FROMLIST: virt: gunyah: Add interfaces to map memory into guest address space

Gunyah virtual machines are created with either all memory provided at
VM creation using the Resource Manager memory parcel construct, or
Incrementally by enabling VM demand paging.

The Gunyah demand paging support is provided directly by the hypervisor
and does not require the creation of resource manager memory parcels.

Demand paging allows the host to map/unmap contiguous pages (folios) to
a Gunyah memory extent object with the correct rights allowing its
contained pages to be mapped into the Guest VM's address space. Memory
extents are Gunyah's mechanism for handling system memory abstracting
from the direct use of physical page numbers. Memory extents are
hypervisor objects and are therefore referenced and access controlled
with capabilities.

When a virtual machine is configured for demand paging, 3 memory
extent and 1 address space capabilities are provided to the host. The
resource manager defined policy is such that memory in the "host-only"
extent (the default) is private to the host. Memory in the "guest-only"
extent can be used for guest private mappings, and are unmapped from the
host. Memory in the "host-and-guest-shared" extent can be mapped
concurrently and shared between the host and guest VMs.

Implement two functions which Linux can use to move memory between the
virtual machines: gunyah_provide_folio and gunyah_reclaim_folio. Memory
that has been provided to the guest is tracked in a maple tree to be
reclaimed later. Folios provided to the virtual machine are assumed to
be owned Gunyah stack: the folio's ->private field is used for
bookkeeping about whether page is mapped into virtual machine.

Bug: 338347082
Link: https://lore.kernel.org/all/20240222-gunyah-v17-20-1e9da6763d38@quicinc.com/


Change-Id: I303fced6f7baef3c69540ef9fa9a7a04db957365
Signed-off-by: Elliot Berman <quic_eberman@quicinc.com>