[PATCH v4 10/36] KVM: arm64: gic-v5: Detect implemented PPIs on boot

[Sascha Bischoff]

On Fri, 2026-01-30 at 11:03 +0000, Marc Zyngier wrote:
> On Wed, 28 Jan 2026 18:01:54 +0000,
> Sascha Bischoff <Sascha.Bischoff at arm.com> wrote:
> > 
> > As part of booting the system and initialising KVM, create and
> > populate a mask of the implemented PPIs. This mask allows future
> > PPI
> > operations (such as save/restore or state, or syncing back into the
> > shadow state) to only consider PPIs that are actually implemented
> > on
> > the host.
> > 
> > The set of implemented virtual PPIs matches the set of implemented
> > physical PPIs for a GICv5 host. Therefore, this mask represents all
> > PPIs that could ever by used by a GICv5-based guest on a specific
> > host.
> > 
> > Only architected PPIs are currently supported in KVM with
> > GICv5. Moreover, as KVM only supports a subset of all possible PPIS
> > (Timers, PMU, GICv5 SW_PPI) the PPI mask only includes these PPIs,
> > if
> > present. The timers are always assumed to be present; if we have
> > KVM
> > we have EL2, which means that we have the EL1 & EL2 Timer PPIs. If
> > we
> > have a PMU (v3), then the PMUIRQ is present. The GICv5 SW_PPI is
> > always assumed to be present.
> > 
> > Signed-off-by: Sascha Bischoff <sascha.bischoff at arm.com>
> > ---
> >  arch/arm64/kvm/vgic/vgic-init.c    |  4 ++++
> >  arch/arm64/kvm/vgic/vgic-v5.c      | 33
> > ++++++++++++++++++++++++++++++
> >  arch/arm64/kvm/vgic/vgic.h         |  1 +
> >  include/kvm/arm_vgic.h             |  5 +++++
> >  include/linux/irqchip/arm-gic-v5.h | 10 +++++++++
> >  5 files changed, 53 insertions(+)
> > 
> > diff --git a/arch/arm64/kvm/vgic/vgic-init.c
> > b/arch/arm64/kvm/vgic/vgic-init.c
> > index 86c149537493..653364299154 100644
> > --- a/arch/arm64/kvm/vgic/vgic-init.c
> > +++ b/arch/arm64/kvm/vgic/vgic-init.c
> > @@ -750,5 +750,9 @@ int kvm_vgic_hyp_init(void)
> >  	}
> >  
> >  	kvm_info("vgic interrupt IRQ%d\n",
> > kvm_vgic_global_state.maint_irq);
> > +
> > +	/* Always safe to call */
> > +	vgic_v5_get_implemented_ppis();
> 
> What is the reason for calling this from the generic code, while it
> is
> v5-specific? I'd have expected this to be entirely contained in the
> v5
> subsystem.

At this point, I don't think that there is a reason anymore.
Previously, it somehow made more sense to me to do it like this
(although, I do fail to see why I thought that was the case at the
time). I've just reworked this to be called as part of probe (and made
it static in the process).

> 
> 
> > +
> >  	return 0;
> >  }
> > diff --git a/arch/arm64/kvm/vgic/vgic-v5.c
> > b/arch/arm64/kvm/vgic/vgic-v5.c
> > index 23d0a495d855..9bd5a85ba203 100644
> > --- a/arch/arm64/kvm/vgic/vgic-v5.c
> > +++ b/arch/arm64/kvm/vgic/vgic-v5.c
> > @@ -8,6 +8,8 @@
> >  
> >  #include "vgic.h"
> >  
> > +static struct vgic_v5_ppi_caps *ppi_caps;
> > +
> >  /*
> >   * Probe for a vGICv5 compatible interrupt controller, returning 0
> > on success.
> >   * Currently only supports GICv3-based VMs on a GICv5 host, and
> > hence only
> > @@ -53,3 +55,34 @@ int vgic_v5_probe(const struct gic_kvm_info
> > *info)
> >  
> >  	return 0;
> >  }
> > +
> > +/*
> > + * Not all PPIs are guaranteed to be implemented for GICv5.
> > Deterermine which
> > + * ones are, and generate a mask.
> > + */
> > +void vgic_v5_get_implemented_ppis(void)
> > +{
> > +	if (!cpus_have_final_cap(ARM64_HAS_GICV5_CPUIF))
> > +		return;
> > +
> > +	/* Never freed again */
> > +	ppi_caps = kzalloc(sizeof(*ppi_caps), GFP_KERNEL);
> > +	if (!ppi_caps)
> > +		return;
> 
> Maybe we can spare the call by statically allocating the PPI
> structure? Just the code calling kzalloc() costs us more than the 128
> bits required by the structure.

Yeah, it doesn't really save us anything. I've dropped the dynamic
allocation and made it static instead.

Thanks,
Sascha

> 
> Thanks,
> 
> 	M.
>