LCU14 BURLINGAME

N. Bhat, P. Dixit, & C. Dall, LCU14

LCU14-110: Xen & ACPI: Status & Challenges

The Problem

ACPI on diverse ARM platforms is a non-trivial problem.

● Xen is minimal (no AML)● Xen needs to dynamically

hide certain devices in the hardware-provided ACPI block

● Xen needs to add new devices to ACPI

● Dom0 needs a modified ACPI blob - no iASL in Xen.

Xen Architecture with UEFI and ACPI

Hardware

Xen Hypervisor

VM 1DomU

Xen ArchitectureDom0

Xen PVDrivers

VM 2DomU

Xen PVDrivers

UEFIACPI

ACPI

Status - Tracked in CARD-1291

● Xen boots with ACPI on:● FVP Base model (UEFI)● Foundation Model (boot-wrapper with ACPI hack, memory in DT node)

● Support for● GIC● Timers● CPUs (SMP)● Memory (from UEFI)● UART

Status for humans

● _STA is a method implicitly defined for all resources in ACPI.● bit[0]: present, if set● bit[1]: enabled and decoding, if set● bit[2]: show in OSPM UI, if set● bit[3]: device functioning properly, if set● bit[4]: battery present, if set

● The _STA method is respected by Linux

_STA method status

● Proposal for Citrix/Linaro sponsored table

● Contains devices where the _STA method should be overridden

● Xen creates static STAO table

● Need to add Dom0 (Linux) support for STAO as RFC, experimental

STAO Table Status

● Has anything been reviewed?

● Action plan?

Upstream patch review status

Let’s get down to business

There are still a few unanswered questions left...

● Does Dom0 need access to runtime services?

● Do we run a separate instance of UEFI for Dom0?

Question #1

● Are we covering all devices needed by Xen?

● SMMU?

● PCIe?

Question #2

● Current STAO method only hides devices from the DSDT.

● Do we need to add new (modified) devices with AML?

Question #3

● Can we envision any devices described by AML that needs modifications?

● If so, any solution suggestions?

Question #4

● Do we need to copy the ACPI blob for Dom0 or just modify the hardware one and be done with it?

● Is rebooting Dom0 a case for copying it?

Question #5

● [Since this is an ongoing development, these slides may be expanded up until the day before the presentation with remaining development issues.]

Question #...

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