[PATCH v2 0/4] KVM: arm64: Add attribute to control GICD_TYPER2.nASSGIcap

[PATCH v2 0/4] KVM: arm64: Add attribute to control GICD_TYPER2.nASSGIcap

[Oliver Upton]

Raghu, I applied this locally for review and wound up changing enough
things to where it was easier just to repost. Sorry, hope you don't
mind.

v1: https://lore.kernel.org/kvmarm/20250514192159.1751538-1-rananta@google.com/

v1 -> v2:
 - Drop all use of GICv4 in the UAPI and KVM-internal helpers in favor
   of nASSGIcap. This changes things around to model a guest feature,
   not a host feature.

 - Consolidate UAPI into a single attribute and expect userspace to use
   to read the attribute for discovery, much like we do with the ID
   registers

 - Squash documentation together with implementation

 - Clean up maintenance IRQ attribute handling, which I ran into as part
   of reviewing this series

Oliver Upton (2):
  KVM: arm64: Disambiguate support for vSGIs v. vLPIs
  KVM: arm64: vgic-v3: Consolidate MAINT_IRQ handling

Raghavendra Rao Ananta (2):
  KVM: arm64: Introduce attribute to control GICD_TYPER2.nASSGIcap
  KVM: arm64: selftests: Add test for nASSGIcap attribute

 .../virt/kvm/devices/arm-vgic-v3.rst          | 29 ++++++
 arch/arm64/include/uapi/asm/kvm.h             |  3 +
 arch/arm64/kvm/vgic/vgic-init.c               |  7 +-
 arch/arm64/kvm/vgic/vgic-kvm-device.c         | 88 +++++++++++++------
 arch/arm64/kvm/vgic/vgic-mmio-v3.c            | 24 +++--
 arch/arm64/kvm/vgic/vgic-v4.c                 |  4 +-
 arch/arm64/kvm/vgic/vgic.c                    |  4 +-
 arch/arm64/kvm/vgic/vgic.h                    |  7 ++
 include/kvm/arm_vgic.h                        |  3 +
 tools/testing/selftests/kvm/arm64/vgic_init.c | 41 +++++++++
 10 files changed, 172 insertions(+), 38 deletions(-)


base-commit: 1b85d923ba8c9e6afaf19e26708411adde94fba8
-- 
2.39.5

[PATCH v2 1/4] KVM: arm64: Disambiguate support for vSGIs v. vLPIs

[Oliver Upton]

vgic_supports_direct_msis() is a bit of a misnomer, as it returns true
if either vSGIs or vLPIs are supported. Pick it apart into a few
predicates and replace some open-coded checks for vSGIs.

Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
---
 arch/arm64/kvm/vgic/vgic-init.c    |  4 ++--
 arch/arm64/kvm/vgic/vgic-mmio-v3.c | 16 ++++++++++------
 arch/arm64/kvm/vgic/vgic-v4.c      |  4 ++--
 arch/arm64/kvm/vgic/vgic.c         |  4 ++--
 arch/arm64/kvm/vgic/vgic.h         |  7 +++++++
 5 files changed, 23 insertions(+), 12 deletions(-)

diff --git a/arch/arm64/kvm/vgic/vgic-init.c b/arch/arm64/kvm/vgic/vgic-init.c
index 1f33e71c2a73..fd9e639cd665 100644
--- a/arch/arm64/kvm/vgic/vgic-init.c
+++ b/arch/arm64/kvm/vgic/vgic-init.c
@@ -370,7 +370,7 @@ int vgic_init(struct kvm *kvm)
 	 * v4 support so that we get HW-accelerated vSGIs. Otherwise, only
 	 * enable it if we present a virtual ITS to the guest.
 	 */
-	if (vgic_supports_direct_msis(kvm)) {
+	if (vgic_supports_direct_irqs(kvm)) {
 		ret = vgic_v4_init(kvm);
 		if (ret)
 			goto out;
@@ -418,7 +418,7 @@ static void kvm_vgic_dist_destroy(struct kvm *kvm)
 		dist->vgic_cpu_base = VGIC_ADDR_UNDEF;
 	}
 
-	if (vgic_supports_direct_msis(kvm))
+	if (vgic_supports_direct_irqs(kvm))
 		vgic_v4_teardown(kvm);
 
 	xa_destroy(&dist->lpi_xa);
diff --git a/arch/arm64/kvm/vgic/vgic-mmio-v3.c b/arch/arm64/kvm/vgic/vgic-mmio-v3.c
index ae4c0593d114..1a9c5b4418b2 100644
--- a/arch/arm64/kvm/vgic/vgic-mmio-v3.c
+++ b/arch/arm64/kvm/vgic/vgic-mmio-v3.c
@@ -50,8 +50,12 @@ bool vgic_has_its(struct kvm *kvm)
 
 bool vgic_supports_direct_msis(struct kvm *kvm)
 {
-	return (kvm_vgic_global_state.has_gicv4_1 ||
-		(kvm_vgic_global_state.has_gicv4 && vgic_has_its(kvm)));
+	return kvm_vgic_global_state.has_gicv4 && vgic_has_its(kvm);
+}
+
+bool vgic_supports_direct_sgis(struct kvm *kvm)
+{
+	return kvm_vgic_global_state.has_gicv4_1 && gic_cpuif_has_vsgi();
 }
 
 /*
@@ -86,7 +90,7 @@ static unsigned long vgic_mmio_read_v3_misc(struct kvm_vcpu *vcpu,
 		}
 		break;
 	case GICD_TYPER2:
-		if (kvm_vgic_global_state.has_gicv4_1 && gic_cpuif_has_vsgi())
+		if (vgic_supports_direct_sgis(vcpu->kvm))
 			value = GICD_TYPER2_nASSGIcap;
 		break;
 	case GICD_IIDR:
@@ -119,7 +123,7 @@ static void vgic_mmio_write_v3_misc(struct kvm_vcpu *vcpu,
 		dist->enabled = val & GICD_CTLR_ENABLE_SS_G1;
 
 		/* Not a GICv4.1? No HW SGIs */
-		if (!kvm_vgic_global_state.has_gicv4_1 || !gic_cpuif_has_vsgi())
+		if (!vgic_supports_direct_sgis(vcpu->kvm))
 			val &= ~GICD_CTLR_nASSGIreq;
 
 		/* Dist stays enabled? nASSGIreq is RO */
@@ -133,7 +137,7 @@ static void vgic_mmio_write_v3_misc(struct kvm_vcpu *vcpu,
 		if (is_hwsgi != dist->nassgireq)
 			vgic_v4_configure_vsgis(vcpu->kvm);
 
-		if (kvm_vgic_global_state.has_gicv4_1 &&
+		if (vgic_supports_direct_sgis(vcpu->kvm) &&
 		    was_enabled != dist->enabled)
 			kvm_make_all_cpus_request(vcpu->kvm, KVM_REQ_RELOAD_GICv4);
 		else if (!was_enabled && dist->enabled)
@@ -178,7 +182,7 @@ static int vgic_mmio_uaccess_write_v3_misc(struct kvm_vcpu *vcpu,
 		}
 	case GICD_CTLR:
 		/* Not a GICv4.1? No HW SGIs */
-		if (!kvm_vgic_global_state.has_gicv4_1)
+		if (vgic_supports_direct_sgis(vcpu->kvm))
 			val &= ~GICD_CTLR_nASSGIreq;
 
 		dist->enabled = val & GICD_CTLR_ENABLE_SS_G1;
diff --git a/arch/arm64/kvm/vgic/vgic-v4.c b/arch/arm64/kvm/vgic/vgic-v4.c
index c7de6154627c..a9c772697a43 100644
--- a/arch/arm64/kvm/vgic/vgic-v4.c
+++ b/arch/arm64/kvm/vgic/vgic-v4.c
@@ -356,7 +356,7 @@ int vgic_v4_put(struct kvm_vcpu *vcpu)
 {
 	struct its_vpe *vpe = &vcpu->arch.vgic_cpu.vgic_v3.its_vpe;
 
-	if (!vgic_supports_direct_msis(vcpu->kvm) || !vpe->resident)
+	if (!vgic_supports_direct_irqs(vcpu->kvm) || !vpe->resident)
 		return 0;
 
 	return its_make_vpe_non_resident(vpe, vgic_v4_want_doorbell(vcpu));
@@ -367,7 +367,7 @@ int vgic_v4_load(struct kvm_vcpu *vcpu)
 	struct its_vpe *vpe = &vcpu->arch.vgic_cpu.vgic_v3.its_vpe;
 	int err;
 
-	if (!vgic_supports_direct_msis(vcpu->kvm) || vpe->resident)
+	if (!vgic_supports_direct_irqs(vcpu->kvm) || vpe->resident)
 		return 0;
 
 	if (vcpu_get_flag(vcpu, IN_WFI))
diff --git a/arch/arm64/kvm/vgic/vgic.c b/arch/arm64/kvm/vgic/vgic.c
index 8f8096d48925..f5148b38120a 100644
--- a/arch/arm64/kvm/vgic/vgic.c
+++ b/arch/arm64/kvm/vgic/vgic.c
@@ -951,7 +951,7 @@ void kvm_vgic_flush_hwstate(struct kvm_vcpu *vcpu)
 	 * can be directly injected (GICv4).
 	 */
 	if (list_empty(&vcpu->arch.vgic_cpu.ap_list_head) &&
-	    !vgic_supports_direct_msis(vcpu->kvm))
+	    !vgic_supports_direct_irqs(vcpu->kvm))
 		return;
 
 	DEBUG_SPINLOCK_BUG_ON(!irqs_disabled());
@@ -965,7 +965,7 @@ void kvm_vgic_flush_hwstate(struct kvm_vcpu *vcpu)
 	if (can_access_vgic_from_kernel())
 		vgic_restore_state(vcpu);
 
-	if (vgic_supports_direct_msis(vcpu->kvm))
+	if (vgic_supports_direct_irqs(vcpu->kvm))
 		vgic_v4_commit(vcpu);
 }
 
diff --git a/arch/arm64/kvm/vgic/vgic.h b/arch/arm64/kvm/vgic/vgic.h
index 4349084cb9a6..ebf9ed6adeac 100644
--- a/arch/arm64/kvm/vgic/vgic.h
+++ b/arch/arm64/kvm/vgic/vgic.h
@@ -370,6 +370,13 @@ int vgic_its_inv_lpi(struct kvm *kvm, struct vgic_irq *irq);
 int vgic_its_invall(struct kvm_vcpu *vcpu);
 
 bool vgic_supports_direct_msis(struct kvm *kvm);
+bool vgic_supports_direct_sgis(struct kvm *kvm);
+
+static inline bool vgic_supports_direct_irqs(struct kvm *kvm)
+{
+	return vgic_supports_direct_msis(kvm) || vgic_supports_direct_sgis(kvm);
+}
+
 int vgic_v4_init(struct kvm *kvm);
 void vgic_v4_teardown(struct kvm *kvm);
 void vgic_v4_configure_vsgis(struct kvm *kvm);
-- 
2.39.5

[PATCH v2 2/4] KVM: arm64: vgic-v3: Consolidate MAINT_IRQ handling

[Oliver Upton]

Consolidate the duplicated handling of the VGICv3 maintenance IRQ
attribute as a regular GICv3 attribute, as it is neither a register nor
a common attribute.

Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
---
 arch/arm64/kvm/vgic/vgic-kvm-device.c | 51 +++++++++++++--------------
 1 file changed, 25 insertions(+), 26 deletions(-)

diff --git a/arch/arm64/kvm/vgic/vgic-kvm-device.c b/arch/arm64/kvm/vgic/vgic-kvm-device.c
index 359094f68c23..b0baad68777c 100644
--- a/arch/arm64/kvm/vgic/vgic-kvm-device.c
+++ b/arch/arm64/kvm/vgic/vgic-kvm-device.c
@@ -303,12 +303,6 @@ static int vgic_get_common_attr(struct kvm_device *dev,
 			     VGIC_NR_PRIVATE_IRQS, uaddr);
 		break;
 	}
-	case KVM_DEV_ARM_VGIC_GRP_MAINT_IRQ: {
-		u32 __user *uaddr = (u32 __user *)(long)attr->addr;
-
-		r = put_user(dev->kvm->arch.vgic.mi_intid, uaddr);
-		break;
-	}
 	}
 
 	return r;
@@ -523,7 +517,7 @@ static int vgic_v3_attr_regs_access(struct kvm_device *dev,
 	struct vgic_reg_attr reg_attr;
 	gpa_t addr;
 	struct kvm_vcpu *vcpu;
-	bool uaccess, post_init = true;
+	bool uaccess;
 	u32 val;
 	int ret;
 
@@ -539,9 +533,6 @@ static int vgic_v3_attr_regs_access(struct kvm_device *dev,
 		/* Sysregs uaccess is performed by the sysreg handling code */
 		uaccess = false;
 		break;
-	case KVM_DEV_ARM_VGIC_GRP_MAINT_IRQ:
-		post_init = false;
-		fallthrough;
 	default:
 		uaccess = true;
 	}
@@ -561,7 +552,7 @@ static int vgic_v3_attr_regs_access(struct kvm_device *dev,
 
 	mutex_lock(&dev->kvm->arch.config_lock);
 
-	if (post_init != vgic_initialized(dev->kvm)) {
+	if (!vgic_initialized(dev->kvm)) {
 		ret = -EBUSY;
 		goto out;
 	}
@@ -591,19 +582,6 @@ static int vgic_v3_attr_regs_access(struct kvm_device *dev,
 		}
 		break;
 	}
-	case KVM_DEV_ARM_VGIC_GRP_MAINT_IRQ:
-		if (!is_write) {
-			val = dev->kvm->arch.vgic.mi_intid;
-			ret = 0;
-			break;
-		}
-
-		ret = -EINVAL;
-		if ((val < VGIC_NR_PRIVATE_IRQS) && (val >= VGIC_NR_SGIS)) {
-			dev->kvm->arch.vgic.mi_intid = val;
-			ret = 0;
-		}
-		break;
 	default:
 		ret = -EINVAL;
 		break;
@@ -630,8 +608,24 @@ static int vgic_v3_set_attr(struct kvm_device *dev,
 	case KVM_DEV_ARM_VGIC_GRP_REDIST_REGS:
 	case KVM_DEV_ARM_VGIC_GRP_CPU_SYSREGS:
 	case KVM_DEV_ARM_VGIC_GRP_LEVEL_INFO:
-	case KVM_DEV_ARM_VGIC_GRP_MAINT_IRQ:
 		return vgic_v3_attr_regs_access(dev, attr, true);
+	case KVM_DEV_ARM_VGIC_GRP_MAINT_IRQ: {
+		u32 __user *uaddr = (u32 __user *)attr->addr;
+		u32 val;
+
+		if (get_user(val, uaddr))
+			return -EFAULT;
+
+		guard(mutex)(&dev->kvm->arch.config_lock);
+		if (vgic_initialized(dev->kvm))
+			return -EBUSY;
+
+		if ((val < VGIC_NR_SGIS) || (val >= VGIC_NR_PRIVATE_IRQS))
+			return -EINVAL;
+
+		dev->kvm->arch.vgic.mi_intid = val;
+		return 0;
+	}
 	default:
 		return vgic_set_common_attr(dev, attr);
 	}
@@ -645,8 +639,13 @@ static int vgic_v3_get_attr(struct kvm_device *dev,
 	case KVM_DEV_ARM_VGIC_GRP_REDIST_REGS:
 	case KVM_DEV_ARM_VGIC_GRP_CPU_SYSREGS:
 	case KVM_DEV_ARM_VGIC_GRP_LEVEL_INFO:
-	case KVM_DEV_ARM_VGIC_GRP_MAINT_IRQ:
 		return vgic_v3_attr_regs_access(dev, attr, false);
+	case KVM_DEV_ARM_VGIC_GRP_MAINT_IRQ: {
+		u32 __user *uaddr = (u32 __user *)(long)attr->addr;
+
+		guard(mutex)(&dev->kvm->arch.config_lock);
+		return put_user(dev->kvm->arch.vgic.mi_intid, uaddr);
+	}
 	default:
 		return vgic_get_common_attr(dev, attr);
 	}
-- 
2.39.5

[PATCH v2 3/4] KVM: arm64: Introduce attribute to control GICD_TYPER2.nASSGIcap

[Oliver Upton]

From: Raghavendra Rao Ananta <rananta@google.com>

KVM unconditionally advertises GICD_TYPER2.nASSGIcap (which internally
implies vSGIs) on GICv4.1 systems. Allow userspace to change whether a
VM supports the feature. Only allow changes prior to VGIC initialization
as at that point vPEs need to be allocated for the VM.

For convenience, bundle support for vLPIs and vSGIs behind this feature,
allowing userspace to control vPE allocation for VMs in environments
that may be constrained on vPE IDs.

Signed-off-by: Raghavendra Rao Ananta <rananta@google.com>
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
---
 .../virt/kvm/devices/arm-vgic-v3.rst          | 29 +++++++++++++++
 arch/arm64/include/uapi/asm/kvm.h             |  3 ++
 arch/arm64/kvm/vgic/vgic-init.c               |  3 ++
 arch/arm64/kvm/vgic/vgic-kvm-device.c         | 37 +++++++++++++++++++
 arch/arm64/kvm/vgic/vgic-mmio-v3.c            | 10 ++++-
 include/kvm/arm_vgic.h                        |  3 ++
 6 files changed, 84 insertions(+), 1 deletion(-)

diff --git a/Documentation/virt/kvm/devices/arm-vgic-v3.rst b/Documentation/virt/kvm/devices/arm-vgic-v3.rst
index e860498b1e35..049d77eae591 100644
--- a/Documentation/virt/kvm/devices/arm-vgic-v3.rst
+++ b/Documentation/virt/kvm/devices/arm-vgic-v3.rst
@@ -306,3 +306,32 @@ Groups:
 
     The vINTID specifies which interrupt is generated when the vGIC
     must generate a maintenance interrupt. This must be a PPI.
+
+  KVM_DEV_ARM_VGIC_GRP_FEATURES
+   Attributes:
+
+    KVM_DEV_ARM_VGIC_FEATURE_nASSGIcap
+      Control whether support for SGIs without an active state is exposed
+      to the VM. attr->addr points to a __u8 value which indicates whether
+      he feature is enabled / disabled.
+
+      A value of 0 indicates that the feature is disabled. A nonzero value
+      indicates that the feature is enabled.
+
+      This attribute can only be set prior to initializing the VGIC (i.e.
+      KVM_DEV_ARM_VGIC_CTRL_INIT).
+
+      Support for SGIs without an active state depends on hardware support.
+      Userspace can discover support for the feature by reading the
+      attribute after creating a VGICv3. It is possible that
+      KVM_DEV_ARM_VGIC_CTRL_INIT can later fail if this feature is enabled
+      and KVM is unable to allocate GIC vPEs for the VM.
+
+  Errors:
+
+    =======  ========================================================
+    -ENXIO   Invalid attribute in attr->attr
+    -EFAULT  Invalid user address in attr->addr
+    -EBUSY   The VGIC has already been initialized
+    -EINVAL  KVM doesn't support the requested feature setting
+    =======  ========================================================
diff --git a/arch/arm64/include/uapi/asm/kvm.h b/arch/arm64/include/uapi/asm/kvm.h
index ed5f3892674c..41e9ce412afd 100644
--- a/arch/arm64/include/uapi/asm/kvm.h
+++ b/arch/arm64/include/uapi/asm/kvm.h
@@ -417,6 +417,7 @@ enum {
 #define KVM_DEV_ARM_VGIC_GRP_LEVEL_INFO  7
 #define KVM_DEV_ARM_VGIC_GRP_ITS_REGS 8
 #define KVM_DEV_ARM_VGIC_GRP_MAINT_IRQ  9
+#define KVM_DEV_ARM_VGIC_GRP_FEATURES 10
 #define KVM_DEV_ARM_VGIC_LINE_LEVEL_INFO_SHIFT	10
 #define KVM_DEV_ARM_VGIC_LINE_LEVEL_INFO_MASK \
 			(0x3fffffULL << KVM_DEV_ARM_VGIC_LINE_LEVEL_INFO_SHIFT)
@@ -429,6 +430,8 @@ enum {
 #define   KVM_DEV_ARM_VGIC_SAVE_PENDING_TABLES	3
 #define   KVM_DEV_ARM_ITS_CTRL_RESET		4
 
+#define   KVM_DEV_ARM_VGIC_FEATURE_nASSGIcap	0
+
 /* Device Control API on vcpu fd */
 #define KVM_ARM_VCPU_PMU_V3_CTRL	0
 #define   KVM_ARM_VCPU_PMU_V3_IRQ		0
diff --git a/arch/arm64/kvm/vgic/vgic-init.c b/arch/arm64/kvm/vgic/vgic-init.c
index fd9e639cd665..93a616131ed6 100644
--- a/arch/arm64/kvm/vgic/vgic-init.c
+++ b/arch/arm64/kvm/vgic/vgic-init.c
@@ -132,6 +132,9 @@ int kvm_vgic_create(struct kvm *kvm, u32 type)
 
 	kvm->arch.vgic.in_kernel = true;
 	kvm->arch.vgic.vgic_model = type;
+	if (type == KVM_DEV_TYPE_ARM_VGIC_V3)
+		kvm->arch.vgic.nassgicap = kvm_vgic_global_state.has_gicv4_1 &&
+					   gic_cpuif_has_vsgi();
 
 	kvm->arch.vgic.vgic_dist_base = VGIC_ADDR_UNDEF;
 
diff --git a/arch/arm64/kvm/vgic/vgic-kvm-device.c b/arch/arm64/kvm/vgic/vgic-kvm-device.c
index b0baad68777c..c9d41ae9fe4f 100644
--- a/arch/arm64/kvm/vgic/vgic-kvm-device.c
+++ b/arch/arm64/kvm/vgic/vgic-kvm-device.c
@@ -626,6 +626,26 @@ static int vgic_v3_set_attr(struct kvm_device *dev,
 		dev->kvm->arch.vgic.mi_intid = val;
 		return 0;
 	}
+	case KVM_DEV_ARM_VGIC_GRP_FEATURES: {
+		u8 __user *uaddr = (u8 __user *)attr->addr;
+		u8 val;
+
+		if (attr->attr != KVM_DEV_ARM_VGIC_FEATURE_nASSGIcap)
+			return -ENXIO;
+
+		if (get_user(val, uaddr))
+			return -EFAULT;
+
+		guard(mutex)(&dev->kvm->arch.config_lock);
+		if (vgic_initialized(dev->kvm))
+			return -EBUSY;
+
+		if (!(kvm_vgic_global_state.has_gicv4_1 && gic_cpuif_has_vsgi()) && val)
+			return -EINVAL;
+
+		dev->kvm->arch.vgic.nassgicap = val;
+		return 0;
+	}
 	default:
 		return vgic_set_common_attr(dev, attr);
 	}
@@ -646,6 +666,17 @@ static int vgic_v3_get_attr(struct kvm_device *dev,
 		guard(mutex)(&dev->kvm->arch.config_lock);
 		return put_user(dev->kvm->arch.vgic.mi_intid, uaddr);
 	}
+	case KVM_DEV_ARM_VGIC_GRP_FEATURES: {
+		u8 __user *uaddr = (u8 __user *)attr->addr;
+		u8 val;
+
+		if (attr->attr != KVM_DEV_ARM_VGIC_FEATURE_nASSGIcap)
+			return -ENXIO;
+
+		guard(mutex)(&dev->kvm->arch.config_lock);
+		val = dev->kvm->arch.vgic.nassgicap;
+		return put_user(val, uaddr);
+	}
 	default:
 		return vgic_get_common_attr(dev, attr);
 	}
@@ -683,8 +714,14 @@ static int vgic_v3_has_attr(struct kvm_device *dev,
 			return 0;
 		case KVM_DEV_ARM_VGIC_SAVE_PENDING_TABLES:
 			return 0;
+		default:
+			return -ENXIO;
 		}
+	case KVM_DEV_ARM_VGIC_GRP_FEATURES:
+		return attr->attr != KVM_DEV_ARM_VGIC_FEATURE_nASSGIcap ?
+		       -ENXIO : 0;
 	}
+
 	return -ENXIO;
 }
 
diff --git a/arch/arm64/kvm/vgic/vgic-mmio-v3.c b/arch/arm64/kvm/vgic/vgic-mmio-v3.c
index 1a9c5b4418b2..43f59e70e1a2 100644
--- a/arch/arm64/kvm/vgic/vgic-mmio-v3.c
+++ b/arch/arm64/kvm/vgic/vgic-mmio-v3.c
@@ -50,12 +50,20 @@ bool vgic_has_its(struct kvm *kvm)
 
 bool vgic_supports_direct_msis(struct kvm *kvm)
 {
+	/*
+	 * Deliberately conflate vLPI and vSGI support on GICv4.1 hardware,
+	 * indirectly allowing userspace to control whether or not vPEs are
+	 * allocated for the VM.
+	 */
+	if (kvm_vgic_global_state.has_gicv4_1 && !vgic_supports_direct_sgis(kvm))
+		return false;
+
 	return kvm_vgic_global_state.has_gicv4 && vgic_has_its(kvm);
 }
 
 bool vgic_supports_direct_sgis(struct kvm *kvm)
 {
-	return kvm_vgic_global_state.has_gicv4_1 && gic_cpuif_has_vsgi();
+	return kvm->arch.vgic.nassgicap;
 }
 
 /*
diff --git a/include/kvm/arm_vgic.h b/include/kvm/arm_vgic.h
index 714cef854c1c..0e8cface0878 100644
--- a/include/kvm/arm_vgic.h
+++ b/include/kvm/arm_vgic.h
@@ -264,6 +264,9 @@ struct vgic_dist {
 	/* distributor enabled */
 	bool			enabled;
 
+	/* Supports SGIs without active state */
+	bool			nassgicap;
+
 	/* Wants SGIs without active state */
 	bool			nassgireq;
 
-- 
2.39.5

Re: [PATCH v2 3/4] KVM: arm64: Introduce attribute to control GICD_TYPER2.nASSGIcap

[Raghavendra Rao Ananta]

Hi Oliver,

On Fri, May 30, 2025 at 6:26 PM Oliver Upton <oliver.upton@linux.dev> wrote:
>
> From: Raghavendra Rao Ananta <rananta@google.com>
>
> KVM unconditionally advertises GICD_TYPER2.nASSGIcap (which internally
> implies vSGIs) on GICv4.1 systems. Allow userspace to change whether a
> VM supports the feature. Only allow changes prior to VGIC initialization
> as at that point vPEs need to be allocated for the VM.
>
> For convenience, bundle support for vLPIs and vSGIs behind this feature,
> allowing userspace to control vPE allocation for VMs in environments
> that may be constrained on vPE IDs.
>
> Signed-off-by: Raghavendra Rao Ananta <rananta@google.com>
> Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
> ---
>  .../virt/kvm/devices/arm-vgic-v3.rst          | 29 +++++++++++++++
>  arch/arm64/include/uapi/asm/kvm.h             |  3 ++
>  arch/arm64/kvm/vgic/vgic-init.c               |  3 ++
>  arch/arm64/kvm/vgic/vgic-kvm-device.c         | 37 +++++++++++++++++++
>  arch/arm64/kvm/vgic/vgic-mmio-v3.c            | 10 ++++-
>  include/kvm/arm_vgic.h                        |  3 ++
>  6 files changed, 84 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/virt/kvm/devices/arm-vgic-v3.rst b/Documentation/virt/kvm/devices/arm-vgic-v3.rst
> index e860498b1e35..049d77eae591 100644
> --- a/Documentation/virt/kvm/devices/arm-vgic-v3.rst
> +++ b/Documentation/virt/kvm/devices/arm-vgic-v3.rst
> @@ -306,3 +306,32 @@ Groups:
>
>      The vINTID specifies which interrupt is generated when the vGIC
>      must generate a maintenance interrupt. This must be a PPI.
> +
> +  KVM_DEV_ARM_VGIC_GRP_FEATURES
> +   Attributes:
> +
> +    KVM_DEV_ARM_VGIC_FEATURE_nASSGIcap
> +      Control whether support for SGIs without an active state is exposed
> +      to the VM. attr->addr points to a __u8 value which indicates whether
> +      he feature is enabled / disabled.
> +
nit: s/he/the

> diff --git a/arch/arm64/kvm/vgic/vgic-kvm-device.c b/arch/arm64/kvm/vgic/vgic-kvm-device.c
> index b0baad68777c..c9d41ae9fe4f 100644
> --- a/arch/arm64/kvm/vgic/vgic-kvm-device.c
> +++ b/arch/arm64/kvm/vgic/vgic-kvm-device.c
> @@ -626,6 +626,26 @@ static int vgic_v3_set_attr(struct kvm_device *dev,
>                 dev->kvm->arch.vgic.mi_intid = val;
>                 return 0;
>         }
> +       case KVM_DEV_ARM_VGIC_GRP_FEATURES: {
> +               u8 __user *uaddr = (u8 __user *)attr->addr;
> +               u8 val;
> +
> +               if (attr->attr != KVM_DEV_ARM_VGIC_FEATURE_nASSGIcap)
> +                       return -ENXIO;
> +
> +               if (get_user(val, uaddr))
> +                       return -EFAULT;
> +
> +               guard(mutex)(&dev->kvm->arch.config_lock);
> +               if (vgic_initialized(dev->kvm))
> +                       return -EBUSY;
> +
Do we want to return success if userspace isn't trying to change the
value (similar to sysreg/fw-reg writes)?

> +               if (!(kvm_vgic_global_state.has_gicv4_1 && gic_cpuif_has_vsgi()) && val)
> +                       return -EINVAL;
> +
> +               dev->kvm->arch.vgic.nassgicap = val;
> +               return 0;
> +       }
>         default:
>                 return vgic_set_common_attr(dev, attr);
>         }
> diff --git a/arch/arm64/kvm/vgic/vgic-mmio-v3.c b/arch/arm64/kvm/vgic/vgic-mmio-v3.c
> index 1a9c5b4418b2..43f59e70e1a2 100644
> --- a/arch/arm64/kvm/vgic/vgic-mmio-v3.c
> +++ b/arch/arm64/kvm/vgic/vgic-mmio-v3.c
> @@ -50,12 +50,20 @@ bool vgic_has_its(struct kvm *kvm)
>
>  bool vgic_supports_direct_msis(struct kvm *kvm)
>  {
> +       /*
> +        * Deliberately conflate vLPI and vSGI support on GICv4.1 hardware,
> +        * indirectly allowing userspace to control whether or not vPEs are
> +        * allocated for the VM.
> +        */
> +       if (kvm_vgic_global_state.has_gicv4_1 && !vgic_supports_direct_sgis(kvm))
> +               return false;
> +
Since vgic_supports_direct_sgis() is derived from
'kvm_vgic_global_state.has_gicv4_1', do we still need to depend on the
latter?

Also just to double-check, there are other references that directly
read 'kvm_vgic_global_state.has_gicv4_1' (vgic_v3_map_resources() for
instance). Do we not want them to be replaced with
vgic_supports_direct_sgis()?

Thank you.
Raghavendra

Re: [PATCH v2 3/4] KVM: arm64: Introduce attribute to control GICD_TYPER2.nASSGIcap

[Oliver Upton]

On Tue, Jun 03, 2025 at 11:33:08AM -0700, Raghavendra Rao Ananta wrote:
> > diff --git a/arch/arm64/kvm/vgic/vgic-kvm-device.c b/arch/arm64/kvm/vgic/vgic-kvm-device.c
> > index b0baad68777c..c9d41ae9fe4f 100644
> > --- a/arch/arm64/kvm/vgic/vgic-kvm-device.c
> > +++ b/arch/arm64/kvm/vgic/vgic-kvm-device.c
> > @@ -626,6 +626,26 @@ static int vgic_v3_set_attr(struct kvm_device *dev,
> >                 dev->kvm->arch.vgic.mi_intid = val;
> >                 return 0;
> >         }
> > +       case KVM_DEV_ARM_VGIC_GRP_FEATURES: {
> > +               u8 __user *uaddr = (u8 __user *)attr->addr;
> > +               u8 val;
> > +
> > +               if (attr->attr != KVM_DEV_ARM_VGIC_FEATURE_nASSGIcap)
> > +                       return -ENXIO;
> > +
> > +               if (get_user(val, uaddr))
> > +                       return -EFAULT;
> > +
> > +               guard(mutex)(&dev->kvm->arch.config_lock);
> > +               if (vgic_initialized(dev->kvm))
> > +                       return -EBUSY;
> > +
> Do we want to return success if userspace isn't trying to change the
> value (similar to sysreg/fw-reg writes)?

I'd rather not. Things that are accessible through KVM_*_ONE_REG get
special treatment since VMMs blindly save/restore the entire list of
system registers. The general expectation there is that the VMM and
always write back what it has read.

Since this is an entirely new UAPI I want to impose as much limitation
as possible on userspace :)

> >  bool vgic_supports_direct_msis(struct kvm *kvm)
> >  {
> > +       /*
> > +        * Deliberately conflate vLPI and vSGI support on GICv4.1 hardware,
> > +        * indirectly allowing userspace to control whether or not vPEs are
> > +        * allocated for the VM.
> > +        */
> > +       if (kvm_vgic_global_state.has_gicv4_1 && !vgic_supports_direct_sgis(kvm))
> > +               return false;
> > +
> Since vgic_supports_direct_sgis() is derived from
> 'kvm_vgic_global_state.has_gicv4_1', do we still need to depend on the
> latter?

Yes, this is a very subtle choice.

GICv4 does not support vSGIs, only vLPIs. If we omit "has_gicv4_1", we
break vLPIs on this hardware.

OTOH, GICv4.1 supports both vSGIs and vLPIs, and the dirty secret here
is we make vLPI support follow userspace's wishes for vSGIs. With that
being said, this should be predicated on both the ITS and the CPUIF
supporting vSGIs.

> Also just to double-check, there are other references that directly
> read 'kvm_vgic_global_state.has_gicv4_1' (vgic_v3_map_resources() for
> instance). Do we not want them to be replaced with
> vgic_supports_direct_sgis()?

There are a few screw ups on my part but most of the remaining checks
are for hardware support (i.e. before fiddling with the GIC), not VM
support.

diff --git a/arch/arm64/kvm/vgic/vgic-v3.c b/arch/arm64/kvm/vgic/vgic-v3.c
index b9ad7c42c5b0..13b561a2c90b 100644
--- a/arch/arm64/kvm/vgic/vgic-v3.c
+++ b/arch/arm64/kvm/vgic/vgic-v3.c
@@ -404,7 +404,7 @@ int vgic_v3_save_pending_tables(struct kvm *kvm)
 	 * The above vgic initialized check also ensures that the allocation
 	 * and enabling of the doorbells have already been done.
 	 */
-	if (kvm_vgic_global_state.has_gicv4_1) {
+	if (kvm_vgic_global_state.has_gicv4_1 && vgic_supports_direct_irqs(kvm)) {
 		unmap_all_vpes(kvm);
 		vlpi_avail = true;
 	}
@@ -581,7 +581,7 @@ int vgic_v3_map_resources(struct kvm *kvm)
 		return -EBUSY;
 	}
 
-	if (kvm_vgic_global_state.has_gicv4_1)
+	if (vgic_supports_direct_sgis(kvm))
 		vgic_v4_configure_vsgis(kvm);
 
 	return 0;
diff --git a/arch/arm64/kvm/vgic/vgic-v4.c b/arch/arm64/kvm/vgic/vgic-v4.c
index a9c772697a43..053d4fe7de8b 100644
--- a/arch/arm64/kvm/vgic/vgic-v4.c
+++ b/arch/arm64/kvm/vgic/vgic-v4.c
@@ -245,7 +245,7 @@ int vgic_v4_init(struct kvm *kvm)
 
 	lockdep_assert_held(&kvm->arch.config_lock);
 
-	if (!kvm_vgic_global_state.has_gicv4)
+	if (!vgic_supports_direct_irqs(kvm))
 		return 0; /* Nothing to see here... move along. */
 
 	if (dist->its_vm.vpes)

[PATCH v2 4/4] KVM: arm64: selftests: Add test for nASSGIcap attribute

[Oliver Upton]

From: Raghavendra Rao Ananta <rananta@google.com>

Extend vgic_init to test the nASSGIcap attribute, asserting that it is
configurable (within reason) prior to initializing the VGIC.
Additionally, check that userspace cannot set the attribute after the
VGIC has been initialized.

Signed-off-by: Raghavendra Rao Ananta <rananta@google.com>
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
---
 tools/testing/selftests/kvm/arm64/vgic_init.c | 41 +++++++++++++++++++
 1 file changed, 41 insertions(+)

diff --git a/tools/testing/selftests/kvm/arm64/vgic_init.c b/tools/testing/selftests/kvm/arm64/vgic_init.c
index b3b5fb0ff0a9..aaecba432dbc 100644
--- a/tools/testing/selftests/kvm/arm64/vgic_init.c
+++ b/tools/testing/selftests/kvm/arm64/vgic_init.c
@@ -675,6 +675,46 @@ static void test_v3_its_region(void)
 	vm_gic_destroy(&v);
 }
 
+static void test_v3_nassgicap(void)
+{
+	struct kvm_vcpu *vcpus[NR_VCPUS];
+	struct vm_gic vm;
+	__u8 nassgicap;
+	int ret;
+
+	vm = vm_gic_create_with_vcpus(KVM_DEV_TYPE_ARM_VGIC_V3, NR_VCPUS, vcpus);
+	TEST_REQUIRE(!__kvm_has_device_attr(vm.gic_fd, KVM_DEV_ARM_VGIC_GRP_FEATURES,
+					    KVM_DEV_ARM_VGIC_FEATURE_nASSGIcap));
+
+	kvm_device_attr_get(vm.gic_fd, KVM_DEV_ARM_VGIC_GRP_FEATURES,
+			    KVM_DEV_ARM_VGIC_FEATURE_nASSGIcap, &nassgicap);
+	if (!nassgicap) {
+		nassgicap = true;
+		ret = __kvm_device_attr_set(vm.gic_fd, KVM_DEV_ARM_VGIC_GRP_FEATURES,
+					    KVM_DEV_ARM_VGIC_FEATURE_nASSGIcap, &nassgicap);
+		TEST_ASSERT(ret && errno == EINVAL,
+			    "Enabled nASSGIcap even though it's unavailable");
+	} else {
+		nassgicap = false;
+		kvm_device_attr_set(vm.gic_fd, KVM_DEV_ARM_VGIC_GRP_FEATURES,
+				    KVM_DEV_ARM_VGIC_FEATURE_nASSGIcap, &nassgicap);
+
+		nassgicap = true;
+		kvm_device_attr_set(vm.gic_fd, KVM_DEV_ARM_VGIC_GRP_FEATURES,
+				    KVM_DEV_ARM_VGIC_FEATURE_nASSGIcap, &nassgicap);
+	}
+
+	kvm_device_attr_set(vm.gic_fd, KVM_DEV_ARM_VGIC_GRP_CTRL,
+			    KVM_DEV_ARM_VGIC_CTRL_INIT, NULL);
+
+	ret = __kvm_device_attr_set(vm.gic_fd, KVM_DEV_ARM_VGIC_GRP_FEATURES,
+				    KVM_DEV_ARM_VGIC_FEATURE_nASSGIcap, &nassgicap);
+	TEST_ASSERT(ret && errno == EBUSY,
+		    "Configured nASSGIcap after initializing the VGIC");
+
+	vm_gic_destroy(&vm);
+}
+
 /*
  * Returns 0 if it's possible to create GIC device of a given type (V2 or V3).
  */
@@ -730,6 +770,7 @@ void run_tests(uint32_t gic_dev_type)
 		test_v3_last_bit_single_rdist();
 		test_v3_redist_ipa_range_check_at_vcpu_run();
 		test_v3_its_region();
+		test_v3_nassgicap();
 	}
 }
 
-- 
2.39.5

Re: [PATCH v2 4/4] KVM: arm64: selftests: Add test for nASSGIcap attribute

[Raghavendra Rao Ananta]

On Fri, May 30, 2025 at 6:26 PM Oliver Upton <oliver.upton@linux.dev> wrote:
>
> From: Raghavendra Rao Ananta <rananta@google.com>
>
> Extend vgic_init to test the nASSGIcap attribute, asserting that it is
> configurable (within reason) prior to initializing the VGIC.
> Additionally, check that userspace cannot set the attribute after the
> VGIC has been initialized.
>
> Signed-off-by: Raghavendra Rao Ananta <rananta@google.com>
> Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
> ---
>  tools/testing/selftests/kvm/arm64/vgic_init.c | 41 +++++++++++++++++++
>  1 file changed, 41 insertions(+)
>
> diff --git a/tools/testing/selftests/kvm/arm64/vgic_init.c b/tools/testing/selftests/kvm/arm64/vgic_init.c
> index b3b5fb0ff0a9..aaecba432dbc 100644
> --- a/tools/testing/selftests/kvm/arm64/vgic_init.c
> +++ b/tools/testing/selftests/kvm/arm64/vgic_init.c
> @@ -675,6 +675,46 @@ static void test_v3_its_region(void)
>         vm_gic_destroy(&v);
>  }
>
> +static void test_v3_nassgicap(void)
> +{
> +       struct kvm_vcpu *vcpus[NR_VCPUS];
> +       struct vm_gic vm;
> +       __u8 nassgicap;
> +       int ret;
> +
> +       vm = vm_gic_create_with_vcpus(KVM_DEV_TYPE_ARM_VGIC_V3, NR_VCPUS, vcpus);
> +       TEST_REQUIRE(!__kvm_has_device_attr(vm.gic_fd, KVM_DEV_ARM_VGIC_GRP_FEATURES,
> +                                           KVM_DEV_ARM_VGIC_FEATURE_nASSGIcap));
> +
> +       kvm_device_attr_get(vm.gic_fd, KVM_DEV_ARM_VGIC_GRP_FEATURES,
> +                           KVM_DEV_ARM_VGIC_FEATURE_nASSGIcap, &nassgicap);
> +       if (!nassgicap) {
> +               nassgicap = true;
> +               ret = __kvm_device_attr_set(vm.gic_fd, KVM_DEV_ARM_VGIC_GRP_FEATURES,
> +                                           KVM_DEV_ARM_VGIC_FEATURE_nASSGIcap, &nassgicap);
> +               TEST_ASSERT(ret && errno == EINVAL,
> +                           "Enabled nASSGIcap even though it's unavailable");
> +       } else {
> +               nassgicap = false;
> +               kvm_device_attr_set(vm.gic_fd, KVM_DEV_ARM_VGIC_GRP_FEATURES,
> +                                   KVM_DEV_ARM_VGIC_FEATURE_nASSGIcap, &nassgicap);
> +
> +               nassgicap = true;
> +               kvm_device_attr_set(vm.gic_fd, KVM_DEV_ARM_VGIC_GRP_FEATURES,
> +                                   KVM_DEV_ARM_VGIC_FEATURE_nASSGIcap, &nassgicap);
> +       }
> +
> +       kvm_device_attr_set(vm.gic_fd, KVM_DEV_ARM_VGIC_GRP_CTRL,
> +                           KVM_DEV_ARM_VGIC_CTRL_INIT, NULL);
> +
> +       ret = __kvm_device_attr_set(vm.gic_fd, KVM_DEV_ARM_VGIC_GRP_FEATURES,
> +                                   KVM_DEV_ARM_VGIC_FEATURE_nASSGIcap, &nassgicap);
> +       TEST_ASSERT(ret && errno == EBUSY,
> +                   "Configured nASSGIcap after initializing the VGIC");
> +
> +       vm_gic_destroy(&vm);
> +}
> +
>  /*
>   * Returns 0 if it's possible to create GIC device of a given type (V2 or V3).
>   */
> @@ -730,6 +770,7 @@ void run_tests(uint32_t gic_dev_type)
>                 test_v3_last_bit_single_rdist();
>                 test_v3_redist_ipa_range_check_at_vcpu_run();
>                 test_v3_its_region();
> +               test_v3_nassgicap();
>         }
>  }
>
> --
> 2.39.5
>

Reviewed-by: Raghavendra Rao Ananta <rananta@google.com>