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) Agreed. Thanks, Steve > Thanks, > Jean > >> + >> + * Linux will use bounce buffers for communicating with unprotected >> + devices. It will transition some protected memory to RIPAS EMPTY and >> + expect to be able to access unprotected pages at the same IPA address >> + but with the highest valid IPA bit set. The expectation is that the >> + VMM will remove the physical pages from the protected mapping and >> + provide those pages as unprotected pages. >> + >> +References >> +---------- >> +[1] https://developer.arm.com/documentation/den0137/ >> diff --git a/Documentation/arch/arm64/booting.rst b/Documentation/arch/arm64/booting.rst >> index b57776a68f15..30164fb24a24 100644 >> --- a/Documentation/arch/arm64/booting.rst >> +++ b/Documentation/arch/arm64/booting.rst >> @@ -41,6 +41,9 @@ to automatically locate and size all RAM, or it may use knowledge of >> the RAM in the machine, or any other method the boot loader designer >> sees fit.) >> >> +For Arm Confidential Compute Realms this includes ensuring that all >> +protected RAM has a Realm IPA state (RIPAS) of "RAM". >> + >> >> 2. Setup the device tree >> ------------------------- >> diff --git a/Documentation/arch/arm64/index.rst b/Documentation/arch/arm64/index.rst >> index 78544de0a8a9..12c243c3af20 100644 >> --- a/Documentation/arch/arm64/index.rst >> +++ b/Documentation/arch/arm64/index.rst >> @@ -10,6 +10,7 @@ ARM64 Architecture >> acpi_object_usage >> amu >> arm-acpi >> + arm-cca >> asymmetric-32bit >> booting >> cpu-feature-registers >> -- >> 2.34.1 >> >>
