqchip(kvm) != NULL);
> +	return ret;
> +}
> +
>  void kvm_rtc_eoi_tracking_restore_one(struct kvm_vcpu *vcpu);
>  bool kvm_apic_match_dest(struct kvm_vcpu *vcpu, struct kvm_lapic *source,
>  		int short_hand, unsigned int dest, int dest_mode);
> diff --git a/arch/x86/kvm/irq.h b/arch/x86/kvm/irq.h
> index 3d782a2..72af5a9 100644
> --- a/arch/x86/kvm/irq.h
> +++ b/arch/x86/kvm/irq.h
> @@ -83,13 +83,22 @@ static inline struct kvm_pic *pic_irqchip(struct kvm *kvm)
>  	return kvm->arch.vpic;
>  }
>  
> +static inline int irqchip_split(struct kvm *kvm)
> +{
> +	return kvm->arch.irqchip_split;
> +}
> +
>  static inline int irqchip_in_kernel(struct kvm *kvm)
>  {
> +	bool ret;
>  	struct kvm_pic *vpic = pic_irqchip(kvm);
>  
>  	/* Read vpic before kvm->irq_routing.  */
>  	smp_rmb();
> -	return vpic != NULL;
> +	ret = (vpic != NULL);
> +	ret |= irqchip_split(kvm);

The memory barrier must be after irqchip_split.

> +
> +	return ret;
>  }
>  
>  void kvm_pic_reset(struct kvm_kpic_state *s);
> diff --git a/arch/x86/kvm/irq_comm.c b/arch/x86/kvm/irq_comm.c
> index 9efff9e..67f6b62 100644
> --- a/arch/x86/kvm/irq_comm.c
> +++ b/arch/x86/kvm/irq_comm.c
> @@ -208,7 +208,7 @@ void kvm_free_irq_source_id(struct kvm *kvm, int irq_source_id)
>  		goto unlock;
>  	}
>  	clear_bit(irq_source_id, &kvm->arch.irq_sources_bitmap);
> -	if (!irqchip_in_kernel(kvm))
> +	if (!ioapic_in_kernel(kvm))
>  		goto unlock;
>  
>  	kvm_ioapic_clear_all(kvm->arch.vioapic, irq_source_id);
> @@ -328,3 +328,10 @@ int kvm_setup_default_irq_routing(struct kvm *kvm)
>  	return kvm_set_irq_routing(kvm, default_routing,
>  				   ARRAY_SIZE(default_routing), 0);
>  }
> +
> +static const struct kvm_irq_routing_entry empty_routing[] = {};
> +
> +int kvm_setup_empty_irq_routing(struct kvm *kvm)
> +{
> +	return kvm_set_irq_routing(kvm, empty_routing, 0, 0);
> +}
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index c158f46..2f486d8 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -209,7 +209,8 @@ out:
>  	if (old)
>  		kfree_rcu(old, rcu);
>  
> -	kvm_vcpu_request_scan_ioapic(kvm);
> +	if (!irqchip_split(kvm))

Might as well use ioapic_in_kernel here.

> +		kvm_vcpu_request_scan_ioapic(kvm);
>  }
>  
>  static inline void apic_set_spiv(struct kvm_lapic *apic, u32 val)
> @@ -1845,7 +1846,8 @@ void kvm_apic_post_state_restore(struct kvm_vcpu *vcpu,
>  		kvm_x86_ops->hwapic_isr_update(vcpu->kvm,
>  				apic_find_highest_isr(apic));
>  	kvm_make_request(KVM_REQ_EVENT, vcpu);
> -	kvm_rtc_eoi_tracking_restore_one(vcpu);
> +	if (!ioapic_in_kernel(vcpu->kvm))

This should not be negated.

> +		kvm_rtc_eoi_tracking_restore_one(vcpu);
>  }
>  
>  void __kvm_migrate_apic_timer(struct kvm_vcpu *vcpu)
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 7323ea8..3a9653f 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -948,7 +948,7 @@ static inline bool cpu_has_vmx_tpr_shadow(void)
>  
>  static inline bool vm_need_tpr_shadow(struct kvm *kvm)
>  {
> -	return (cpu_has_vmx_tpr_shadow()) && (irqchip_in_kernel(kvm));
> +	return (cpu_has_vmx_tpr_shadow()) && irqchip_in_kernel(kvm);
>  }
>  
>  static inline bool cpu_has_secondary_exec_ctrls(void)
> @@ -9486,7 +9486,7 @@ static void prepare_vmcs02(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12)
>  	/* vmcs12's VM_ENTRY_LOAD_IA32_EFER and VM_ENTRY_IA32E_MODE are
>  	 * emulated by vmx_set_efer(), below.
>  	 */
> -	vm_entry_controls_init(vmx, 
> +	vm_entry_controls_init(vmx,
>  		(vmcs12->vm_entry_controls & ~VM_ENTRY_LOAD_IA32_EFER &
>  			~VM_ENTRY_IA32E_MODE) |
>  		(vmcs_config.vmentry_ctrl & ~VM_ENTRY_IA32E_MODE));
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index c6c6e9c..8e40ddf 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -2459,6 +2459,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>  	case KVM_CAP_TSC_DEADLINE_TIMER:
>  	case KVM_CAP_ENABLE_CAP_VM:
>  	case KVM_CAP_DISABLE_QUIRKS:
> +	case KVM_CAP_SPLIT_IRQCHIP:
>  #ifdef CONFIG_KVM_DEVICE_ASSIGNMENT
>  	case KVM_CAP_ASSIGN_DEV_IRQ:
>  	case KVM_CAP_PCI_2_3:
> @@ -3566,6 +3567,26 @@ static int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
>  		kvm->arch.disabled_quirks = cap->args[0];
>  		r = 0;
>  		break;
> +	case KVM_CAP_SPLIT_IRQCHIP: {
> +		mutex_lock(&kvm->lock);
> +		r = -EEXIST;
> +		if (irqchip_in_kernel(kvm))
> +			goto split_irqchip_unlock;
> +		if (!irqchip_split(kvm)) {

This "if" must be true.

> +			if (atomic_read(&kvm->online_vcpus))
> +				goto split_irqchip_unlock;
> +			r = kvm_setup_empty_irq_routing(kvm);
> +			if (r)
> +				goto split_irqchip_unlock;
> +			/* Pairs with irqchip_in_kernel. */
> +			smp_wmb();
> +			kvm->arch.irqchip_split = true;
> +		}
> +		r = 0;
> +split_irqchip_unlock:
> +		mutex_unlock(&kvm->lock);
> +		break;
> +	}
>  	default:
>  		r = -EINVAL;
>  		break;
> @@ -3679,7 +3700,7 @@ long kvm_arch_vm_ioctl(struct file *filp,
>  		}
>  
>  		r = -ENXIO;
> -		if (!irqchip_in_kernel(kvm))
> +		if (!irqchip_in_kernel(kvm) || !ioapic_in_kernel(kvm))

You're using ioapic_in_kernel for the 8259 too.  Better test
!irqchip_in_kernel || irqchip_split here.

>  			goto get_irqchip_out;
>  		r = kvm_vm_ioctl_get_irqchip(kvm, chip);
>  		if (r)
> @@ -3703,7 +3724,7 @@ long kvm_arch_vm_ioctl(struct file *filp,
>  		}
>  
>  		r = -ENXIO;
> -		if (!irqchip_in_kernel(kvm))
> +		if (!irqchip_in_kernel(kvm) || !ioapic_in_kernel(kvm))

Same here.

>  			goto set_irqchip_out;
>  		r = kvm_vm_ioctl_set_irqchip(kvm, chip);
>  		if (r)
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 29c0c28..1867b83 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -1004,6 +1004,7 @@ static inline int mmu_notifier_retry(struct kvm *kvm, unsigned long mmu_seq)
>  #endif
>  
>  int kvm_setup_default_irq_routing(struct kvm *kvm);
> +int kvm_setup_empty_irq_routing(struct kvm *kvm);
>  int kvm_set_irq_routing(struct kvm *kvm,
>  			const struct kvm_irq_routing_entry *entries,
>  			unsigned nr,
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index 9ef19eb..e4304d0 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -818,6 +818,7 @@ struct kvm_ppc_smmu_info {
>  #define KVM_CAP_DISABLE_QUIRKS 116
>  #define KVM_CAP_X86_SMM 117
>  #define KVM_CAP_MULTI_ADDRESS_SPACE 118
> +#define KVM_CAP_SPLIT_IRQCHIP 119
>  
>  #ifdef KVM_CAP_IRQ_ROUTING
>  
> 

Please review this diff:


No need to resend.

Paolo
--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to [e-mail]
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Comments

Steve Rutherford July 30, 2015, 8:37 a.m. UTC | #1

On Thu, Jul 30, 2015 at 10:21:54AM +0200, Paolo Bonzini wrote:
> Please review this diff:
> 
> diff --git b/arch/x86/kvm/irq.h a/arch/x86/kvm/irq.h
> index 72af5a989a2e..975cf33ef306 100644
> --- b/arch/x86/kvm/irq.h
> +++ a/arch/x86/kvm/irq.h
> @@ -93,11 +90,11 @@ static inline int irqchip_split(struct kvm *kvm)
>  	bool ret;
>  	struct kvm_pic *vpic = pic_irqchip(kvm);
>  
> -	/* Read vpic before kvm->irq_routing.  */
> -	smp_rmb();
>  	ret = (vpic != NULL);
>  	ret |= irqchip_split(kvm);
>  
> +	/* Read vpic before kvm->irq_routing.  */
> +	smp_rmb();
>  	return ret;
>  }
>  
> diff --git b/arch/x86/kvm/lapic.c a/arch/x86/kvm/lapic.c
> index 2f486d8ecdae..a86324ca9cc3 100644
> --- b/arch/x86/kvm/lapic.c
> +++ a/arch/x86/kvm/lapic.c
> @@ -209,7 +209,7 @@ out:
>  	if (old)
>  		kfree_rcu(old, rcu);
>  
> -	if (!irqchip_split(kvm))
> +	if (ioapic_in_kernel(kvm))
>  		kvm_vcpu_request_scan_ioapic(kvm);
>  }
>  
> @@ -1846,7 +1846,7 @@ void kvm_apic_post_state_restore(struct kvm_vcpu *vcpu,
>  		kvm_x86_ops->hwapic_isr_update(vcpu->kvm,
>  				apic_find_highest_isr(apic));
>  	kvm_make_request(KVM_REQ_EVENT, vcpu);
> -	if (!ioapic_in_kernel(vcpu->kvm))
> +	if (ioapic_in_kernel(vcpu->kvm))
>  		kvm_rtc_eoi_tracking_restore_one(vcpu);
>  }
>  
> diff --git b/arch/x86/kvm/x86.c a/arch/x86/kvm/x86.c
> index 49a98608e3f6..5d2b8695732c 100644
> --- b/arch/x86/kvm/x86.c
> +++ a/arch/x86/kvm/x86.c
> @@ -3573,16 +3573,14 @@ static int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
>  		r = -EEXIST;
>  		if (irqchip_in_kernel(kvm))
>  			goto split_irqchip_unlock;
> -		if (!irqchip_split(kvm)) {
> -			if (atomic_read(&kvm->online_vcpus))
> -				goto split_irqchip_unlock;
> -			r = kvm_setup_empty_irq_routing(kvm);
> -			if (r)
> -				goto split_irqchip_unlock;
> -			/* Pairs with irqchip_in_kernel. */
> -			smp_wmb();
> -			kvm->arch.irqchip_split = true;
> -		}
> +		if (atomic_read(&kvm->online_vcpus))
> +			goto split_irqchip_unlock;
> +		r = kvm_setup_empty_irq_routing(kvm);
> +		if (r)
> +			goto split_irqchip_unlock;
> +		/* Pairs with irqchip_in_kernel. */
> +		smp_wmb();
> +		kvm->arch.irqchip_split = true;
This looks a bit non-sensical, but is overprepared for the introduction
IOAPIC hotplug, which two patches down the line. Changing it is fine,
you'll just need to merge the very same change back.

>  		r = 0;
>  split_irqchip_unlock:
>  		mutex_unlock(&kvm->lock);
> @@ -3701,7 +3699,7 @@ long kvm_arch_vm_ioctl(struct file *filp,
>  		}
>  
>  		r = -ENXIO;
> -		if (!irqchip_in_kernel(kvm) || !ioapic_in_kernel(kvm))
> +		if (!irqchip_in_kernel(kvm) || irqchip_split(kvm))
>  			goto get_irqchip_out;
>  		r = kvm_vm_ioctl_get_irqchip(kvm, chip);
>  		if (r)
> @@ -3725,7 +3723,7 @@ long kvm_arch_vm_ioctl(struct file *filp,
>  		}
>  
>  		r = -ENXIO;
> -		if (!irqchip_in_kernel(kvm) || !ioapic_in_kernel(kvm))
> +		if (!irqchip_in_kernel(kvm) || irqchip_split(kvm))
>  			goto set_irqchip_out;
>  		r = kvm_vm_ioctl_set_irqchip(kvm, chip);
>  		if (r)
> 
> No need to resend.
> 
> Paolo

Looks good.
--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to [e-mail]
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Paolo Bonzini July 30, 2015, 9:38 a.m. UTC | #2

On 30/07/2015 10:37, Steve Rutherford wrote:
> This looks a bit non-sensical, but is overprepared for the introduction
> IOAPIC hotplug, which two patches down the line. Changing it is fine,
> you'll just need to merge the very same change back.

By "IOAPIC hotplug" you mean changing the number of reserved routes?  Is
it necessary?  You could just reserve a bunch of routes depending on the
maximum number of IOAPICs.

And especially, is it documented? :)  The docs say "Fails [...] if the
irqchip is already in the kernel (i.e. KVM_CREATE_IRQCHIP has already
been called)".

As before, no need to resend patches for now.  Let's finish discussing
all pending points, then I'll push what I have to kvm.git and you can
test it with your VMM.  There should be time between this week and the next.

Paolo
--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to [e-mail]
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Steve Rutherford July 30, 2015, 9:19 p.m. UTC | #3

On Thu, Jul 30, 2015 at 11:38:20AM +0200, Paolo Bonzini wrote:
> 
> 
> On 30/07/2015 10:37, Steve Rutherford wrote:
> > This looks a bit non-sensical, but is overprepared for the introduction
> > IOAPIC hotplug, which two patches down the line. Changing it is fine,
> > you'll just need to merge the very same change back.
> 
> By "IOAPIC hotplug" you mean changing the number of reserved routes?  Is
> it necessary?  You could just reserve a bunch of routes depending on the
> maximum number of IOAPICs.
Hmm. Yeah, I think that might be cleaner. Thinking about it, I'm a bit nervous
about the idea of the number of reserved routes shrinking. We would have needed
to trigger an IOAPIC scan if the number of reserved routes changed.

Jan might have an opinion here.

> 
> And especially, is it documented? :)  The docs say "Fails [...] if the
> irqchip is already in the kernel (i.e. KVM_CREATE_IRQCHIP has already
> been called)".
The documentation was out of date D: 

> 
> As before, no need to resend patches for now.  Let's finish discussing
> all pending points, then I'll push what I have to kvm.git and you can
> test it with your VMM.  There should be time between this week and the next.
> 
> Paolo
--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to [e-mail]
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Jan Kiszka July 31, 2015, 8:32 a.m. UTC | #4

On 2015-07-30 23:19, Steve Rutherford wrote:
> On Thu, Jul 30, 2015 at 11:38:20AM +0200, Paolo Bonzini wrote:
>>
>>
>> On 30/07/2015 10:37, Steve Rutherford wrote:
>>> This looks a bit non-sensical, but is overprepared for the introduction
>>> IOAPIC hotplug, which two patches down the line. Changing it is fine,
>>> you'll just need to merge the very same change back.
>>
>> By "IOAPIC hotplug" you mean changing the number of reserved routes?  Is
>> it necessary?  You could just reserve a bunch of routes depending on the
>> maximum number of IOAPICs.
> Hmm. Yeah, I think that might be cleaner. Thinking about it, I'm a bit nervous
> about the idea of the number of reserved routes shrinking. We would have needed
> to trigger an IOAPIC scan if the number of reserved routes changed.
> 
> Jan might have an opinion here.

A static preallocation is likely fine, given reasonable room. I have no
idea about a good limit, though. To be safe, we could pull in someone
from Intel, maybe the guy who worked on the IOAPIC refactorings in the
kernel to enable hotplugging.

Jan

Patch

diff --git b/arch/x86/kvm/irq.h a/arch/x86/kvm/irq.h
index 72af5a989a2e..975cf33ef306 100644
--- b/arch/x86/kvm/irq.h
+++ a/arch/x86/kvm/irq.h
@@ -93,11 +90,11 @@  static inline int irqchip_split(struct kvm *kvm)
 	bool ret;
 	struct kvm_pic *vpic = pic_irqchip(kvm);
 
-	/* Read vpic before kvm->irq_routing.  */
-	smp_rmb();
 	ret = (vpic != NULL);
 	ret |= irqchip_split(kvm);
 
+	/* Read vpic before kvm->irq_routing.  */
+	smp_rmb();
 	return ret;
 }
 
diff --git b/arch/x86/kvm/lapic.c a/arch/x86/kvm/lapic.c
index 2f486d8ecdae..a86324ca9cc3 100644
--- b/arch/x86/kvm/lapic.c
+++ a/arch/x86/kvm/lapic.c
@@ -209,7 +209,7 @@  out:
 	if (old)
 		kfree_rcu(old, rcu);
 
-	if (!irqchip_split(kvm))
+	if (ioapic_in_kernel(kvm))
 		kvm_vcpu_request_scan_ioapic(kvm);
 }
 
@@ -1846,7 +1846,7 @@  void kvm_apic_post_state_restore(struct kvm_vcpu *vcpu,
 		kvm_x86_ops->hwapic_isr_update(vcpu->kvm,
 				apic_find_highest_isr(apic));
 	kvm_make_request(KVM_REQ_EVENT, vcpu);
-	if (!ioapic_in_kernel(vcpu->kvm))
+	if (ioapic_in_kernel(vcpu->kvm))
 		kvm_rtc_eoi_tracking_restore_one(vcpu);
 }
 
diff --git b/arch/x86/kvm/x86.c a/arch/x86/kvm/x86.c
index 49a98608e3f6..5d2b8695732c 100644
--- b/arch/x86/kvm/x86.c
+++ a/arch/x86/kvm/x86.c
@@ -3573,16 +3573,14 @@  static int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
 		r = -EEXIST;
 		if (irqchip_in_kernel(kvm))
 			goto split_irqchip_unlock;
-		if (!irqchip_split(kvm)) {
-			if (atomic_read(&kvm->online_vcpus))
-				goto split_irqchip_unlock;
-			r = kvm_setup_empty_irq_routing(kvm);
-			if (r)
-				goto split_irqchip_unlock;
-			/* Pairs with irqchip_in_kernel. */
-			smp_wmb();
-			kvm->arch.irqchip_split = true;
-		}
+		if (atomic_read(&kvm->online_vcpus))
+			goto split_irqchip_unlock;
+		r = kvm_setup_empty_irq_routing(kvm);
+		if (r)
+			goto split_irqchip_unlock;
+		/* Pairs with irqchip_in_kernel. */
+		smp_wmb();
+		kvm->arch.irqchip_split = true;
 		r = 0;
 split_irqchip_unlock:
 		mutex_unlock(&kvm->lock);
@@ -3701,7 +3699,7 @@  long kvm_arch_vm_ioctl(struct file *filp,
 		}
 
 		r = -ENXIO;
-		if (!irqchip_in_kernel(kvm) || !ioapic_in_kernel(kvm))
+		if (!irqchip_in_kernel(kvm) || irqchip_split(kvm))
 			goto get_irqchip_out;
 		r = kvm_vm_ioctl_get_irqchip(kvm, chip);
 		if (r)
@@ -3725,7 +3723,7 @@  long kvm_arch_vm_ioctl(struct file *filp,
 		}
 
 		r = -ENXIO;
-		if (!irqchip_in_kernel(kvm) || !ioapic_in_kernel(kvm))
+		if (!irqchip_in_kernel(kvm) || irqchip_split(kvm))
 			goto set_irqchip_out;
 		r = kvm_vm_ioctl_set_irqchip(kvm, chip);
 		if (r)