powerpc/mm/altmap: Fix altmap boundary check

[ Upstream commit 6722b25 ]

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: 9ef3463 ("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>

Author: kvaneesh

arch/powerpc/mm/init_64.c

@@ -314,8 +314,7 @@ void __ref vmemmap_free(unsigned long start, unsigned long end,
 	start = ALIGN_DOWN(start, page_size);
 	if (altmap) {
 		alt_start = altmap->base_pfn;
-		alt_end = altmap->base_pfn + altmap->reserve +
-			  altmap->free + altmap->alloc + altmap->align;
+		alt_end = altmap->base_pfn + altmap->reserve + altmap->free;
 	}
 
 	pr_debug("vmemmap_free %lx...%lx\n", start, end);