KVM: arm64: Handle aborts from protected VMs

KVM: arm64: Handle aborts from protected VMs

Introduce a new abort handler for resolving stage-2 page faults from
protected VMs by pinning and donating anonymous memory. This is
considerably simpler than the infamous user_mem_abort() as we only have
to deal with translation faults at the pte level.

Reviewed-by: Fuad Tabba <tabba@google.com>
Tested-by: Fuad Tabba <tabba@google.com>
Tested-by: Mostafa Saleh <smostafa@google.com>
Signed-off-by: Will Deacon <will@kernel.org>
Link: https://patch.msgid.link/20260330144841.26181-15-will@kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>