spapr: nested: Add support for reporting Hostwide state counter

spapr: nested: Add support for reporting Hostwide state counter

Add support for reporting Hostwide state counters for nested KVM pseries
guests running with 'cap-nested-papr' on Qemu-TCG acting as
L0-hypervisor. The Hostwide state counters are statistics about state that
L0-hypervisor maintains for the L2-guests and represent the state of all
L2-guests, not just a specific one.

These stats counters are exposed to L1-Hypervisor by the L0-Hypervisor via a
new bit-flag named 'getHostWideState' for the H_GUEST_GET_STATE hcall which
is documented at [1]. Once this flag is set the hcall should populate the
Guest-State-Elements in the requested GSB with the stat counter
values. Currently following five counters are supported:

* l0_guest_heap_size_inuse
* l0_guest_heap_size_max
* l0_guest_pagetable_size_inuse
* l0_guest_pagetable_size_max
* l0_guest_pagetable_reclaimed

At the moment '0' is being reported for all these counters as these
counters doesn't align with how L0-Qemu manages Guest memory.

The patch implements support for these counters by adding new members to
the 'struct SpaprMachineStateNested'. These new members are then plugged
into the existing 'guest_state_element_types[]' with the help of a new
macro 'GSBE_NESTED_MACHINE_DW' together with a new helper
'get_machine_ptr()'. guest_state_request_check() is updated to ensure
correctness of the requested GSB and finally h_guest_getset_state() is
updated to handle the newly introduced flag
'GUEST_STATE_REQUEST_HOST_WIDE'.

This patch is tested with the proposed linux-kernel implementation to
expose these stat-counter as perf-events at [2].

[1]
https://lore.kernel.org/all/20241222140247.174998-2-vaibhav@linux.ibm.com

[2]
https://lore.kernel.org/all/20241222140247.174998-1-vaibhav@linux.ibm.com

Signed-off-by: Vaibhav Jain <vaibhav@linux.ibm.com>
Reviewed-by: Harsh Prateek Bora <harshpb@linux.ibm.com>
Message-ID: <20250221155449.530645-1-vaibhav@linux.ibm.com>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>