powerpc/mm/radix: Limit paca allocation in radix

On return from RTAS we access the paca variables and we have 64 bit
disabled. This requires us to limit paca in 32 bit range.

Fix this by setting ppc64_rma_size to first_memblock_size/1G range.
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/mm/pgtable-radix.c

@@ -351,7 +351,25 @@ void radix__early_init_mmu_secondary(void)
 void radix__setup_initial_memory_limit(phys_addr_t first_memblock_base,
 				phys_addr_t first_memblock_size)
 {
-	/* Finally limit subsequent allocations */
+	/* We don't currently support the first MEMBLOCK not mapping 0
+	 * physical on those processors
+	 */
+	BUG_ON(first_memblock_base != 0);
+	/*
+	 * We limit the allocation that depend on ppc64_rma_size
+	 * to first_memblock_size. We also clamp it to 1GB to
+	 * avoid some funky things such as RTAS bugs.
+	 *
+	 * On radix config we really don't have a limitation
+	 * on real mode access. But keeping it as above works
+	 * well enough.
+	 */
+	ppc64_rma_size = min_t(u64, first_memblock_size, 0x40000000);
+	/*
+	 * Finally limit subsequent allocations. We really don't want
+	 * to limit the memblock allocations to rma_size. FIXME!! should
+	 * we even limit at all ?
+	 */
 	memblock_set_current_limit(first_memblock_base + first_memblock_size);
 }