[PATCH v5 12/49] KVM: arm64: gic-v5: Keep GICv5 vCPU limit model-specific
Sascha Bischoff
Sascha.Bischoff at arm.com
Fri Aug 7 04:18:42 PDT 2026
A GICv5 host with FEAT_GCIE_LEGACY can expose either a native vGICv5
or a vGICv3 device. These models do not necessarily have the same vCPU
limit: the native GICv5 limit is probed from the IRS VPE capacity,
while the GICv3 limit remains the fixed KVM vGICv3 limit.
Keep the IRS-derived limit separately for vGICv5 creation. The
pre-VGIC KVM_CAP_MAX_VCPUS value continues to expose the largest limit
among the still-selectable models, and kvm_vgic_create() clamps the VM
to the limit of the VGIC model userspace actually selected.
GICv5 uses the userspace-provided vcpu_id as the index into the VPET,
and therefore as the VPE ID visible to the guest. Enforce the GICv5
limit against individual vCPU IDs as well as the number of vCPUs.
Reject vGICv5 creation if an existing vCPU ID cannot be represented,
and reject an out-of-range vCPU created after userspace has selected
vGICv5.
Signed-off-by: Sascha Bischoff <sascha.bischoff at arm.com>
---
arch/arm64/kvm/vgic/vgic-init.c | 53 ++++++++++++++++++++++++++-------
arch/arm64/kvm/vgic/vgic-v5.c | 16 +++++-----
include/kvm/arm_vgic.h | 16 +++++++---
3 files changed, 64 insertions(+), 21 deletions(-)
diff --git a/arch/arm64/kvm/vgic/vgic-init.c b/arch/arm64/kvm/vgic/vgic-init.c
index 079a57c2b18f6..8e1e844ed6e93 100644
--- a/arch/arm64/kvm/vgic/vgic-init.c
+++ b/arch/arm64/kvm/vgic/vgic-init.c
@@ -129,13 +129,34 @@ int kvm_vgic_create(struct kvm *kvm, u32 type)
}
ret = 0;
- if (type == KVM_DEV_TYPE_ARM_VGIC_V2)
+ switch (type) {
+ case KVM_DEV_TYPE_ARM_VGIC_V2:
kvm->max_vcpus = VGIC_V2_MAX_CPUS;
- else if (type == KVM_DEV_TYPE_ARM_VGIC_V3)
+ break;
+ case KVM_DEV_TYPE_ARM_VGIC_V3:
kvm->max_vcpus = VGIC_V3_MAX_CPUS;
- else if (type == KVM_DEV_TYPE_ARM_VGIC_V5)
- kvm->max_vcpus = min(VGIC_V5_MAX_CPUS,
- kvm_vgic_global_state.max_gic_vcpus);
+ break;
+ case KVM_DEV_TYPE_ARM_VGIC_V5:
+ kvm->max_vcpus = kvm_vgic_global_state.max_gicv5_vcpus;
+
+ /*
+ * We use the userspace-allocated vcpu_id as the index into the
+ * GICv5 VPE table. This ensures that userspace's view and the
+ * guest's view of IAFFIDs remains consistent - GICv5's virtual
+ * IAFFID is the VPE ID in that VM's VPET.
+ *
+ * Reject vGICv5 creation if we have already got any vCPUs that
+ * we cannot back with a GICv5 VPE in the VPET.
+ */
+ kvm_for_each_vcpu(i, vcpu, kvm) {
+ if (vcpu->vcpu_id >= kvm->max_vcpus) {
+ ret = -E2BIG;
+ goto out_unlock;
+ }
+ }
+
+ break;
+ }
if (atomic_read(&kvm->online_vcpus) > kvm->max_vcpus) {
ret = -E2BIG;
@@ -395,15 +416,27 @@ int kvm_vgic_vcpu_init(struct kvm_vcpu *vcpu)
if (ret)
return ret;
- /*
- * If we are creating a VCPU with a GICv3 we must also register the
- * KVM io device for the redistributor that belongs to this VCPU.
- */
- if (dist->vgic_model == KVM_DEV_TYPE_ARM_VGIC_V3) {
+ switch (dist->vgic_model) {
+ case KVM_DEV_TYPE_ARM_VGIC_V3:
+ /*
+ * If we are creating a VCPU with a GICv3 we must also register
+ * the KVM io device for the redistributor that belongs to this
+ * VCPU.
+ */
mutex_lock(&vcpu->kvm->slots_lock);
ret = vgic_register_redist_iodev(vcpu);
mutex_unlock(&vcpu->kvm->slots_lock);
+ break;
+ case KVM_DEV_TYPE_ARM_VGIC_V5:
+ /*
+ * Ensure that it is possible to represent the
+ * userspace-allocated vcpu_id in the hardware-limited (or
+ * KVM-capped) VPE table used by GICv5.
+ */
+ if (vcpu->vcpu_id >= kvm_vgic_global_state.max_gicv5_vcpus)
+ return -EINVAL;
}
+
return ret;
}
diff --git a/arch/arm64/kvm/vgic/vgic-v5.c b/arch/arm64/kvm/vgic/vgic-v5.c
index 89d39b287a615..b9257e0554b73 100644
--- a/arch/arm64/kvm/vgic/vgic-v5.c
+++ b/arch/arm64/kvm/vgic/vgic-v5.c
@@ -81,7 +81,8 @@ int vgic_v5_probe(const struct gic_kvm_info *info)
int ret;
kvm_vgic_global_state.type = VGIC_V5;
- kvm_vgic_global_state.max_gic_vcpus = VGIC_V5_MAX_CPUS;
+ kvm_vgic_global_state.max_gic_vcpus = 0;
+ kvm_vgic_global_state.max_gicv5_vcpus = 0;
kvm_vgic_global_state.vcpu_base = 0;
kvm_vgic_global_state.vctrl_base = NULL;
@@ -106,8 +107,8 @@ int vgic_v5_probe(const struct gic_kvm_info *info)
* Even if the HW supports more per-VM vCPUs, artificially cap as we
* can't use them all.
*/
- kvm_vgic_global_state.max_gic_vcpus = min(vgic_v5_irs_max_vpes(&irs_caps),
- VGIC_V5_MAX_CPUS);
+ kvm_vgic_global_state.max_gicv5_vcpus = min(vgic_v5_irs_max_vpes(&irs_caps),
+ VGIC_V5_MAX_CPUS);
/*
* GICv5 requires a set of tables to be allocated in order to manage
@@ -116,7 +117,7 @@ int vgic_v5_probe(const struct gic_kvm_info *info)
* we want to run. For now, we match the maximum number offered by the
* hardware, but this might not be a wise choice in the long term.
*/
- ret = vgic_v5_vmt_allocate(kvm_vgic_global_state.max_gic_vcpus);
+ ret = vgic_v5_vmt_allocate(kvm_vgic_global_state.max_gicv5_vcpus);
if (ret) {
kvm_err("Failed to allocate the GICv5 VM tables; no GICv5 support\n");
return -ENODEV;
@@ -151,6 +152,8 @@ int vgic_v5_probe(const struct gic_kvm_info *info)
}
v5_registered = true;
+ kvm_vgic_global_state.max_gic_vcpus =
+ kvm_vgic_global_state.max_gicv5_vcpus;
kvm_info("GCIE system register CPU interface\n");
skip_v5:
@@ -178,9 +181,8 @@ int vgic_v5_probe(const struct gic_kvm_info *info)
return v5_registered ? 0 : ret;
}
- /* We potentially limit the max VCPUs further than we need to here */
- kvm_vgic_global_state.max_gic_vcpus = min(VGIC_V3_MAX_CPUS,
- kvm_vgic_global_state.max_gic_vcpus);
+ kvm_vgic_global_state.max_gic_vcpus = max(kvm_vgic_global_state.max_gic_vcpus,
+ VGIC_V3_MAX_CPUS);
static_branch_enable(&kvm_vgic_global_state.gicv3_cpuif);
kvm_info("GCIE legacy system register CPU interface\n");
diff --git a/include/kvm/arm_vgic.h b/include/kvm/arm_vgic.h
index 7923ff20d9d7d..6d0cc38efa673 100644
--- a/include/kvm/arm_vgic.h
+++ b/include/kvm/arm_vgic.h
@@ -170,9 +170,16 @@ struct vgic_global {
/* Maintenance IRQ number */
unsigned int maint_irq;
- /* maximum number of VCPUs allowed (GICv2 limits us to 8) */
+ /*
+ * Maximum number of VCPUs exposed before userspace has selected a
+ * VGIC model. Individual VGIC models can impose a lower limit
+ * (GICv2 limits us to 8).
+ */
int max_gic_vcpus;
+ /* Maximum number of VCPUs allowed for a GICv5 VM. */
+ int max_gicv5_vcpus;
+
/* Only needed for the legacy KVM_CREATE_IRQCHIP */
bool can_emulate_gicv2;
@@ -622,10 +629,11 @@ void kvm_vgic_process_async_update(struct kvm_vcpu *vcpu);
void vgic_v3_dispatch_sgi(struct kvm_vcpu *vcpu, u64 reg, bool allow_group1);
/**
- * kvm_vgic_get_max_vcpus - Get the maximum number of VCPUs allowed by HW
+ * kvm_vgic_get_max_vcpus - Get the pre-VGIC-selection VCPU limit
*
- * The host's GIC naturally limits the maximum amount of VCPUs a guest
- * can use.
+ * Userspace can query KVM_CAP_MAX_VCPUS before selecting a VGIC model, so
+ * expose the highest model-specific limit and let kvm_vgic_create() enforce
+ * the selected model's actual limit.
*/
static inline int kvm_vgic_get_max_vcpus(void)
{
--
2.34.1
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