Document the hypercalls user for the MMIO guard infrastructure.
Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>
---
Documentation/virt/kvm/arm/index.rst | 1 +
Documentation/virt/kvm/arm/mmio-guard.rst | 74 +++++++++++++++++++++++
2 files changed, 75 insertions(+)
create mode 100644 Documentation/virt/kvm/arm/mmio-guard.rst
diff --git a/Documentation/virt/kvm/arm/index.rst b/Documentation/virt/kvm/arm/index.rst
index 78a9b670aafe..e77a0ee2e2d4 100644
--- a/Documentation/virt/kvm/arm/index.rst
+++ b/Documentation/virt/kvm/arm/index.rst
@@ -11,3 +11,4 @@ ARM
psci
pvtime
ptp_kvm
+ mmio-guard
diff --git a/Documentation/virt/kvm/arm/mmio-guard.rst b/Documentation/virt/kvm/arm/mmio-guard.rst
new file mode 100644
index 000000000000..8b3c852c5d92
--- /dev/null
+++ b/Documentation/virt/kvm/arm/mmio-guard.rst
@@ -0,0 +1,74 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+==============
+KVM MMIO guard
+==============
+
+KVM implements device emulation by handling translation faults to any
+IPA range that is not contained in a memory slot. Such a translation
+fault is in most cases passed on to userspace (or in rare cases to the
+host kernel) with the address, size and possibly data of the access
+for emulation.
+
+Should the guest exit with an address that is not one that corresponds
+to an emulatable device, userspace may take measures that are not the
+most graceful as far as the guest is concerned (such as terminating it
+or delivering a fatal exception).
+
+There is also an element of trust: by forwarding the request to
+userspace, the kernel assumes that the guest trusts userspace to do
+the right thing.
+
+The KVM MMIO guard offers a way to mitigate this last point: a guest
+can request that only certain regions of the IPA space are valid as
+MMIO. Only these regions will be handled as an MMIO, and any other
+will result in an exception being delivered to the guest.
+
+This relies on a set of hypercalls defined in the KVM-specific range,
+using the HVC64 calling convention.
+
+* ARM_SMCCC_KVM_FUNC_MMIO_GUARD_INFO
+
+ ============== ======== ================================
+ Function ID: (uint32) 0xC6000002
+ Arguments: none
+ Return Values: (int64) NOT_SUPPORTED(-1) on error, or
+ (uint64) Protection Granule (PG) size in
+ bytes (r0)
+ ============== ======== ================================
+
+* ARM_SMCCC_KVM_FUNC_MMIO_GUARD_ENROLL
+
+ ============== ======== ==============================
+ Function ID: (uint32) 0xC6000003
+ Arguments: none
+ Return Values: (int64) NOT_SUPPORTED(-1) on error, or
+ RET_SUCCESS(0) (r0)
+ ============== ======== ==============================
+
+* ARM_SMCCC_KVM_FUNC_MMIO_GUARD_MAP
+
+ ============== ======== ====================================
+ Function ID: (uint32) 0xC6000004
+ Arguments: (uint64) The base of the PG-sized IPA range
+ that is allowed to be accessed as
+ MMIO. Must be aligned to the PG size
+ (r1)
+ (uint64) Index in the MAIR_EL1 register
+ providing the memory attribute that
+ is used by the guest (r2)
+ Return Values: (int64) NOT_SUPPORTED(-1) on error, or
+ RET_SUCCESS(0) (r0)
+ ============== ======== ====================================
+
+* ARM_SMCCC_KVM_FUNC_MMIO_GUARD_UNMAP
+
+ ============== ======== ======================================
+ Function ID: (uint32) 0xC6000005
+ Arguments: (uint64) PG-sized IPA range aligned to the PG
+ size which has been previously mapped.
+ Must be aligned to the PG size and
+ have been previously mapped (r1)
+ Return Values: (int64) NOT_SUPPORTED(-1) on error, or
+ RET_SUCCESS(0) (r0)
+ ============== ======== ======================================
--
2.30.2
