On Tue, 10 Jan 2023 12:17:20 +0000,
Ganapatrao Kulkarni <gankulkarni@xxxxxxxxxxxxxxxxxxxxxx> wrote:
>
> I am currently working around this with "nohlt" kernel param to
> NestedVM. Any suggestions to handle/fix this case/issue and avoid the
> slowness of booting of NestedVM with more cores?
>
> Note: Guest-Hypervisor and NestedVM are using default kernel installed
> using Fedora 36 iso.
Despite what I said earlier, I have a vague idea here, thanks to the
interesting call traces that you provided (this is really awesome work
BTW, given how hard it is to trace things across 3 different kernels).
We can slightly limit the impact of the prepare/finish sequence if the
guest hypervisor only accesses the active registers for SGIs/PPIs on
the vcpu that owns them, forbidding any cross-CPU-to-redistributor
access.
Something along these lines, which is only boot-tested. Let me know
how this fares for you.
Thanks,
M.
diff --git a/arch/arm64/kvm/vgic/vgic-mmio.c b/arch/arm64/kvm/vgic/vgic-mmio.c
index b32d434c1d4a..1cca45be5335 100644
--- a/arch/arm64/kvm/vgic/vgic-mmio.c
+++ b/arch/arm64/kvm/vgic/vgic-mmio.c
@@ -473,9 +473,10 @@ int vgic_uaccess_write_cpending(struct kvm_vcpu *vcpu,
* active state can be overwritten when the VCPU's state is synced coming back
* from the guest.
*
- * For shared interrupts as well as GICv3 private interrupts, we have to
- * stop all the VCPUs because interrupts can be migrated while we don't hold
- * the IRQ locks and we don't want to be chasing moving targets.
+ * For shared interrupts as well as GICv3 private interrupts accessed from the
+ * non-owning CPU, we have to stop all the VCPUs because interrupts can be
+ * migrated while we don't hold the IRQ locks and we don't want to be chasing
+ * moving targets.
*
* For GICv2 private interrupts we don't have to do anything because
* userspace accesses to the VGIC state already require all VCPUs to be
@@ -484,7 +485,8 @@ int vgic_uaccess_write_cpending(struct kvm_vcpu *vcpu,
*/
static void vgic_access_active_prepare(struct kvm_vcpu *vcpu, u32 intid)
{
- if (vcpu->kvm->arch.vgic.vgic_model == KVM_DEV_TYPE_ARM_VGIC_V3 ||
+ if ((vcpu->kvm->arch.vgic.vgic_model == KVM_DEV_TYPE_ARM_VGIC_V3 &&
+ vcpu == kvm_get_running_vcpu()) ||
intid >= VGIC_NR_PRIVATE_IRQS)
kvm_arm_halt_guest(vcpu->kvm);
}
@@ -492,7 +494,8 @@ static void vgic_access_active_prepare(struct kvm_vcpu *vcpu, u32 intid)
/* See vgic_access_active_prepare */
static void vgic_access_active_finish(struct kvm_vcpu *vcpu, u32 intid)
{
- if (vcpu->kvm->arch.vgic.vgic_model == KVM_DEV_TYPE_ARM_VGIC_V3 ||
+ if ((vcpu->kvm->arch.vgic.vgic_model == KVM_DEV_TYPE_ARM_VGIC_V3 &&
+ vcpu == kvm_get_running_vcpu()) ||
intid >= VGIC_NR_PRIVATE_IRQS)
kvm_arm_resume_guest(vcpu->kvm);
}
--
Without deviation from the norm, progress is not possible.
