KVM: arm: Implement software vGICv2 emulation

The emulation code is automatically enabled when one of vGIC resources is missing from the device tree

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

---
 virt/kvm/arm/vgic-v2.c | 29 ++++++++++++++---------------
 virt/kvm/arm/vgic.c    | 10 ++++++----
 2 files changed, 20 insertions(+), 19 deletions(-)

virt/kvm/arm/vgic-v2.c +14 -15

index f9b9c7c..b371a59 100644
@@ -180,22 +180,27 @@ int vgic_v2_probe(struct device_node *vgic_node,
 		  const struct vgic_ops **ops,
 		  const struct vgic_params **params)
 {
-	int ret;
+	int ret = 0;
 	struct resource vctrl_res;
 	struct resource vcpu_res;
 	struct vgic_params *vgic = &vgic_v2_params;
 
+	vgic->nr_lr = VGIC_V2_MAX_LRS;
+
 	vgic->maint_irq = irq_of_parse_and_map(vgic_node, 0);
 	if (!vgic->maint_irq) {
 		kvm_err("error getting vgic maintenance irq from DT\n");
-		ret = -ENXIO;
-		goto out;
+		goto sw_emul;
 	}
 
-	ret = of_address_to_resource(vgic_node, 2, &vctrl_res);
-	if (ret) {
+	if (of_address_to_resource(vgic_node, 2, &vctrl_res)) {
 		kvm_err("Cannot obtain GICH resource\n");
-		goto out;
+		goto sw_emul;
+	}
+
+	if (of_address_to_resource(vgic_node, 3, &vcpu_res)) {
+		kvm_err("Cannot obtain GICV resource\n");
+		goto sw_emul;
 	}
 
 	vgic->vctrl_base = of_iomap(vgic_node, 2);

@@ -216,12 +221,6 @@ int vgic_v2_probe(struct device_node *vgic_node,
 		goto out_unmap;
 	}
 
-	if (of_address_to_resource(vgic_node, 3, &vcpu_res)) {
-		kvm_err("Cannot obtain GICV resource\n");
-		ret = -ENXIO;
-		goto out_unmap;
-	}
-
 	if (!PAGE_ALIGNED(vcpu_res.start)) {
 		kvm_err("GICV physical address 0x%llx not page aligned\n",
 			(unsigned long long)vcpu_res.start);

@@ -237,13 +236,13 @@ int vgic_v2_probe(struct device_node *vgic_node,
 		goto out_unmap;
 	}
 
-	vgic->can_emulate_gicv2 = true;
-	kvm_register_device_ops(&kvm_arm_vgic_v2_ops, KVM_DEV_TYPE_ARM_VGIC_V2);
-
 	vgic->vcpu_base = vcpu_res.start;
 
 	kvm_info("%s@%llx IRQ%d\n", vgic_node->name,
 		 vctrl_res.start, vgic->maint_irq);
+sw_emul:
+	vgic->can_emulate_gicv2 = true;
+	kvm_register_device_ops(&kvm_arm_vgic_v2_ops, KVM_DEV_TYPE_ARM_VGIC_V2);
 
 	vgic->type = VGIC_V2;
 	vgic->max_gic_vcpus = VGIC_V2_MAX_CPUS;

virt/kvm/arm/vgic.c +6 -4

index aec6063..66e0cae 100644
@@ -2196,11 +2196,13 @@ int kvm_vgic_hyp_init(void)
 	if (ret)
 		return ret;
 
-	ret = request_percpu_irq(vgic->maint_irq, vgic_maintenance_handler,
+	if (vgic->maint_irq) {
+		ret = request_percpu_irq(vgic->maint_irq, vgic_maintenance_handler,
 				 "vgic", kvm_get_running_vcpus());
-	if (ret) {
-		kvm_err("Cannot register interrupt %d\n", vgic->maint_irq);
-		return ret;
+		if (ret) {
+			kvm_err("Cannot register interrupt %d\n", vgic->maint_irq);
+			return ret;
+		}
 	}
 
 	ret = __register_cpu_notifier(&vgic_cpu_nb);

Hold on a second. In your cover letter, your saying "RPi-2". The RPi-2 doesn't have a GIC at all, so I'd really like to know *how* you end-up in the GICv2 probe function?

Hello!

Quoted 3 lines

Hold on a second. In your cover letter, your saying "RPi-2". The RPi-2 doesn't have a GIC at all, so I'd really like to know *how* you end-up in the GICv2 probe function?

I'm not on RPi-2. I am on some Samsung's proprietary hardware which suffers from this problem. Actually it has "weird GIC", similar to Exynos-4 (every CPU accesses GIC at its own base), thus hardware vGIC is unusable.

Some hardware (like Raspberry Pi 2) is capable of running KVM, however lacks functional vGIC registers. This series introduces software vGIC emulation for such machines, allowing to fully use virtualization capabilities

Pavel Fedin (3):
KVM: arm: Add basic infrastructure for software vGIC emulation
KVM: arm: Introduce software emulation of vGICv2 CPU interface
KVM: arm: Enable vGICv2 software emulation

 include/kvm/arm_vgic.h      |   4 ++
 virt/kvm/arm/vgic-v2-emul.c |  60 +++++++++++++++--
 virt/kvm/arm/vgic-v2.c      |  29 ++++----
 virt/kvm/arm/vgic.c         | 159 +++++++++++++++++++++++++++++++++-----------
 virt/kvm/arm/vgic.h         |   3 +
 5 files changed, 196 insertions(+), 59 deletions(-)

Some hardware (like Raspberry Pi 2) is capable of running KVM, however lacks functional vGIC registers. This series introduces software vGIC emulation for such machines, allowing to fully use virtualization capabilities

Hi Pavel,

[Please cc the kvm/arm list for such patches according to the MAINTAINERS file in the future]

Quoted 3 lines · Pavel Fedin

Some hardware (like Raspberry Pi 2) is capable of running KVM, however lacks functional vGIC registers. This series introduces software vGIC emulation for such machines, allowing to fully use virtualization capabilities

Is this rather esoteric use case really worth the extra code in the kernel?

I really feel that pure emulation should happen in userspace unless there's a very good reason for doing it in the kernel, such as a clearly measureable difference in performance, etc.

I would much rather see a version of this where a userspace provided GIC works with the in-kernel arch timers support.

-Christoffer

Hi,

Quoted 5 lines · Christoffer Dall

Hi Pavel,

[Please cc the kvm/arm list for such patches according to the MAINTAINERS file in the future]

Quoted 7 lines

Quoted 3 lines · Pavel Fedin

Some hardware (like Raspberry Pi 2) is capable of running KVM, however lacks functional vGIC registers. This series introduces software vGIC emulation for such machines, allowing to fully use virtualization capabilities

Is this rather esoteric use case really worth the extra code in the kernel?

I wonder if these patches would pave the way to support running GICv2 guests on GICv3s without compat support? Admittedly not a really compelling use case either, but at least worth discussing, I think.

Also if this will make the hack needed to enable KVM on RPi2 smaller, I'd rather embrace this one than letting any random hacks appear on that RPi kernel tree (patches which I have seen already on some other repo). If I get this correctly, there are some efforts currently to get closer to mainline with the RPi tree.

Pavel, is this "broken" GIC you are talking about going to appear in a publicly available SoC? If yes, you could either state this right now or send it later once you can talk publicly.

Marc, Christoffer:
So is this GICv2 CPU interface emulation totally out of question for us or is it worth at least commenting on the patches?

Hi,

Quoted 10 lines · Christoffer Dall

Hi Pavel,

[Please cc the kvm/arm list for such patches according to the MAINTAINERS file in the future]

Quoted 3 lines · Pavel Fedin

Some hardware (like Raspberry Pi 2) is capable of running KVM, however lacks functional vGIC registers. This series introduces software vGIC emulation for such machines, allowing to fully use virtualization capabilities

Quoted 2 lines

Is this rather esoteric use case really worth the extra code in the kernel?

I wonder if these patches would pave the way to support running GICv2 guests on GICv3s without compat support? Admittedly not a really compelling use case either, but at least worth discussing, I think.

Also if this will make the hack needed to enable KVM on RPi2 smaller, I'd rather embrace this one than letting any random hacks appear on that RPi kernel tree (patches which I have seen already on some other repo). If I get this correctly, there are some efforts currently to get closer to mainline with the RPi tree.

Pavel, is this "broken" GIC you are talking about going to appear in a publicly available SoC? If yes, you could either state this right now or send it later once you can talk publicly.

Marc, Christoffer:
So is this GICv2 CPU interface emulation totally out of question for us or is it worth at least commenting on the patches?

I wonder if these patches would pave the way to support running GICv2 guests on GICv3s without compat support?

Pavel, is this "broken" GIC you are talking about going to appear in a publicly available SoC?