[PATCH v5 09/36] KVM: arm64: gic-v5: Detect implemented PPIs on boot

Sascha Bischoff
2026-02-26T15:58:55Z

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@arm.com>
Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
---
arch/arm64/kvm/vgic/vgic-v5.c | 30 ++++++++++++++++++++++++++++++
include/kvm/arm_vgic.h | 5 +++++
include/linux/irqchip/arm-gic-v5.h | 10 ++++++++++
3 files changed, 45 insertions(+)

diff --git a/arch/arm64/kvm/vgic/vgic-v5.c b/arch/arm64/kvm/vgic/vgic-v5.c
index 9d9aa5774e634..2c51b9ba4f118 100644
--- a/arch/arm64/kvm/vgic/vgic-v5.c
+++ b/arch/arm64/kvm/vgic/vgic-v5.c
@@ -8,6 +8,34 @@

#include "vgic.h"

+static struct vgic_v5_ppi_caps ppi_caps;
+
+/*
+ * Not all PPIs are guaranteed to be implemented for GICv5. Deterermine which
+ * ones are, and generate a mask.
+ */
+static void vgic_v5_get_implemented_ppis(void)
+{
+ if (!cpus_have_final_cap(ARM64_HAS_GICV5_CPUIF))
+ return;
+
+ /*
+ * If we have KVM, we have EL2, which means that we have support for the
+ * EL1 and EL2 P & V timers.
+ */
+ ppi_caps.impl_ppi_mask[0] |= BIT_ULL(GICV5_ARCH_PPI_CNTHP);
+ ppi_caps.impl_ppi_mask[0] |= BIT_ULL(GICV5_ARCH_PPI_CNTV);
+ ppi_caps.impl_ppi_mask[0] |= BIT_ULL(GICV5_ARCH_PPI_CNTHV);
+ ppi_caps.impl_ppi_mask[0] |= BIT_ULL(GICV5_ARCH_PPI_CNTP);
+
+ /* The SW_PPI should be available */
+ ppi_caps.impl_ppi_mask[0] |= BIT_ULL(GICV5_ARCH_PPI_SW_PPI);
+
+ /* The PMUIRQ is available if we have the PMU */
+ if (system_supports_pmuv3())
+ ppi_caps.impl_ppi_mask[0] |= BIT_ULL(GICV5_ARCH_PPI_PMUIRQ);
+}
+
/*
* Probe for a vGICv5 compatible interrupt controller, returning 0 on success.
* Currently only supports GICv3-based VMs on a GICv5 host, and hence only
@@ -18,6 +46,8 @@ int vgic_v5_probe(const struct gic_kvm_info *info)
u64 ich_vtr_el2;
int ret;

+ vgic_v5_get_implemented_ppis();
+
if (!cpus_have_final_cap(ARM64_HAS_GICV5_LEGACY))
return -ENODEV;

diff --git a/include/kvm/arm_vgic.h b/include/kvm/arm_vgic.h
index f12b47e589abc..9e4798333b46c 100644
--- a/include/kvm/arm_vgic.h
+++ b/include/kvm/arm_vgic.h
@@ -410,6 +410,11 @@ struct vgic_v3_cpu_if {
unsigned int used_lrs;
};

+/* What PPI capabilities does a GICv5 host have */
+struct vgic_v5_ppi_caps {
+ u64 impl_ppi_mask[2];
+};
+
struct vgic_cpu {
/* CPU vif control registers for world switch */
union {
diff --git a/include/linux/irqchip/arm-gic-v5.h b/include/linux/irqchip/arm-gic-v5.h
index b78488df6c989..1dc05afcab53e 100644
--- a/include/linux/irqchip/arm-gic-v5.h
+++ b/include/linux/irqchip/arm-gic-v5.h
@@ -24,6 +24,16 @@
#define GICV5_HWIRQ_TYPE_LPI UL(0x2)
#define GICV5_HWIRQ_TYPE_SPI UL(0x3)

+/*
+ * Architected PPIs
+ */
+#define GICV5_ARCH_PPI_SW_PPI 0x3
+#define GICV5_ARCH_PPI_PMUIRQ 0x17
+#define GICV5_ARCH_PPI_CNTHP 0x1a
+#define GICV5_ARCH_PPI_CNTV 0x1b
+#define GICV5_ARCH_PPI_CNTHV 0x1c
+#define GICV5_ARCH_PPI_CNTP 0x1e
+
/*
* Tables attributes
*/
--
2.34.1