powerpc/mm/altmap: Fix altmap boundary check

stable inclusion
from stable-v5.10.190
commit fbb6657037d4d396a320b945e14c5db721bc1c3a
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I928UI

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=fbb6657037d4d396a320b945e14c5db721bc1c3a



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[ Upstream commit 6722b257 ]

altmap->free includes the entire free space from which altmap blocks
can be allocated. So when checking whether the kernel is doing altmap
block free, compute the boundary correctly, otherwise memory hotunplug
can fail.

Fixes: 9ef34630 ("powerpc/mm: Fallback to RAM if the altmap is unusable")
Signed-off-by: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230724181320.471386-1-aneesh.kumar@linux.ibm.com


Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: sanglipeng <sanglipeng1@jd.com>