[PATCH v9 06/25] KVM: arm64: iommu: Introduce IOMMU driver infrastructure
From: Mostafa Saleh
Date: Thu Oct 15 2026 - 16:10:43 EST
To establish DMA isolation, pKVM needs an IOMMU driver that provides
ops implemented at EL2.
Only one driver can be used. It is registered before KVM initialises
with pkvm_iommu_register_driver().
Registration must come from an initcall between core_initcall() and
fs_initcall(): earlier and the CPU capabilities are not finalised,
later and kvm_arm_init() at device_initcall level has already consumed
the ops.
The hypervisor calls the driver's init last in __pkvm_init_finalise(),
so that no step that can fail runs after it, as drivers have no
teardown. DMA isolation stays optional: without a registered driver
pKVM initialises as before.
Signed-off-by: Jean-Philippe Brucker <jean-philippe@xxxxxxxxxx>
Signed-off-by: Mostafa Saleh <smostafa@xxxxxxxxxx>
---
arch/arm64/include/asm/kvm_host.h | 7 +++++
arch/arm64/kvm/Makefile | 2 +-
arch/arm64/kvm/hyp/include/nvhe/iommu.h | 13 +++++++++
arch/arm64/kvm/hyp/nvhe/Makefile | 3 ++-
arch/arm64/kvm/hyp/nvhe/iommu.c | 19 ++++++++++++++
arch/arm64/kvm/hyp/nvhe/setup.c | 10 +++++++
arch/arm64/kvm/iommu.c | 35 +++++++++++++++++++++++++
7 files changed, 87 insertions(+), 2 deletions(-)
create mode 100644 arch/arm64/kvm/hyp/include/nvhe/iommu.h
create mode 100644 arch/arm64/kvm/hyp/nvhe/iommu.c
create mode 100644 arch/arm64/kvm/iommu.c
diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index cd9b9d2462f9..0c7fb6fa24f5 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -1717,4 +1717,11 @@ static __always_inline enum fgt_group_id __fgt_reg_to_group_id(enum vcpu_sysreg
long kvm_get_cap_for_kvm_ioctl(unsigned int ioctl, long *ext);
+struct pkvm_iommu_ops;
+extern struct pkvm_iommu_ops *kvm_nvhe_sym(pkvm_iommu_ops);
+
+#ifndef __KVM_NVHE_HYPERVISOR__
+int __init pkvm_iommu_register_driver(struct pkvm_iommu_ops *hyp_ops);
+#endif
+
#endif /* __ARM64_KVM_HOST_H__ */
diff --git a/arch/arm64/kvm/Makefile b/arch/arm64/kvm/Makefile
index 59612d2f277c..0ddef54f7434 100644
--- a/arch/arm64/kvm/Makefile
+++ b/arch/arm64/kvm/Makefile
@@ -24,7 +24,7 @@ kvm-y += arm.o mmu.o mmio.o psci.o hypercalls.o pvtime.o \
vgic/vgic-mmio.o vgic/vgic-mmio-v2.o \
vgic/vgic-mmio-v3.o vgic/vgic-kvm-device.o \
vgic/vgic-its.o vgic/vgic-debug.o vgic/vgic-v3-nested.o \
- vgic/vgic-v5.o
+ vgic/vgic-v5.o iommu.o
kvm-$(CONFIG_HW_PERF_EVENTS) += pmu-emul.o pmu.o
kvm-$(CONFIG_ARM64_PTR_AUTH) += pauth.o
diff --git a/arch/arm64/kvm/hyp/include/nvhe/iommu.h b/arch/arm64/kvm/hyp/include/nvhe/iommu.h
new file mode 100644
index 000000000000..df3d0cc5d4db
--- /dev/null
+++ b/arch/arm64/kvm/hyp/include/nvhe/iommu.h
@@ -0,0 +1,13 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ARM64_KVM_NVHE_IOMMU_H__
+#define __ARM64_KVM_NVHE_IOMMU_H__
+
+#include <asm/kvm_host.h>
+
+struct pkvm_iommu_ops {
+ int (*init)(void);
+};
+
+int pkvm_iommu_init(void);
+
+#endif /* __ARM64_KVM_NVHE_IOMMU_H__ */
diff --git a/arch/arm64/kvm/hyp/nvhe/Makefile b/arch/arm64/kvm/hyp/nvhe/Makefile
index f57450ebcb49..7cb79db9bc47 100644
--- a/arch/arm64/kvm/hyp/nvhe/Makefile
+++ b/arch/arm64/kvm/hyp/nvhe/Makefile
@@ -24,7 +24,8 @@ CFLAGS_switch.nvhe.o += -Wno-override-init
hyp-obj-y := timer-sr.o sysreg-sr.o debug-sr.o switch.o tlb.o hyp-init.o host.o \
hyp-main.o hyp-smp.o psci-relay.o early_alloc.o page_alloc.o \
- cache.o setup.o mm.o mem_protect.o sys_regs.o pkvm.o stacktrace.o ffa.o
+ cache.o setup.o mm.o mem_protect.o sys_regs.o pkvm.o stacktrace.o ffa.o \
+ iommu.o
hyp-obj-y += ../vgic-v3-sr.o ../aarch32.o ../vgic-v2-cpuif-proxy.o ../entry.o \
../hyp-entry.o ../exception.o ../pgtable.o ../vgic-v5-sr.o
hyp-obj-y += ../../../kernel/smccc-call.o
diff --git a/arch/arm64/kvm/hyp/nvhe/iommu.c b/arch/arm64/kvm/hyp/nvhe/iommu.c
new file mode 100644
index 000000000000..f4572b2dba76
--- /dev/null
+++ b/arch/arm64/kvm/hyp/nvhe/iommu.c
@@ -0,0 +1,19 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * IOMMU operations for pKVM
+ *
+ * Copyright (C) 2022 Linaro Ltd.
+ */
+#include <nvhe/iommu.h>
+
+/* Only one set of ops supported */
+struct pkvm_iommu_ops *pkvm_iommu_ops __ro_after_init;
+
+int pkvm_iommu_init(void)
+{
+ /* Keep DMA isolation optional. */
+ if (!pkvm_iommu_ops || !pkvm_iommu_ops->init)
+ return 0;
+
+ return pkvm_iommu_ops->init();
+}
diff --git a/arch/arm64/kvm/hyp/nvhe/setup.c b/arch/arm64/kvm/hyp/nvhe/setup.c
index 45ac5f2ba4f7..620b05c2799a 100644
--- a/arch/arm64/kvm/hyp/nvhe/setup.c
+++ b/arch/arm64/kvm/hyp/nvhe/setup.c
@@ -13,6 +13,7 @@
#include <nvhe/early_alloc.h>
#include <nvhe/ffa.h>
#include <nvhe/gfp.h>
+#include <nvhe/iommu.h>
#include <nvhe/memory.h>
#include <nvhe/mem_protect.h>
#include <nvhe/mm.h>
@@ -342,6 +343,15 @@ void __noreturn __pkvm_init_finalise(void)
if (ret)
goto out;
+ /*
+ * IOMMU init is done at the end, as it sets up and initializes many
+ * resources that would be leaked if the hypervisor fails after as there
+ * is no remove_iommu_driver() at the moment.
+ */
+ ret = pkvm_iommu_init();
+ if (ret)
+ goto out;
+
pkvm_hyp_vm_table_init(vm_table_base);
pkvm_ownership_selftest(selftest_base);
diff --git a/arch/arm64/kvm/iommu.c b/arch/arm64/kvm/iommu.c
new file mode 100644
index 000000000000..ab3f37d61579
--- /dev/null
+++ b/arch/arm64/kvm/iommu.c
@@ -0,0 +1,35 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2025 Google LLC
+ * Author: Mostafa Saleh <smostafa@xxxxxxxxxx>
+ */
+
+#include <linux/kvm_host.h>
+
+#include <asm/kvm_mmu.h>
+
+static DEFINE_MUTEX(pkvm_iommu_reg_lock);
+
+/**
+ * pkvm_iommu_register_driver() - Register the hypervisor IOMMU driver
+ * @hyp_ops: Kernel address of the ops, which live in the hypervisor image,
+ * i.e. &kvm_nvhe_sym(ops).
+ *
+ * Only one driver can be registered. Call from an initcall between
+ * core_initcall() and fs_initcall().
+ *
+ * Return: 0 on success.
+ */
+int __init pkvm_iommu_register_driver(struct pkvm_iommu_ops *hyp_ops)
+{
+ guard(mutex)(&pkvm_iommu_reg_lock);
+
+ if (!is_protected_kvm_enabled() || is_kvm_arm_initialised())
+ return -EPERM;
+
+ if (kvm_nvhe_sym(pkvm_iommu_ops))
+ return -EBUSY;
+
+ kvm_nvhe_sym(pkvm_iommu_ops) = kern_hyp_va(kvm_ksym_ref(hyp_ops));
+ return 0;
+}
--
2.56.0.176.g3575e65682-goog