[PATCH v2 36/36] KVM: arm64: gic-v5: Communicate userspace-drivable PPIs via a UAPI

[Sascha Bischoff]

On Wed, 2026-01-07 at 16:51 +0000, Jonathan Cameron wrote:
> On Fri, 19 Dec 2025 15:52:48 +0000
> Sascha Bischoff <Sascha.Bischoff at arm.com> wrote:
> 
> > GICv5 systems will likely not support the full set of PPIs. The
> > presence of any virtual PPI is tied to the presence of the physical
> > PPI. Therefore, the available PPIs will be limited by the physical
> > host. Userspace cannot drive any PPIs that are not implemented.
> > 
> > Moreover, it is not desirable to expose all PPIs to the guest in
> > the
> > first place, even if they are supported in hardware. Some devices,
> > such as the arch timer, are implemented in KVM, and hence those
> > PPIs
> > shouldn't be driven by userspace, either.
> > 
> > Provided a new UAPI:
> >   KVM_DEV_ARM_VGIC_GRP_CTRL => KVM_DEV_ARM_VGIC_USERPSPACE_PPIs
> > 
> > This allows userspace to query which PPIs it is able to drive via
> > KVM_IRQ_LINE.
> > 
> > Signed-off-by: Sascha Bischoff <sascha.bischoff at arm.com>
> 
> A couple of trivial comments on this patch.
> 
> Overall, to me as a definite non expert in kvm GIC emulation this
> series looks to be in a pretty good state.
> 
> Thanks,
> 
> Jonathan

This seems like as good a place as any to thank you for all of the
reviews. They have been really helpful in getting is series to a better
state. Thanks a lot for taking the time!

(+ some responses inline)

Sascha

> > ---
> >  .../virt/kvm/devices/arm-vgic-v5.rst          | 13 ++++++++++
> >  arch/arm64/include/uapi/asm/kvm.h             |  1 +
> >  arch/arm64/kvm/vgic/vgic-kvm-device.c         | 25
> > +++++++++++++++++++
> >  arch/arm64/kvm/vgic/vgic-v5.c                 |  8 ++++++
> >  include/kvm/arm_vgic.h                        |  5 ++++
> >  include/linux/irqchip/arm-gic-v5.h            |  4 +++
> >  tools/arch/arm64/include/uapi/asm/kvm.h       |  1 +
> >  7 files changed, 57 insertions(+)
> > 
> > diff --git a/Documentation/virt/kvm/devices/arm-vgic-v5.rst
> > b/Documentation/virt/kvm/devices/arm-vgic-v5.rst
> > index 9904cb888277d..d9f2917b609c5 100644
> > --- a/Documentation/virt/kvm/devices/arm-vgic-v5.rst
> > +++ b/Documentation/virt/kvm/devices/arm-vgic-v5.rst
> > @@ -25,6 +25,19 @@ Groups:
> >        request the initialization of the VGIC, no additional
> > parameter in
> >        kvm_device_attr.addr. Must be called after all VCPUs have
> > been created.
> >  
> > +   KVM_DEV_ARM_VGIC_USERPSPACE_PPIs
> > +      request the mask of userspace-drivable PPIs. Only a subset
> > of the PPIs can
> > +      be directly driven from userspace with GICv5, and the
> > returned mask
> > +      informs userspace of which it is allowed to drive via
> > KVM_IRQ_LINE.
> > +
> > +      Userspace must allocate and point to __u64[2] with of data
> > in
> 
> with of?

Fixed ("with" was meant to be "worth", but I just dropped that and went
with "of").

> 
> > +      kvm_device_attr.addr. When this call returns, the provided
> > memory will be
> > +      populated with the userspace PPI mask. The lower __u64
> > contains the mask
> > +      for the lower 64 PPIS, with the remaining 64 being in the
> > second __u64.
> > +
> > +      This is a read-only attribute, and cannot be set. Attempts
> > to set it are
> > +      rejected.
> > +
> >    Errors:
> >  
> >      ======= 
> > ========================================================
> 
> > diff --git a/arch/arm64/kvm/vgic/vgic-kvm-device.c
> > b/arch/arm64/kvm/vgic/vgic-kvm-device.c
> > index 78903182bba08..360c78ed4f104 100644
> > --- a/arch/arm64/kvm/vgic/vgic-kvm-device.c
> > +++ b/arch/arm64/kvm/vgic/vgic-kvm-device.c
> > @@ -719,6 +719,25 @@ struct kvm_device_ops kvm_arm_vgic_v3_ops = {
> >  	.has_attr = vgic_v3_has_attr,
> >  };
> >  
> > +static int vgic_v5_get_userspace_ppis(struct kvm_device *dev,
> > +				      struct kvm_device_attr
> > *attr)
> > +{
> > +	u64 __user *uaddr = (u64 __user *)(long)attr->addr;
> > +	struct gicv5_vm *gicv5_vm = &dev->kvm->arch.vgic.gicv5_vm;
> > +	int i, ret;
> > +
> > +	guard(mutex)(&dev->kvm->arch.config_lock);
> > +
> > +	for (i = 0; i < 2; ++i) {
> 
> Can drag declaration of i into loop init.

Done.

> Also I just noticed the series is rather random wrt to pre or post
> increment
> in cases where it doesn't matter. I'd go with post increment for for
> loops.
> I took a quick look at a random file in this directory and that's
> what is used there.

I've gone through and made them consistent.

> 
> 
> > +		ret = put_user(gicv5_vm->userspace_ppis[i],
> > uaddr);
> > +		if (ret)
> > +			return ret;
> > +		uaddr++;
> > +	}
> > +
> > +	return 0;
> > +}
> 
> > diff --git a/arch/arm64/kvm/vgic/vgic-v5.c
> > b/arch/arm64/kvm/vgic/vgic-v5.c
> > index bf72982d6a2e8..04300926683b6 100644
> > --- a/arch/arm64/kvm/vgic/vgic-v5.c
> > +++ b/arch/arm64/kvm/vgic/vgic-v5.c
> > @@ -122,6 +122,14 @@ int vgic_v5_init(struct kvm *kvm)
> >  		}
> >  	}
> >  
> > +	/*
> > +	 * We only allow userspace to drive the SW_PPI, if it is
> > +	 * implemented.
> > +	 */
> 
> 	/* We only allow userspace to drive the SW_PPI, if it is
> implemented. */
> 
> Is under 80 chars (just) so go with that.

Done.

> 
> 
> > +	kvm->arch.vgic.gicv5_vm.userspace_ppis[0] = GICV5_SW_PPI &
> > GICV5_HWIRQ_ID;
> > +	kvm->arch.vgic.gicv5_vm.userspace_ppis[0] &= ppi_caps-
> > >impl_ppi_mask[0];
> > +	kvm->arch.vgic.gicv5_vm.userspace_ppis[1] = 0;
> > +
> >  	return 0;
> >  }
> 
>