[RFC PATCH 01/13] KVM: Introduce config option for per-vCPU vLPI enablement

[Maximilian Dittgen <mdittgen@amazon.de>]

Add CONFIG_ARM_GIC_V3_PER_VCPU_VLPI to control whether vLPI direct
injection is to be enabled on a system-wide or a per-vCPU basis.

When enabled, vPEs can be allocated/deallocated to vCPUs on an ad-hoc,
per-vCPU basis in runtime. When disabled, keep current vgic_v4_init
behavior of automatic vCPU vPE allocation upon VM initialization.

We declare three ioctls numbers to manage per-vCPU vLPI enablement:
- KVM_ENABLE_VCPU_VLPI, which given a vCPU ID, allocates a vPE and
initializes the vCPU for receiving direct vLPI interrupts.
- KVM_DISABLE_VCPU_VLPI, which given a vCPU ID, disables the vCPU’s
ability to receive direct vLPI interrupts and frees its underlying vPE
structure.
- KVM_QUERY_VCPU_VLPI, which given a vCPU ID, returns a boolean
describing whether the vCPU is configured to receive direct vLPI
interrupts.

This commit declares the kconfig, ioctl numbers, and documentation.
Implementation will come throughout this patch set.

Signed-off-by: Maximilian Dittgen <mdittgen@amazon.de>
---
 Documentation/virt/kvm/api.rst | 56 ++++++++++++++++++++++++++++++++++
 arch/arm64/kvm/arm.c           | 15 +++++++++
 arch/arm64/kvm/vgic/vgic-v4.c  |  9 ++++++
 arch/arm64/kvm/vgic/vgic.h     |  2 ++
 drivers/irqchip/Kconfig        | 13 ++++++++
 include/uapi/linux/kvm.h       |  6 ++++
 6 files changed, 101 insertions(+)

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index 27f726ff8fe0..dcfb326dff10 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -6517,6 +6517,62 @@ the capability to be present.
 
 `flags` must currently be zero.
 
+4.XXX KVM_ENABLE_VCPU_VLPI
+--------------------------
+
+:Capability: KVM_CAP_ARM_PER_VCPU_VLPI
+:Architectures: arm64
+:Type: vm ioctl
+:Parameters: int vcpu_id (in)
+:Returns: 0 on success, negative value on error
+
+This ioctl enables GICv4 direct vLPI injection for the specified vCPU.
+Allocates vPE structures (doorbell IRQ, vPE table entry, virtual pending
+table, vPEID) and upgrades existing software-forwarded LPIs targeting
+this vCPU to hardware-forwarded vLPIs.
+
+If GICv4.1 is supported and vSGIs are disabled on the specified vCPU,
+this ioctl enables vCPU vSGI support.
+
+Requires CONFIG_ARM_GIC_V3_PER_VCPU_VLPI and GICv4 hardware support.
+
+Returns -EINVAL if vGICv4 is not initialized or if the passed vcpu_id
+does not map to a vCPU.
+
+4.XXX KVM_DISABLE_VCPU_VLPI
+---------------------------
+
+:Capability: KVM_CAP_ARM_PER_VCPU_VLPI
+:Architectures: arm64
+:Type: vm ioctl
+:Parameters: int vcpu_id (in)
+:Returns: 0 on success, negative value on error
+
+This ioctl disables GICv4 direct vLPI injection for the specified vCPU.
+Downgrades hardware-forwarded vLPIs to software-forwarded LPIs and frees
+vPE structures. Pending interrupts in the virtual pending table may be
+lost.
+
+If vSGIs are enabled on the specified vCPU, this ioctl disables them.
+
+Returns -EINVAL if vGICv4 is not initialized or if the passed vcpu_id
+does not map to a vCPU.
+
+4.XXX KVM_QUERY_VCPU_VLPI
+-------------------------
+
+:Capability: KVM_CAP_ARM_PER_VCPU_VLPI
+:Architectures: arm64
+:Type: vm ioctl
+:Parameters: int vcpu_id (in)
+:Returns: 1 if enabled, 0 if disabled, negative value on error
+
+This ioctl queries whether GICv4 direct vLPI injection is enabled for
+the specified vCPU.
+
+Returns -EINVAL if vGICv4 is not initialized or if the passed vcpu_id
+does not map to a vCPU.
+
 
 .. _kvm_run:
 
diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index 452d0c85281e..2839e11ba2c1 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -424,6 +424,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 		else
 			r = kvm_supports_cacheable_pfnmap();
 		break;
+	case KVM_CAP_ARM_PER_VCPU_VLPI:
+		r = kvm_per_vcpu_vlpi_supported();
+		break;
 
 	default:
 		r = 0;
@@ -1947,6 +1950,18 @@ int kvm_arch_vm_ioctl(struct file *filp, unsigned int ioctl, unsigned long arg)
 			return -EFAULT;
 		return kvm_vm_ioctl_get_reg_writable_masks(kvm, &range);
 	}
+	case KVM_ENABLE_VCPU_VLPI: {
+		/* TODO: create ioctl handler function */
+		return -ENOSYS;
+	}
+	case KVM_DISABLE_VCPU_VLPI: {
+		/* TODO: create ioctl handler function */
+		return -ENOSYS;
+	}
+	case KVM_QUERY_VCPU_VLPI: {
+		/* TODO: create ioctl handler function */
+		return -ENOSYS;
+	}
 	default:
 		return -EINVAL;
 	}
diff --git a/arch/arm64/kvm/vgic/vgic-v4.c b/arch/arm64/kvm/vgic/vgic-v4.c
index 09c3e9eb23f8..9ef12c33b3f7 100644
--- a/arch/arm64/kvm/vgic/vgic-v4.c
+++ b/arch/arm64/kvm/vgic/vgic-v4.c
@@ -226,6 +226,15 @@ void vgic_v4_get_vlpi_state(struct vgic_irq *irq, bool *val)
 	*val = !!(*ptr & mask);
 }
 
+bool kvm_per_vcpu_vlpi_supported(void)
+{
+#ifdef CONFIG_ARM_GIC_V3_PER_VCPU_VLPI
+	return kvm_vgic_global_state.has_gicv4;
+#else
+	return false;
+#endif
+}
+
 int vgic_v4_request_vpe_irq(struct kvm_vcpu *vcpu, int irq)
 {
 	return request_irq(irq, vgic_v4_doorbell_handler, 0, "vcpu", vcpu);
diff --git a/arch/arm64/kvm/vgic/vgic.h b/arch/arm64/kvm/vgic/vgic.h
index 5f0fc96b4dc2..99894806a4e9 100644
--- a/arch/arm64/kvm/vgic/vgic.h
+++ b/arch/arm64/kvm/vgic/vgic.h
@@ -467,4 +467,6 @@ static inline bool vgic_is_v3(struct kvm *kvm)
 int vgic_its_debug_init(struct kvm_device *dev);
 void vgic_its_debug_destroy(struct kvm_device *dev);
 
+bool kvm_per_vcpu_vlpi_supported(void);
+
 #endif
diff --git a/drivers/irqchip/Kconfig b/drivers/irqchip/Kconfig
index a61c6dc63c29..1c3e0c6d3177 100644
--- a/drivers/irqchip/Kconfig
+++ b/drivers/irqchip/Kconfig
@@ -52,6 +52,19 @@ config ARM_GIC_V3_ITS
 	default ARM_GIC_V3
 	select IRQ_MSI_IOMMU
 
+config ARM_GIC_V3_PER_VCPU_VLPI
+	bool "ARM GICv4 per-vCPU vLPI direct injection support"
+	depends on ARM_GIC_V3_ITS
+	default n
+	help
+	  Enable GICv4 direct injection of MSIs as vLPIs on a per vCPU
+	  basis. Enables partial vLPI enablement on systems with more
+	  vCPU capacity than vPE capacity. When enabled, all vCPUs
+	  will boot without GICv4 vPE structures and handle interrupts
+	  as software LPIs. KVM_ENABLE_VCPU_VLPI ioctl must then be called on
+	  individual vCPUs to initialize their GICv4 structs and upgrade
+	  targeting LPIs to vLPIs.
+
 config ARM_GIC_V3_ITS_FSL_MC
 	bool
 	depends on ARM_GIC_V3_ITS
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 1e541193e98d..002fe0f4841d 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -973,6 +973,7 @@ struct kvm_enable_cap {
 #define KVM_CAP_ARM_CACHEABLE_PFNMAP_SUPPORTED 243
 #define KVM_CAP_GUEST_MEMFD_FLAGS 244
 #define KVM_CAP_ARM_SEA_TO_USER 245
+#define KVM_CAP_ARM_PER_VCPU_VLPI 246
 
 struct kvm_irq_routing_irqchip {
 	__u32 irqchip;
@@ -1451,6 +1452,11 @@ struct kvm_enc_region {
 #define KVM_GET_SREGS2             _IOR(KVMIO,  0xcc, struct kvm_sregs2)
 #define KVM_SET_SREGS2             _IOW(KVMIO,  0xcd, struct kvm_sregs2)
 
+/* Per-vCPU vLPI enablement/disablement */
+#define KVM_ENABLE_VCPU_VLPI    _IOW(KVMIO, 0xf0, int)
+#define KVM_DISABLE_VCPU_VLPI    _IOW(KVMIO, 0xf1, int)
+#define KVM_QUERY_VCPU_VLPI    _IOR(KVMIO, 0xf2, int)
+
 #define KVM_DIRTY_LOG_MANUAL_PROTECT_ENABLE    (1 << 0)
 #define KVM_DIRTY_LOG_INITIALLY_SET            (1 << 1)
 
-- 
2.50.1 (Apple Git-155)




Amazon Web Services Development Center Germany GmbH
Tamara-Danz-Str. 13
10243 Berlin
Geschaeftsfuehrung: Christian Schlaeger, Christof Hellmis
Eingetragen am Amtsgericht Charlottenburg unter HRB 257764 B
Sitz: Berlin
Ust-ID: DE 365 538 597