KVM: arm64: nv: Track guest stage-2 mapping creation

During shadow stage-2 faults, in addition to creating mappings in the
shadow page tables, also allocate kvm_guest_s2_mapping objects, record
the mapping ranges, and insert them into the canonical and nested mmu's
guest_s2_mappings tree.

Note that because we allow parallel faulting, the interval trees could
store mappings that are not live in the shadow page tables. Storing a
superset of the live mappings is fine because we will only over-unmap
when we use this information later to do the targeted MMU notifier
unmap.

The mapping is also added to the interval trees if
kvm_pgtable_stage2_map() returns -EAGAIN. This is required for example,
when a 2M block map (A) races with a 4K page map (B):

1. (A) maps the 2M block in kvm_pgtable_visitor_cb()
2. (B) breaks that block into a table and maps 4K
3. (A) reloads and finds the table after kvm_pgtable_visitor_cb(),
   then descends into it.
4. (A) maps some 4K, but before it finishes it reads the entry mapped by
   (B).
5. (A) returns -EAGAIN although it had mapped a few pages.

In this case, we don't know what subrange is mapped, just track the
whole requested mapping range.

Signed-off-by: Wei-Lin Chang <weilin.chang@arm.com>
Reviewed-by: Oliver Upton <oupton@kernel.org>
Tested-by: Shuai Xue <xueshuai@linux.alibaba.com>
Tested-by: Itaru Kitayama <itaru.kitayama@fujitsu.com>
Link: https://patch.msgid.link/20260915154305.3852871-4-weilin.chang@arm.com
Signed-off-by: Marc Zyngier <maz@kernel.org>

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