xen/arm: vgic-v3: Emulate correctly the re-distributor

xen/arm: vgic-v3: Emulate correctly the re-distributor

There is a one-to-one mapping between each re-distributors and processors.
Each re-distributors can be accessed by any processor at any time. For
instance during the initialization of the GIC, the drivers will browse
the re-distributor to find the one associated to the current processor
(via GICR_TYPER). So each re-distributor has its own MMIO region.

The current implementation of the vGICv3 emulation assumes that the
re-distributor region is banked. Therefore, the processor won't be able
to access other re-distributor. While this is working fine for Linux, a
processor will only access GICR_TYPER to find the associated re-distributor,
we have to implement correctly the re-distributor emulation in order to boot
other operating systems.

All emulated registers of the re-distributors take a vCPU in parameter
and necessary lock. Therefore concurrent access is already properly handled.

The missing bit is retrieving the right vCPU following the region accessed.
Retrieving the right vCPU could be slow, so it has been divided in 2 paths:
    - fast path: The current vCPU is accessing its own re-distributor
    - slow path: The current vCPU is accessing another re-distributor

As the processor needs to initialize itself, the former case is very
common. To handle the access quickly, the base address of the
re-distributor is computed and stored per-vCPU during the vCPU initialization.

The latter is less common and more complicate to handle. The re-distributors
can be spread across multiple regions in the memory.

During the domain creation, Xen will browse those regions to find the first
vCPU handled by this region.

When an access hits the slow path, Xen will:
    1) Retrieve the region using the base address of the re-distributor
    accessed
    2) Find the vCPU ID attached to the redistributor
    3) Check the validity of the vCPU. If it's not valid, a data abort
    will be injected to the guest

Finally, this patch also correctly support the bit GICR_TYPER.LAST which
indicates if the redistributor is the last one of the contiguous region.

Signed-off-by: Julien Grall <julien.grall@linaro.org>
Acked-by: Ian Campbell <ian.campbell@citrix.com>