Allow to use KVM without in-kernel irqchip

Makes qemu working again with kernel-irqchip=off option

Signed-off-by Pavel Fedin <[email protected]>

---
 virt/kvm/arm/vgic.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

virt/kvm/arm/vgic.c +4 -1

index 78fb820..3420657 100644
@@ -100,6 +100,9 @@ static bool queue_sgi(struct kvm_vcpu *vcpu, int irq)
 
 int kvm_vgic_map_resources(struct kvm *kvm)
 {
+	if (!kvm->arch.vgic.vm_ops.map_resources)
+		return 0;
+
 	return kvm->arch.vgic.vm_ops.map_resources(kvm, vgic);
 }
 

@@ -1637,7 +1640,7 @@ static int vgic_vcpu_init_maps(struct kvm_vcpu *vcpu, int nr_irqs)
  */
 int kvm_vgic_get_max_vcpus(void)
 {
-	return vgic->max_gic_vcpus;
+	return vgic ? vgic->max_gic_vcpus : KVM_MAX_VCPUS;
 }
 
 void kvm_vgic_destroy(struct kvm *kvm)

Signature · 1 line

2.4.4

Allows to use KVM on hardware without vGIC. Interrupt controller has to be emulated in userspace in this case.

Signed-off-by Pavel Fedin <[email protected]>

---
 arch/arm/kvm/arm.c | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

arch/arm/kvm/arm.c +8 -0

index d9631ec..f2f7a13 100644
@@ -61,6 +61,8 @@ static atomic64_t kvm_vmid_gen = ATOMIC64_INIT(1);
 static u8 kvm_next_vmid;
 static DEFINE_SPINLOCK(kvm_vmid_lock);
 
+static bool vgic_present;
+
 static void kvm_arm_set_running_vcpu(struct kvm_vcpu *vcpu)
 {
 	BUG_ON(preemptible());

@@ -172,6 +174,8 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 	switch (ext) {
 	case KVM_CAP_IRQCHIP:
 	case KVM_CAP_IRQFD:
+		r = vgic_present;
+		break;
 	case KVM_CAP_IOEVENTFD:
 	case KVM_CAP_DEVICE_CTRL:
 	case KVM_CAP_USER_MEMORY:

@@ -850,6 +854,8 @@ static int kvm_vm_ioctl_set_device_addr(struct kvm *kvm,
 
 	switch (dev_id) {
 	case KVM_ARM_DEVICE_VGIC_V2:
+		if (!vgic_present)
+			return -ENXIO;
 		return kvm_vgic_addr(kvm, type, &dev_addr->addr, true);
 	default:
 		return -ENODEV;

@@ -864,6 +870,8 @@ long kvm_arch_vm_ioctl(struct file *filp,
 
 	switch (ioctl) {
 	case KVM_CREATE_IRQCHIP: {
+		if (!vgic_present)
+			return -ENXIO;
 		return kvm_vgic_create(kvm, KVM_DEV_TYPE_ARM_VGIC_V2);
 	}
 	case KVM_ARM_SET_DEVICE_ADDR: {

@@ -1046,8 +1054,17 @@ static int init_hyp_mode(void)
 	 * Init HYP view of VGIC

arch/arm/kvm/arm.c +3 -0

+		break;
+	default:
 		goto out_free_context;
+	}
 
 	/*
 	 * Init HYP architected timer support

Signature · 1 line

2.4.4

why not report ENXIO as an error? If probing the vgic fails due to being unable to request the irq or something similar, then surely your system has and error and this should be reported.

This may be more nicely implemented by letting the vgic init/probe functions set the vgic_present, or maybe better yet, just export a function from vgic.c:

bool kvm_vgic_present(void)

{
	return vgic_ops != NULL;
}

Hello!

Quoted 3 lines

why not report ENXIO as an error? If probing the vgic fails due to being unable to request the irq or something similar, then surely your system has and error and this should be reported.

It is reported by probe function itself.
-ENODEV here means there's no GIC at all. -ENXIO happens when, for example, there is GIC node in
the device tree, but it does not specify vGIC resources. Normally this means that vGIC is defunct on the machine.

Quoted 5 lines

This may be more nicely implemented by letting the vgic init/probe functions set the vgic_present, or maybe better yet, just export a function from vgic.c:

Quoted 4 lines

bool kvm_vgic_present(void)

{
	return vgic_ops != NULL;
}

Is it necessary? Actually this flag is not needed anywhere else except arch/arm/kvm/arm.c, only at
init time. Runtime should, i believe, use irqchip_in_kernel(), because userland can choose just not to use vGIC for some reason (testing for example).

I'd like to distinguish between the 'missing vgic' and 'something bad happened when trying to initialize the vgic' cases, which I don't think we do currently, because the ENXIO code is used in various situations.

I feel the init flow is relatively difficult to follow and adding a bunch of flags here and there doesn't seem to help. By adding a function with a proper comment, it should be more clear, and I don't like the switch statement on the error return values.

-----Original Message-----
From: Christoffer Dall [mailto:[email protected]]
Sent: Thursday, July 09, 2015 4:25 PM
To: Pavel Fedin
Cc: [email protected]; [email protected]; 'Marc Zyngier'
Subject: Re: [PATCH 2/2] Detect vGIC presence at runtime

Quoted 8 lines · Pavel Fedin

Hello!

Quoted 3 lines

why not report ENXIO as an error? If probing the vgic fails due to being unable to request the irq or something similar, then surely your system has and error and this should be reported.

It is reported by probe function itself.
-ENODEV here means there's no GIC at all. -ENXIO happens when, for example, there is GIC node

Quoted 1 line

the device tree, but it does not specify vGIC resources. Normally this means that vGIC is

Quoted 7 lines

the machine.

Quoted 4 lines

This may be more nicely implemented by letting the vgic init/probe functions set the vgic_present, or maybe better yet, just export a function from vgic.c:

Quoted 6 lines

Quoted 4 lines

bool kvm_vgic_present(void)

{
	return vgic_ops != NULL;
}

Is it necessary? Actually this flag is not needed anywhere else except arch/arm/kvm/arm.c, only

Quoted 1 line

init time. Runtime should, i believe, use irqchip_in_kernel(), because userland can choose just

Quoted 2 lines

to use vGIC for some reason (testing for example).

I feel the init flow is relatively difficult to follow and adding a bunch of flags here and there doesn't seem to help. By adding a function with a proper comment, it should be more clear, and I don't like the switch statement on the error return values.

-Christoffer