[PATCH v6 13/39] KVM: arm64: gic-v5: Add emulation for ICC_IAFFIDR_EL1 accesses

Sascha Bischoff
2026-03-17T11:44:29Z

GICv5 doesn't provide an ICV_IAFFIDR_EL1 or ICH_IAFFIDR_EL2 for
providing the IAFFID to the guest. A guest access to the
ICC_IAFFIDR_EL1 must therefore be trapped and emulated to avoid the
guest accessing the host's ICC_IAFFIDR_EL1.

The virtual IAFFID is provided to the guest when it reads
ICC_IAFFIDR_EL1 (which always traps back to the hypervisor). Writes are
rightly ignored. KVM treats the GICv5 VPEID, the virtual IAFFID, and
the vcpu_id as the same, and so the vcpu_id is returned.

The trapping for the ICC_IAFFIDR_EL1 is always enabled when in a guest
context.

Co-authored-by: Timothy Hayes <timothy.hayes@arm.com>
Signed-off-by: Timothy Hayes <timothy.hayes@arm.com>
Signed-off-by: Sascha Bischoff <sascha.bischoff@arm.com>
---
arch/arm64/kvm/config.c | 10 +++++++++-
arch/arm64/kvm/sys_regs.c | 16 ++++++++++++++++
arch/arm64/kvm/vgic/vgic.h | 5 +++++
3 files changed, 30 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kvm/config.c b/arch/arm64/kvm/config.c
index e4ec1bda8dfcb..bac5f49fdbdef 100644
--- a/arch/arm64/kvm/config.c
+++ b/arch/arm64/kvm/config.c
@@ -1684,6 +1684,14 @@ static void __compute_hdfgwtr(struct kvm_vcpu *vcpu)
*vcpu_fgt(vcpu, HDFGWTR_EL2) |= HDFGWTR_EL2_MDSCR_EL1;
}

+static void __compute_ich_hfgrtr(struct kvm_vcpu *vcpu)
+{
+ __compute_fgt(vcpu, ICH_HFGRTR_EL2);
+
+ /* ICC_IAFFIDR_EL1 *always* needs to be trapped when running a guest */
+ *vcpu_fgt(vcpu, ICH_HFGRTR_EL2) &= ~ICH_HFGRTR_EL2_ICC_IAFFIDR_EL1;
+}
+
void kvm_vcpu_load_fgt(struct kvm_vcpu *vcpu)
{
if (!cpus_have_final_cap(ARM64_HAS_FGT))
@@ -1705,7 +1713,7 @@ void kvm_vcpu_load_fgt(struct kvm_vcpu *vcpu)
}

if (cpus_have_final_cap(ARM64_HAS_GICV5_CPUIF)) {
- __compute_fgt(vcpu, ICH_HFGRTR_EL2);
+ __compute_ich_hfgrtr(vcpu);
__compute_fgt(vcpu, ICH_HFGWTR_EL2);
__compute_fgt(vcpu, ICH_HFGITR_EL2);
}
diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index cd6deaf473159..d4531457ea026 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -681,6 +681,21 @@ static bool access_gic_dir(struct kvm_vcpu *vcpu,
return true;
}

+static bool access_gicv5_iaffid(struct kvm_vcpu *vcpu, struct sys_reg_params *p,
+ const struct sys_reg_desc *r)
+{
+ if (p->is_write)
+ return undef_access(vcpu, p, r);
+
+ /*
+ * For GICv5 VMs, the IAFFID value is the same as the VPE ID. The VPE ID
+ * is the same as the VCPU's ID.
+ */
+ p->regval = FIELD_PREP(ICC_IAFFIDR_EL1_IAFFID, vcpu->vcpu_id);
+
+ return true;
+}
+
static bool trap_raz_wi(struct kvm_vcpu *vcpu,
struct sys_reg_params *p,
const struct sys_reg_desc *r)
@@ -3405,6 +3420,7 @@ static const struct sys_reg_desc sys_reg_descs[] = {
{ SYS_DESC(SYS_ICC_AP1R1_EL1), undef_access },
{ SYS_DESC(SYS_ICC_AP1R2_EL1), undef_access },
{ SYS_DESC(SYS_ICC_AP1R3_EL1), undef_access },
+ { SYS_DESC(SYS_ICC_IAFFIDR_EL1), access_gicv5_iaffid },
{ SYS_DESC(SYS_ICC_DIR_EL1), access_gic_dir },
{ SYS_DESC(SYS_ICC_RPR_EL1), undef_access },
{ SYS_DESC(SYS_ICC_SGI1R_EL1), access_gic_sgi },
diff --git a/arch/arm64/kvm/vgic/vgic.h b/arch/arm64/kvm/vgic/vgic.h
index f2924f8211974..7b7eed69d7973 100644
--- a/arch/arm64/kvm/vgic/vgic.h
+++ b/arch/arm64/kvm/vgic/vgic.h
@@ -447,6 +447,11 @@ static inline bool kvm_has_gicv3(struct kvm *kvm)
return kvm_has_feat(kvm, ID_AA64PFR0_EL1, GIC, IMP);
}

+static inline bool kvm_has_gicv5(struct kvm *kvm)
+{
+ return kvm_has_feat(kvm, ID_AA64PFR2_EL1, GCIE, IMP);
+}
+
void vgic_v3_flush_nested(struct kvm_vcpu *vcpu);
void vgic_v3_sync_nested(struct kvm_vcpu *vcpu);
void vgic_v3_load_nested(struct kvm_vcpu *vcpu);
--
2.34.1