[PATCH v8 25/25] KVM: arm64: Add documentation for pKVM DMA isolation
From: Mostafa Saleh <smostafa@google.com>
Date: 2026-09-22 13:13:35
Also in:
kvmarm, linux-iommu, lkml
Subsystem:
documentation, kernel virtual machine (kvm), kernel virtual machine for arm64 (kvm/arm64), the rest · Maintainers:
Jonathan Corbet, Paolo Bonzini, Marc Zyngier, Oliver Upton, Linus Torvalds
Populate the section for DMA isolation in pKVM with the newly added KVM IOMMU and pKVM SMMUv3 driver details. Signed-off-by: Mostafa Saleh <smostafa@google.com> --- Documentation/virt/kvm/arm/pkvm.rst | 23 ++++++++++++++++++++++- 1 file changed, 22 insertions(+), 1 deletion(-)
diff --git a/Documentation/virt/kvm/arm/pkvm.rst b/Documentation/virt/kvm/arm/pkvm.rst
index 514992a79a83..ce67e2ae1f9a 100644
--- a/Documentation/virt/kvm/arm/pkvm.rst
+++ b/Documentation/virt/kvm/arm/pkvm.rst@@ -77,7 +77,28 @@ Status: **Unimplemented.** DMA isolation using an IOMMU ---------------------------- -Status: **Unimplemented.** +Status: Supported for devices behind SMMUv3 supporting dual stages +of translation. + +With ``CONFIG_ARM_SMMU_V3_PKVM``, the hypervisor will take over the SMMUs +on the system and provide an architectural emulation to the kernel SMMUv3 +driver. + +If some devices are not behind an IOMMU or behind another IOMMU architecture, +DMA isolation is not supported, as a driver must be provided for that. + +DMA isolation is enforced by dual stages of translation; similar to the CPU +where a driver can register their ops through ``kvm_iommu_register_driver`` +and implement ``host_stage2_idmap`` to shadow the CPU page table. + +The page tables for the stage-2 SMMUv3 will be allocated from a pool created +at boot with size configured from the command line "kvm-arm.iommu_pgt_mem" +The size must cover the worst case scenario for leaf mappings of system memory. + +This implementation trusts the system firmware not to allow the untrusted +host kernel to bypass the SMMUv3. +For example, by resetting the power. In that case, it is the firmware's +responsibility to save/restore the SMMUv3 state. Proxying of Trustzone services ------------------------------
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2.55.0.1082.g2b9226bbc0-goog