On 11/10/2024 15:14, Steven Price wrote:
On 08/10/2024 12:05, Jean-Philippe Brucker wrote:
On Fri, Oct 04, 2024 at 03:43:06PM +0100, Steven Price wrote:
Add some documentation on Arm CCA and the requirements for running Linux
as a Realm guest. Also update booting.rst to describe the requirement
for RIPAS RAM.
Signed-off-by: Steven Price <steven.price@xxxxxxx>
---
Documentation/arch/arm64/arm-cca.rst | 67 ++++++++++++++++++++++++++++
Documentation/arch/arm64/booting.rst | 3 ++
Documentation/arch/arm64/index.rst | 1 +
3 files changed, 71 insertions(+)
create mode 100644 Documentation/arch/arm64/arm-cca.rst
diff --git a/Documentation/arch/arm64/arm-cca.rst b/Documentation/arch/arm64/arm-cca.rst
new file mode 100644
index 000000000000..ab7f90e64c2f
--- /dev/null
+++ b/Documentation/arch/arm64/arm-cca.rst
@@ -0,0 +1,67 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+=====================================
+Arm Confidential Compute Architecture
+=====================================
+
+Arm systems that support the Realm Management Extension (RME) contain
+hardware to allow a VM guest to be run in a way which protects the code
+and data of the guest from the hypervisor. It extends the older "two
+world" model (Normal and Secure World) into four worlds: Normal, Secure,
+Root and Realm. Linux can then also be run as a guest to a monitor
+running in the Realm world.
+
+The monitor running in the Realm world is known as the Realm Management
+Monitor (RMM) and implements the Realm Management Monitor
+specification[1]. The monitor acts a bit like a hypervisor (e.g. it runs
+in EL2 and manages the stage 2 page tables etc of the guests running in
+Realm world), however much of the control is handled by a hypervisor
+running in the Normal World. The Normal World hypervisor uses the Realm
+Management Interface (RMI) defined by the RMM specification to request
+the RMM to perform operations (e.g. mapping memory or executing a vCPU).
+
+The RMM defines an environment for guests where the address space (IPA)
+is split into two. The lower half is protected - any memory that is
+mapped in this half cannot be seen by the Normal World and the RMM
+restricts what operations the Normal World can perform on this memory
+(e.g. the Normal World cannot replace pages in this region without the
+guest's cooperation). The upper half is shared, the Normal World is free
+to make changes to the pages in this region, and is able to emulate MMIO
+devices in this region too.
+
+A guest running in a Realm may also communicate with the RMM to request
+changes in its environment or to perform attestation about its
+environment. In particular it may request that areas of the protected
+address space are transitioned between 'RAM' and 'EMPTY' (in either
+direction). This allows a Realm guest to give up memory to be returned
+to the Normal World, or to request new memory from the Normal World.
+Without an explicit request from the Realm guest the RMM will otherwise
+prevent the Normal World from making these changes.
We could mention that this interface is "RSI", so readers know what to
look for next
Good idea.
+
+Linux as a Realm Guest
+----------------------
+
+To run Linux as a guest within a Realm, the following must be provided
+either by the VMM or by a `boot loader` run in the Realm before Linux:
+
+ * All protected RAM described to Linux (by DT or ACPI) must be marked
+ RIPAS RAM before handing over the Linux.
"handing control over to Linux", or something like that?
Indeed that actually makes grammatical sense! ;)
+
+ * MMIO devices must be either unprotected (e.g. emulated by the Normal
+ World) or marked RIPAS DEV.
+
+ * MMIO devices emulated by the Normal World and used very early in boot
+ (specifically earlycon) must be specified in the upper half of IPA.
+ For earlycon this can be done by specifying the address on the
+ command line, e.g.: ``earlycon=uart,mmio,0x101000000``
This is going to be needed frequently, so maybe we should explain in a
little more detail how we come up with this value: "e.g. with an IPA size
of 33 and the base address of the emulated UART at 0x1000000,
``earlycon=uart,mmio,0x101000000``"
(Because the example IPA size is rather unintuitive and specific to the
kvmtool memory map)
With the above addressed:
Reviewed-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
