[PATCH v5 0/6] KVM: arm64: Allow userspace to write GICD_TYPER2.nASSGIcap

[PATCH v5 0/6] KVM: arm64: Allow userspace to write GICD_TYPER2.nASSGIcap

[Oliver Upton]

v4 -> v5:
 - Fix polarity of nASSGIreq masking (Ben)
 - Explicitly call out some subtle changes made in changelogs (Eric)
 - Avoid open-coding irq_is_ppi() (Eric)

Oliver Upton (4):
  KVM: arm64: Disambiguate support for vSGIs v. vLPIs
  KVM: arm64: vgic-v3: Consolidate MAINT_IRQ handling
  KVM: arm64: vgic-v3: Allow access to GICD_IIDR prior to initialization
  Documentation: KVM: arm64: Describe VGICv3 registers writable pre-init

Raghavendra Rao Ananta (2):
  KVM: arm64: vgic-v3: Allow userspace to write GICD_TYPER2.nASSGIcap
  KVM: arm64: selftests: Add test for nASSGIcap attribute

 .../virt/kvm/devices/arm-vgic-v3.rst          | 17 +++++
 arch/arm64/kvm/vgic/vgic-init.c               | 21 +++---
 arch/arm64/kvm/vgic/vgic-kvm-device.c         | 70 ++++++++++++-------
 arch/arm64/kvm/vgic/vgic-mmio-v3.c            | 33 +++++++--
 arch/arm64/kvm/vgic/vgic-v4.c                 |  4 +-
 arch/arm64/kvm/vgic/vgic.c                    |  4 +-
 arch/arm64/kvm/vgic/vgic.h                    |  8 +++
 include/kvm/arm_vgic.h                        |  3 +
 tools/testing/selftests/kvm/arm64/vgic_init.c | 42 ++++++++++-
 9 files changed, 150 insertions(+), 52 deletions(-)


base-commit: 86731a2a651e58953fc949573895f2fa6d456841
-- 
2.39.5

[PATCH v5 1/6] 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, including an
opportunistic fix to always check if the CPUIF is capable of handling
vSGIs.

Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
---
 arch/arm64/kvm/vgic/vgic-init.c    |  9 ++++-----
 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, 25 insertions(+), 15 deletions(-)

diff --git a/arch/arm64/kvm/vgic/vgic-init.c b/arch/arm64/kvm/vgic/vgic-init.c
index eb1205654ac8..0d8bc2ac627a 100644
--- a/arch/arm64/kvm/vgic/vgic-init.c
+++ b/arch/arm64/kvm/vgic/vgic-init.c
@@ -391,11 +391,10 @@ int vgic_init(struct kvm *kvm)
 		goto out;
 
 	/*
-	 * If we have GICv4.1 enabled, unconditionally request enable the
-	 * v4 support so that we get HW-accelerated vSGIs. Otherwise, only
-	 * enable it if we present a virtual ITS to the guest.
+	 * Ensure vPEs are allocated if direct IRQ injection (e.g. vSGIs,
+	 * vLPIs) is supported.
 	 */
-	if (vgic_supports_direct_msis(kvm)) {
+	if (vgic_supports_direct_irqs(kvm)) {
 		ret = vgic_v4_init(kvm);
 		if (ret)
 			goto out;
@@ -443,7 +442,7 @@ 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..8f0f460b6a61 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 193946108192..e7e284d47a77 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 v5 2/6] 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. As this is now handled separately from the VGIC
registers, the locking is relaxed to only acquire the intended
config_lock.

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 f9ae790163fb..00c011cc8627 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 (!irq_is_ppi(val))
+			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 v5 3/6] KVM: arm64: vgic-v3: Allow access to GICD_IIDR prior to initialization

[Oliver Upton]

KVM allows userspace to write GICD_IIDR for backwards-compatibility with
older kernels, where new implementation revisions have new features.
Unfortunately this is allowed to happen at runtime, and ripping features
out from underneath a running guest is a terrible idea.

While we can't do anything about the ABI, prepare for more ID-like
registers by allowing access to GICD_IIDR prior to VGIC initialization.
Hoist initializaiton of the default value to kvm_vgic_create() and
discard the incorrect comment that assumed userspace could access the
register before initialization (until now).

Subsequent changes will allow the VMM to further provision the GIC
feature set, e.g. the presence of nASSGIcap.

Reviewed-by: Eric Auger <eric.auger@redhat.com>
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
---
 arch/arm64/kvm/vgic/vgic-init.c       |  9 +--------
 arch/arm64/kvm/vgic/vgic-kvm-device.c | 20 +++++++++++++++++++-
 2 files changed, 20 insertions(+), 9 deletions(-)

diff --git a/arch/arm64/kvm/vgic/vgic-init.c b/arch/arm64/kvm/vgic/vgic-init.c
index 0d8bc2ac627a..31462ba093c9 100644
--- a/arch/arm64/kvm/vgic/vgic-init.c
+++ b/arch/arm64/kvm/vgic/vgic-init.c
@@ -157,6 +157,7 @@ int kvm_vgic_create(struct kvm *kvm, u32 type)
 
 	kvm->arch.vgic.in_kernel = true;
 	kvm->arch.vgic.vgic_model = type;
+	kvm->arch.vgic.implementation_rev = KVM_VGIC_IMP_REV_LATEST;
 
 	kvm->arch.vgic.vgic_dist_base = VGIC_ADDR_UNDEF;
 
@@ -408,15 +409,7 @@ int vgic_init(struct kvm *kvm)
 		goto out;
 
 	vgic_debug_init(kvm);
-
-	/*
-	 * If userspace didn't set the GIC implementation revision,
-	 * default to the latest and greatest. You know want it.
-	 */
-	if (!dist->implementation_rev)
-		dist->implementation_rev = KVM_VGIC_IMP_REV_LATEST;
 	dist->initialized = true;
-
 out:
 	return ret;
 }
diff --git a/arch/arm64/kvm/vgic/vgic-kvm-device.c b/arch/arm64/kvm/vgic/vgic-kvm-device.c
index 00c011cc8627..8e24d550d9d2 100644
--- a/arch/arm64/kvm/vgic/vgic-kvm-device.c
+++ b/arch/arm64/kvm/vgic/vgic-kvm-device.c
@@ -5,6 +5,7 @@
  * Copyright (C) 2015 ARM Ltd.
  * Author: Marc Zyngier <marc.zyngier@arm.com>
  */
+#include <linux/irqchip/arm-gic-v3.h>
 #include <linux/kvm_host.h>
 #include <kvm/arm_vgic.h>
 #include <linux/uaccess.h>
@@ -503,6 +504,23 @@ int vgic_v3_parse_attr(struct kvm_device *dev, struct kvm_device_attr *attr,
 	return 0;
 }
 
+/*
+ * Allow access to certain ID-like registers prior to VGIC initialization,
+ * thereby allowing the VMM to provision the features / sizing of the VGIC.
+ */
+static bool reg_allowed_pre_init(struct kvm_device_attr *attr)
+{
+	if (attr->group != KVM_DEV_ARM_VGIC_GRP_DIST_REGS)
+		return false;
+
+	switch (attr->attr & KVM_DEV_ARM_VGIC_OFFSET_MASK) {
+	case GICD_IIDR:
+		return true;
+	default:
+		return false;
+	}
+}
+
 /*
  * vgic_v3_attr_regs_access - allows user space to access VGIC v3 state
  *
@@ -552,7 +570,7 @@ static int vgic_v3_attr_regs_access(struct kvm_device *dev,
 
 	mutex_lock(&dev->kvm->arch.config_lock);
 
-	if (!vgic_initialized(dev->kvm)) {
+	if (!(vgic_initialized(dev->kvm) || reg_allowed_pre_init(attr))) {
 		ret = -EBUSY;
 		goto out;
 	}
-- 
2.39.5

[PATCH v5 4/6] KVM: arm64: vgic-v3: Allow userspace to write 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>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
---
 arch/arm64/kvm/vgic/vgic-init.c       |  3 +++
 arch/arm64/kvm/vgic/vgic-kvm-device.c |  1 +
 arch/arm64/kvm/vgic/vgic-mmio-v3.c    | 19 +++++++++++++++++--
 arch/arm64/kvm/vgic/vgic.h            |  1 +
 include/kvm/arm_vgic.h                |  3 +++
 5 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/kvm/vgic/vgic-init.c b/arch/arm64/kvm/vgic/vgic-init.c
index 31462ba093c9..6ec3535e142c 100644
--- a/arch/arm64/kvm/vgic/vgic-init.c
+++ b/arch/arm64/kvm/vgic/vgic-init.c
@@ -166,6 +166,9 @@ int kvm_vgic_create(struct kvm *kvm, u32 type)
 	else
 		INIT_LIST_HEAD(&kvm->arch.vgic.rd_regions);
 
+	if (type == KVM_DEV_TYPE_ARM_VGIC_V3)
+		kvm->arch.vgic.nassgicap = system_supports_direct_sgis();
+
 out_unlock:
 	mutex_unlock(&kvm->arch.config_lock);
 	kvm_unlock_all_vcpus(kvm);
diff --git a/arch/arm64/kvm/vgic/vgic-kvm-device.c b/arch/arm64/kvm/vgic/vgic-kvm-device.c
index 8e24d550d9d2..3d1a776b716d 100644
--- a/arch/arm64/kvm/vgic/vgic-kvm-device.c
+++ b/arch/arm64/kvm/vgic/vgic-kvm-device.c
@@ -515,6 +515,7 @@ static bool reg_allowed_pre_init(struct kvm_device_attr *attr)
 
 	switch (attr->attr & KVM_DEV_ARM_VGIC_OFFSET_MASK) {
 	case GICD_IIDR:
+	case GICD_TYPER2:
 		return true;
 	default:
 		return false;
diff --git a/arch/arm64/kvm/vgic/vgic-mmio-v3.c b/arch/arm64/kvm/vgic/vgic-mmio-v3.c
index 8f0f460b6a61..a3ef185209e9 100644
--- a/arch/arm64/kvm/vgic/vgic-mmio-v3.c
+++ b/arch/arm64/kvm/vgic/vgic-mmio-v3.c
@@ -53,11 +53,16 @@ bool vgic_supports_direct_msis(struct kvm *kvm)
 	return kvm_vgic_global_state.has_gicv4 && vgic_has_its(kvm);
 }
 
-bool vgic_supports_direct_sgis(struct kvm *kvm)
+bool system_supports_direct_sgis(void)
 {
 	return kvm_vgic_global_state.has_gicv4_1 && gic_cpuif_has_vsgi();
 }
 
+bool vgic_supports_direct_sgis(struct kvm *kvm)
+{
+	return kvm->arch.vgic.nassgicap;
+}
+
 /*
  * The Revision field in the IIDR have the following meanings:
  *
@@ -163,8 +168,18 @@ static int vgic_mmio_uaccess_write_v3_misc(struct kvm_vcpu *vcpu,
 
 	switch (addr & 0x0c) {
 	case GICD_TYPER2:
-		if (val != vgic_mmio_read_v3_misc(vcpu, addr, len))
+		reg = vgic_mmio_read_v3_misc(vcpu, addr, len);
+
+		if (reg == val)
+			return 0;
+		if (vgic_initialized(vcpu->kvm))
+			return -EBUSY;
+		if ((reg ^ val) & ~GICD_TYPER2_nASSGIcap)
 			return -EINVAL;
+		if (!system_supports_direct_sgis() && val)
+			return -EINVAL;
+
+		dist->nassgicap = val & GICD_TYPER2_nASSGIcap;
 		return 0;
 	case GICD_IIDR:
 		reg = vgic_mmio_read_v3_misc(vcpu, addr, len);
diff --git a/arch/arm64/kvm/vgic/vgic.h b/arch/arm64/kvm/vgic/vgic.h
index ebf9ed6adeac..96048ec59d0d 100644
--- a/arch/arm64/kvm/vgic/vgic.h
+++ b/arch/arm64/kvm/vgic/vgic.h
@@ -369,6 +369,7 @@ void vgic_its_invalidate_all_caches(struct kvm *kvm);
 int vgic_its_inv_lpi(struct kvm *kvm, struct vgic_irq *irq);
 int vgic_its_invall(struct kvm_vcpu *vcpu);
 
+bool system_supports_direct_sgis(void);
 bool vgic_supports_direct_msis(struct kvm *kvm);
 bool vgic_supports_direct_sgis(struct kvm *kvm);
 
diff --git a/include/kvm/arm_vgic.h b/include/kvm/arm_vgic.h
index 4a34f7f0a864..1b4886f3fb20 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 v5 4/6] KVM: arm64: vgic-v3: Allow userspace to write GICD_TYPER2.nASSGIcap

[Raghavendra Rao Ananta]

Hi Oliver,

On Wed, Jul 23, 2025 at 11:28 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.
>
Is the "bundling vLPI and vSGI" part missing from this series? Unless
I'm using a wrong base, we call vgic_v4_init() if
vgic_supports_direct_irqs(), which will be true even if userspace
turned off GICD_TYPER2.nASSGIcap. Am I missing something?

Thank you.
Raghavendra

Re: [PATCH v5 4/6] KVM: arm64: vgic-v3: Allow userspace to write GICD_TYPER2.nASSGIcap

[Oliver Upton]

On Fri, Jul 25, 2025 at 03:53:23PM -0700, Raghavendra Rao Ananta wrote:
> Hi Oliver,
> 
> On Wed, Jul 23, 2025 at 11:28 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.
> >
> Is the "bundling vLPI and vSGI" part missing from this series? Unless
> I'm using a wrong base, we call vgic_v4_init() if
> vgic_supports_direct_irqs(), which will be true even if userspace
> turned off GICD_TYPER2.nASSGIcap. Am I missing something?

Nope, squashing this into the patch:

diff --git a/arch/arm64/kvm/vgic/vgic.h b/arch/arm64/kvm/vgic/vgic.h
index 96048ec59d0d..fb6d7c098ae6 100644
--- a/arch/arm64/kvm/vgic/vgic.h
+++ b/arch/arm64/kvm/vgic/vgic.h
@@ -375,7 +375,15 @@ 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);
+	/*
+	 * 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 (system_supports_direct_sgis())
+		return vgic_supports_direct_sgis(kvm);
+
+	return vgic_supports_direct_msis(kvm);
 }
 
 int vgic_v4_init(struct kvm *kvm);

[PATCH v5 5/6] 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>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
---
 tools/testing/selftests/kvm/arm64/vgic_init.c | 42 ++++++++++++++++++-
 1 file changed, 40 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/kvm/arm64/vgic_init.c b/tools/testing/selftests/kvm/arm64/vgic_init.c
index b3b5fb0ff0a9..743351aa998e 100644
--- a/tools/testing/selftests/kvm/arm64/vgic_init.c
+++ b/tools/testing/selftests/kvm/arm64/vgic_init.c
@@ -13,13 +13,12 @@
 #include "kvm_util.h"
 #include "processor.h"
 #include "vgic.h"
+#include "gic_v3.h"
 
 #define NR_VCPUS		4
 
 #define REG_OFFSET(vcpu, offset) (((uint64_t)vcpu << 32) | offset)
 
-#define GICR_TYPER 0x8
-
 #define VGIC_DEV_IS_V2(_d) ((_d) == KVM_DEV_TYPE_ARM_VGIC_V2)
 #define VGIC_DEV_IS_V3(_d) ((_d) == KVM_DEV_TYPE_ARM_VGIC_V3)
 
@@ -675,6 +674,44 @@ static void test_v3_its_region(void)
 	vm_gic_destroy(&v);
 }
 
+static void test_v3_nassgicap(void)
+{
+	struct kvm_vcpu *vcpus[NR_VCPUS];
+	bool has_nassgicap;
+	struct vm_gic vm;
+	u32 typer2;
+	int ret;
+
+	vm = vm_gic_create_with_vcpus(KVM_DEV_TYPE_ARM_VGIC_V3, NR_VCPUS, vcpus);
+	kvm_device_attr_get(vm.gic_fd, KVM_DEV_ARM_VGIC_GRP_DIST_REGS,
+			    GICD_TYPER2, &typer2);
+	has_nassgicap = typer2 & GICD_TYPER2_nASSGIcap;
+
+	typer2 |= GICD_TYPER2_nASSGIcap;
+	ret = __kvm_device_attr_set(vm.gic_fd, KVM_DEV_ARM_VGIC_GRP_DIST_REGS,
+				    GICD_TYPER2, &typer2);
+	if (has_nassgicap)
+		TEST_ASSERT(!ret, KVM_IOCTL_ERROR(KVM_DEVICE_ATTR_SET, ret));
+	else
+		TEST_ASSERT(ret && errno == EINVAL,
+			    "Enabled nASSGIcap even though it's unavailable");
+
+	typer2 &= ~GICD_TYPER2_nASSGIcap;
+	kvm_device_attr_set(vm.gic_fd, KVM_DEV_ARM_VGIC_GRP_DIST_REGS,
+			    GICD_TYPER2, &typer2);
+
+	kvm_device_attr_set(vm.gic_fd, KVM_DEV_ARM_VGIC_GRP_CTRL,
+			    KVM_DEV_ARM_VGIC_CTRL_INIT, NULL);
+
+	typer2 ^= GICD_TYPER2_nASSGIcap;
+	ret = __kvm_device_attr_set(vm.gic_fd, KVM_DEV_ARM_VGIC_GRP_DIST_REGS,
+				    GICD_TYPER2, &typer2);
+	TEST_ASSERT(ret && errno == EBUSY,
+		    "Changed 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 +767,7 @@ 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

[PATCH v5 6/6] Documentation: KVM: arm64: Describe VGICv3 registers writable pre-init

[Oliver Upton]

KVM allows userspace to control GICD_IIDR.Revision and
GICD_TYPER2.nASSGIcap prior to initialization for the sake of
provisioning the guest-visible feature set. Document the userspace
expectations surrounding accesses to these registers.

Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
---
 Documentation/virt/kvm/devices/arm-vgic-v3.rst | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/Documentation/virt/kvm/devices/arm-vgic-v3.rst b/Documentation/virt/kvm/devices/arm-vgic-v3.rst
index e860498b1e35..c7a1cd22d814 100644
--- a/Documentation/virt/kvm/devices/arm-vgic-v3.rst
+++ b/Documentation/virt/kvm/devices/arm-vgic-v3.rst
@@ -78,6 +78,8 @@ Groups:
     -ENXIO   The group or attribute is unknown/unsupported for this device
              or hardware support is missing.
     -EFAULT  Invalid user pointer for attr->addr.
+    -EBUSY   Attempt to write a register that is read-only after
+             initialization
     =======  =============================================================
 
 
@@ -120,6 +122,15 @@ Groups:
     Note that distributor fields are not banked, but return the same value
     regardless of the mpidr used to access the register.
 
+    Userspace is allowed to write the following register fields prior to
+    initialization of the VGIC:
+
+      =====================
+      GICD_IIDR.Revision
+      GICD_TYPER2.nASSGIcap
+      =====================
+
+
     GICD_IIDR.Revision is updated when the KVM implementation is changed in a
     way directly observable by the guest or userspace.  Userspace should read
     GICD_IIDR from KVM and write back the read value to confirm its expected
@@ -128,6 +139,12 @@ Groups:
     behavior.
 
 
+    GICD_TYPER2.nASSGIcap allows userspace to control the support of SGIs
+    without an active state. At VGIC creation the field resets to the
+    maximum capability of the system. Userspace is expected to read the field
+    to determine the supported value(s) before writing to the field.
+
+
     The GICD_STATUSR and GICR_STATUSR registers are architecturally defined such
     that a write of a clear bit has no effect, whereas a write with a set bit
     clears that value.  To allow userspace to freely set the values of these two
-- 
2.39.5

Re: [PATCH v5 0/6] KVM: arm64: Allow userspace to write GICD_TYPER2.nASSGIcap

[Marc Zyngier]

On Thu, 24 Jul 2025 07:27:59 +0100,
Oliver Upton <oliver.upton@linux.dev> wrote:
> 
> v4 -> v5:
>  - Fix polarity of nASSGIreq masking (Ben)
>  - Explicitly call out some subtle changes made in changelogs (Eric)
>  - Avoid open-coding irq_is_ppi() (Eric)
> 
> Oliver Upton (4):
>   KVM: arm64: Disambiguate support for vSGIs v. vLPIs
>   KVM: arm64: vgic-v3: Consolidate MAINT_IRQ handling
>   KVM: arm64: vgic-v3: Allow access to GICD_IIDR prior to initialization
>   Documentation: KVM: arm64: Describe VGICv3 registers writable pre-init
> 
> Raghavendra Rao Ananta (2):
>   KVM: arm64: vgic-v3: Allow userspace to write GICD_TYPER2.nASSGIcap
>   KVM: arm64: selftests: Add test for nASSGIcap attribute
> 
>  .../virt/kvm/devices/arm-vgic-v3.rst          | 17 +++++
>  arch/arm64/kvm/vgic/vgic-init.c               | 21 +++---
>  arch/arm64/kvm/vgic/vgic-kvm-device.c         | 70 ++++++++++++-------
>  arch/arm64/kvm/vgic/vgic-mmio-v3.c            | 33 +++++++--
>  arch/arm64/kvm/vgic/vgic-v4.c                 |  4 +-
>  arch/arm64/kvm/vgic/vgic.c                    |  4 +-
>  arch/arm64/kvm/vgic/vgic.h                    |  8 +++
>  include/kvm/arm_vgic.h                        |  3 +
>  tools/testing/selftests/kvm/arm64/vgic_init.c | 42 ++++++++++-
>  9 files changed, 150 insertions(+), 52 deletions(-)
> 
> 
> base-commit: 86731a2a651e58953fc949573895f2fa6d456841

Reviewed-by: Marc Zyngier <maz@kernel.org>

	M.

-- 
Without deviation from the norm, progress is not possible.

Re: [PATCH v5 0/6] KVM: arm64: Allow userspace to write GICD_TYPER2.nASSGIcap

[Eric Auger]

Hi Oliver,

On 7/24/25 8:27 AM, Oliver Upton wrote:
> v4 -> v5:
>  - Fix polarity of nASSGIreq masking (Ben)
>  - Explicitly call out some subtle changes made in changelogs (Eric)
>  - Avoid open-coding irq_is_ppi() (Eric)
> 
> Oliver Upton (4):
>   KVM: arm64: Disambiguate support for vSGIs v. vLPIs
>   KVM: arm64: vgic-v3: Consolidate MAINT_IRQ handling
>   KVM: arm64: vgic-v3: Allow access to GICD_IIDR prior to initialization
>   Documentation: KVM: arm64: Describe VGICv3 registers writable pre-init

Reviewed-by: Eric Auger <eric.auger@redhat.com>

Thanks

Eric
> 
> Raghavendra Rao Ananta (2):
>   KVM: arm64: vgic-v3: Allow userspace to write GICD_TYPER2.nASSGIcap
>   KVM: arm64: selftests: Add test for nASSGIcap attribute
> 
>  .../virt/kvm/devices/arm-vgic-v3.rst          | 17 +++++
>  arch/arm64/kvm/vgic/vgic-init.c               | 21 +++---
>  arch/arm64/kvm/vgic/vgic-kvm-device.c         | 70 ++++++++++++-------
>  arch/arm64/kvm/vgic/vgic-mmio-v3.c            | 33 +++++++--
>  arch/arm64/kvm/vgic/vgic-v4.c                 |  4 +-
>  arch/arm64/kvm/vgic/vgic.c                    |  4 +-
>  arch/arm64/kvm/vgic/vgic.h                    |  8 +++
>  include/kvm/arm_vgic.h                        |  3 +
>  tools/testing/selftests/kvm/arm64/vgic_init.c | 42 ++++++++++-
>  9 files changed, 150 insertions(+), 52 deletions(-)
> 
> 
> base-commit: 86731a2a651e58953fc949573895f2fa6d456841

Re: [PATCH v5 0/6] KVM: arm64: Allow userspace to write GICD_TYPER2.nASSGIcap

[Oliver Upton]

On Wed, 23 Jul 2025 23:27:59 -0700, Oliver Upton wrote:
> v4 -> v5:
>  - Fix polarity of nASSGIreq masking (Ben)
>  - Explicitly call out some subtle changes made in changelogs (Eric)
>  - Avoid open-coding irq_is_ppi() (Eric)
> 
> Oliver Upton (4):
>   KVM: arm64: Disambiguate support for vSGIs v. vLPIs
>   KVM: arm64: vgic-v3: Consolidate MAINT_IRQ handling
>   KVM: arm64: vgic-v3: Allow access to GICD_IIDR prior to initialization
>   Documentation: KVM: arm64: Describe VGICv3 registers writable pre-init
> 
> [...]

Applied to next, thanks!

[1/6] KVM: arm64: Disambiguate support for vSGIs v. vLPIs
      https://git.kernel.org/kvmarm/kvmarm/c/82221a4e66f0
[2/6] KVM: arm64: vgic-v3: Consolidate MAINT_IRQ handling
      https://git.kernel.org/kvmarm/kvmarm/c/ef364c5b4357
[3/6] KVM: arm64: vgic-v3: Allow access to GICD_IIDR prior to initialization
      https://git.kernel.org/kvmarm/kvmarm/c/f26e6af75782
[4/6] KVM: arm64: vgic-v3: Allow userspace to write GICD_TYPER2.nASSGIcap
      https://git.kernel.org/kvmarm/kvmarm/c/c652887a9288
[5/6] KVM: arm64: selftests: Add test for nASSGIcap attribute
      https://git.kernel.org/kvmarm/kvmarm/c/15b5964a411f
[6/6] Documentation: KVM: arm64: Describe VGICv3 registers writable pre-init
      https://git.kernel.org/kvmarm/kvmarm/c/eed9b1420907

--
Best,
Oliver