FROMLIST: KVM: arm64: Allow attaching of non-coalescable pages to a hyp pool

All the contiguous pages used to initialize a 'struct hyp_pool' are
considered coalescable, which means that the hyp page allocator will
actively try to merge them with their buddies on the hyp_put_page() path.
However, using hyp_put_page() on a page that is not part of the inital
memory range given to a hyp_pool() is currently unsupported.

In order to allow dynamically extending hyp pools at run-time, add a
check to __hyp_attach_page() to allow inserting 'external' pages into
the free-list of order 0. This will be necessary to allow lazy donation
of pages from the host to the hypervisor when allocating guest stage-2
page-table pages at EL2.

Tested-by: Vincent Donnefort <vdonnefort@google.com>
Signed-off-by: Quentin Perret <qperret@google.com>
Signed-off-by: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20221020133827.5541-3-will@kernel.org


Signed-off-by: Will Deacon <willdeacon@google.com>
Bug: 233587962
Change-Id: Ie417f839ae6d30705847ab3e27e2b3c3ac6ee8dc
Signed-off-by: Quentin Perret <qperret@google.com>