[PATCH 18/32] KVM: arm64: gic-v5: Check for pending PPIs
Sascha Bischoff
Sascha.Bischoff at arm.com
Thu Dec 18 00:17:19 PST 2025
On Wed, 2025-12-17 at 12:00 +0000, Joey Gouly wrote:
> On Wed, Dec 17, 2025 at 11:49:32AM +0000, Joey Gouly wrote:
> > Hi Sascha,
> >
> > On Fri, Dec 12, 2025 at 03:22:41PM +0000, Sascha Bischoff wrote:
> > > This change allows KVM to check for pending PPI interrupts. This
> > > has
> > > two main components:
> > >
> > > First of all, the effective priority mask is calculated. This is
> > > a
> > > combination of the priority mask in the VPEs ICC_PCR_EL1.PRIORITY
> > > and
> > > the currently running priority as determined from the VPE's
> > > ICH_APR_EL1. If an interrupt's prioirity is greater than or equal
> > > to
> > > the effective priority mask, it can be signalled. Otherwise, it
> > > cannot.
> > >
> > > Secondly, any Enabled and Pending PPIs must be checked against
> > > this
> > > compound priority mask. The reqires the PPI priorities to by
> > > synced
> > > back to the KVM shadow state - this is skipped in general
> > > operation as
> > > it isn't required and is rather expensive. If any Enabled and
> > > Pending
> > > PPIs are of sufficient priority to be signalled, then there are
> > > pending PPIs. Else, there are not. This ensures that a VPE is
> > > not
> > > woken when it cannot actually process the pending interrupts.
> > >
> > > Signed-off-by: Sascha Bischoff <sascha.bischoff at arm.com>
> > > ---
> > > arch/arm64/kvm/vgic/vgic-v5.c | 123
> > > ++++++++++++++++++++++++++++++++++
> > > arch/arm64/kvm/vgic/vgic.c | 10 ++-
> > > arch/arm64/kvm/vgic/vgic.h | 1 +
> > > 3 files changed, 131 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/arch/arm64/kvm/vgic/vgic-v5.c
> > > b/arch/arm64/kvm/vgic/vgic-v5.c
> > > index d54595fbf4586..35740e88b3591 100644
> > > --- a/arch/arm64/kvm/vgic/vgic-v5.c
> > > +++ b/arch/arm64/kvm/vgic/vgic-v5.c
> > > @@ -54,6 +54,31 @@ int vgic_v5_probe(const struct gic_kvm_info
> > > *info)
> > > return 0;
> > > }
> > >
> > > +static u32 vgic_v5_get_effective_priority_mask(struct kvm_vcpu
> > > *vcpu)
> > > +{
> > > + struct vgic_v5_cpu_if *cpu_if = &vcpu-
> > > >arch.vgic_cpu.vgic_v5;
> > > + unsigned highest_ap, priority_mask;
> > > +
> > > + /*
> > > + * Counting the number of trailing zeros gives the
> > > current
> > > + * active priority. Explicitly use the 32-bit version
> > > here as
> > > + * we have 32 priorities. 0x20 then means that there are
> > > no
> > > + * active priorities.
> > > + */
> > > + highest_ap = __builtin_ctz(cpu_if->vgic_apr);
> >
> > __builtin_ctz(0) is undefined
> > (https://gcc.gnu.org/onlinedocs/gcc/Bit-Operation-Builtins.html)
> >
> > Looking at __vgic_v3_clear_highest_active_priority(), it handles
> > that like this:
> >
> > c0 = ap0 ? __ffs(ap0) : 32;
>
> Sorry forgot ffs() was 1-based, so:
>
> highest_ap = cpu_if->vgic_apr ? __builtin_ctz(cpu_if-
> >vgic_apr) : 32;
>
> Thanks,
> Joey
Thanks. Have made this change as I think it addresses Marc's concern
too!
Sascha
>
> >
> > Thanks,
> > Joey
> >
> > > +
> > > + /*
> > > + * An interrupt is of sufficient priority if it is equal
> > > to or
> > > + * greater than the priority mask. Add 1 to the priority
> > > mask
> > > + * (i.e., lower priority) to match the APR logic before
> > > taking
> > > + * the min. This gives us the lowest priority that is
> > > masked.
> > > + */
> > > + priority_mask = FIELD_GET(FEAT_GCIE_ICH_VMCR_EL2_VPMR,
> > > cpu_if->vgic_vmcr);
> > > + priority_mask = min(highest_ap, priority_mask + 1);
> > > +
> > > + return priority_mask;
> > > +}
> > > +
> > > static bool vgic_v5_ppi_set_pending_state(struct kvm_vcpu *vcpu,
> > > struct vgic_irq *irq)
> > > {
> > > @@ -121,6 +146,104 @@ void vgic_v5_set_ppi_ops(struct vgic_irq
> > > *irq)
> > > irq->ops = &vgic_v5_ppi_irq_ops;
> > > }
> > >
> > > +
> > > +/*
> > > + * Sync back the PPI priorities to the vgic_irq shadow state
> > > + */
> > > +static void vgic_v5_sync_ppi_priorities(struct kvm_vcpu *vcpu)
> > > +{
> > > + struct vgic_v5_cpu_if *cpu_if = &vcpu-
> > > >arch.vgic_cpu.vgic_v5;
> > > + unsigned long flags;
> > > + int i, reg;
> > > +
> > > + /* We have 16 PPI Priority regs */
> > > + for (reg = 0; reg < 16; reg++) {
> > > + const unsigned long priorityr = cpu_if-
> > > >vgic_ppi_priorityr[reg];
> > > +
> > > + for (i = 0; i < 8; ++i) {
> > > + struct vgic_irq *irq;
> > > + u32 intid;
> > > + u8 priority;
> > > +
> > > + priority = (priorityr >> (i * 8)) &
> > > 0x1f;
> > > +
> > > + intid = FIELD_PREP(GICV5_HWIRQ_TYPE,
> > > GICV5_HWIRQ_TYPE_PPI);
> > > + intid |= FIELD_PREP(GICV5_HWIRQ_ID, reg
> > > * 8 + i);
> > > +
> > > + irq = vgic_get_vcpu_irq(vcpu, intid);
> > > + raw_spin_lock_irqsave(&irq->irq_lock,
> > > flags);
> > > +
> > > + irq->priority = priority;
> > > +
> > > + raw_spin_unlock_irqrestore(&irq-
> > > >irq_lock, flags);
> > > + vgic_put_irq(vcpu->kvm, irq);
> > > + }
> > > + }
> > > +}
> > > +
> > > +bool vgic_v5_has_pending_ppi(struct kvm_vcpu *vcpu)
> > > +{
> > > + struct vgic_v5_cpu_if *cpu_if = &vcpu-
> > > >arch.vgic_cpu.vgic_v5;
> > > + unsigned long flags;
> > > + int i, reg;
> > > + unsigned int priority_mask;
> > > +
> > > + /* If no pending bits are set, exit early */
> > > + if (likely(!cpu_if->vgic_ppi_pendr[0] && !cpu_if-
> > > >vgic_ppi_pendr[1]))
> > > + return false;
> > > +
> > > + priority_mask =
> > > vgic_v5_get_effective_priority_mask(vcpu);
> > > +
> > > + /* If the combined priority mask is 0, nothing can be
> > > signalled! */
> > > + if (!priority_mask)
> > > + return false;
> > > +
> > > + /* The shadow priority is only updated on demand, sync
> > > it across first */
> > > + vgic_v5_sync_ppi_priorities(vcpu);
> > > +
> > > + for (reg = 0; reg < 2; reg++) {
> > > + unsigned long possible_bits;
> > > + const unsigned long enabler = cpu_if-
> > > >vgic_ich_ppi_enabler_exit[reg];
> > > + const unsigned long pendr = cpu_if-
> > > >vgic_ppi_pendr_exit[reg];
> > > + bool has_pending = false;
> > > +
> > > + /* Check all interrupts that are enabled and
> > > pending */
> > > + possible_bits = enabler & pendr;
> > > +
> > > + /*
> > > + * Optimisation: pending and enabled with no
> > > active priorities
> > > + */
> > > + if (possible_bits && priority_mask > 0x1f)
> > > + return true;
> > > +
> > > + for_each_set_bit(i, &possible_bits, 64) {
> > > + struct vgic_irq *irq;
> > > + u32 intid;
> > > +
> > > + intid = FIELD_PREP(GICV5_HWIRQ_TYPE,
> > > GICV5_HWIRQ_TYPE_PPI);
> > > + intid |= FIELD_PREP(GICV5_HWIRQ_ID, reg
> > > * 64 + i);
> > > +
> > > + irq = vgic_get_vcpu_irq(vcpu, intid);
> > > + raw_spin_lock_irqsave(&irq->irq_lock,
> > > flags);
> > > +
> > > + /*
> > > + * We know that the interrupt is enabled
> > > and pending, so
> > > + * only check the priority.
> > > + */
> > > + if (irq->priority <= priority_mask)
> > > + has_pending = true;
> > > +
> > > + raw_spin_unlock_irqrestore(&irq-
> > > >irq_lock, flags);
> > > + vgic_put_irq(vcpu->kvm, irq);
> > > +
> > > + if (has_pending)
> > > + return true;
> > > + }
> > > + }
> > > +
> > > + return false;
> > > +}
> > > +
> > > /*
> > > * Detect any PPIs state changes, and propagate the state with
> > > KVM's
> > > * shadow structures.
> > > diff --git a/arch/arm64/kvm/vgic/vgic.c
> > > b/arch/arm64/kvm/vgic/vgic.c
> > > index e534876656ca7..5d18a03cc11d5 100644
> > > --- a/arch/arm64/kvm/vgic/vgic.c
> > > +++ b/arch/arm64/kvm/vgic/vgic.c
> > > @@ -1174,11 +1174,15 @@ int kvm_vgic_vcpu_pending_irq(struct
> > > kvm_vcpu *vcpu)
> > > unsigned long flags;
> > > struct vgic_vmcr vmcr;
> > >
> > > - if (!vcpu->kvm->arch.vgic.enabled)
> > > + if (!vcpu->kvm->arch.vgic.enabled && !vgic_is_v5(vcpu-
> > > >kvm))
> > > return false;
> > >
> > > - if (vcpu->arch.vgic_cpu.vgic_v3.its_vpe.pending_last)
> > > - return true;
> > > + if (vcpu->kvm->arch.vgic.vgic_model ==
> > > KVM_DEV_TYPE_ARM_VGIC_V5) {
> > > + return vgic_v5_has_pending_ppi(vcpu);
> > > + } else {
> > > + if (vcpu-
> > > >arch.vgic_cpu.vgic_v3.its_vpe.pending_last)
> > > + return true;
> > > + }
> > >
> > > vgic_get_vmcr(vcpu, &vmcr);
> > >
> > > diff --git a/arch/arm64/kvm/vgic/vgic.h
> > > b/arch/arm64/kvm/vgic/vgic.h
> > > index 5a77318ddb87a..4b3a1e7ca3fb4 100644
> > > --- a/arch/arm64/kvm/vgic/vgic.h
> > > +++ b/arch/arm64/kvm/vgic/vgic.h
> > > @@ -387,6 +387,7 @@ void vgic_debug_destroy(struct kvm *kvm);
> > > int vgic_v5_probe(const struct gic_kvm_info *info);
> > > void vgic_v5_set_ppi_ops(struct vgic_irq *irq);
> > > int vgic_v5_set_ppi_dvi(struct kvm_vcpu *vcpu, u32 irq, bool
> > > dvi);
> > > +bool vgic_v5_has_pending_ppi(struct kvm_vcpu *vcpu);
> > > void vgic_v5_flush_ppi_state(struct kvm_vcpu *vcpu);
> > > void vgic_v5_fold_irq_state(struct kvm_vcpu *vcpu);
> > > void vgic_v5_load(struct kvm_vcpu *vcpu);
> > > --
> > > 2.34.1
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