[PATCH v9 06/25] KVM: arm64: iommu: Introduce IOMMU driver infrastructure
Mostafa Saleh
smostafa at google.com
Thu Oct 15 13:08:37 PDT 2026
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 at linaro.org>
Signed-off-by: Mostafa Saleh <smostafa at google.com>
---
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 at google.com>
+ */
+
+#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
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