1 files changed, 50 insertions, 1 deletions

diff --git a/arch/powerpc/mm/init_64.c b/arch/powerpc/mm/init_64.c
index 8ed035d2edb5..e3734edffa69 100644
--- a/arch/powerpc/mm/init_64.c
+++ b/arch/powerpc/mm/init_64.c
@@ -304,5 +304,54 @@ void register_page_bootmem_memmap(unsigned long section_nr,
                                   struct page *start_page, unsigned long size)
 {
 }
-#endif /* CONFIG_SPARSEMEM_VMEMMAP */
 
+/*
+ * We do not have access to the sparsemem vmemmap, so we fallback to
+ * walking the list of sparsemem blocks which we already maintain for
+ * the sake of crashdump. In the long run, we might want to maintain
+ * a tree if performance of that linear walk becomes a problem.
+ *
+ * realmode_pfn_to_page functions can fail due to:
+ * 1) As real sparsemem blocks do not lay in RAM continously (they
+ * are in virtual address space which is not available in the real mode),
+ * the requested page struct can be split between blocks so get_page/put_page
+ * may fail.
+ * 2) When huge pages are used, the get_page/put_page API will fail
+ * in real mode as the linked addresses in the page struct are virtual
+ * too.
+ */
+struct page *realmode_pfn_to_page(unsigned long pfn)
+{
+        struct vmemmap_backing *vmem_back;
+        struct page *page;
+        unsigned long page_size = 1 << mmu_psize_defs[mmu_vmemmap_psize].shift;
+        unsigned long pg_va = (unsigned long) pfn_to_page(pfn);
+
+        for (vmem_back = vmemmap_list; vmem_back; vmem_back = vmem_back->list) {
+                if (pg_va < vmem_back->virt_addr)
+                        continue;
+
+                /* Check that page struct is not split between real pages */
+                if ((pg_va + sizeof(struct page)) >
+                                (vmem_back->virt_addr + page_size))
+                        return NULL;
+
+                page = (struct page *) (vmem_back->phys + pg_va -
+                                vmem_back->virt_addr);
+                return page;
+        }
+
+        return NULL;
+}
+EXPORT_SYMBOL_GPL(realmode_pfn_to_page);
+
+#elif defined(CONFIG_FLATMEM)
+
+struct page *realmode_pfn_to_page(unsigned long pfn)
+{
+        struct page *page = pfn_to_page(pfn);
+        return page;
+}
+EXPORT_SYMBOL_GPL(realmode_pfn_to_page);
+
+#endif /* CONFIG_SPARSEMEM_VMEMMAP/CONFIG_FLATMEM */