powerpc/mm: Dump linux pagetables

Useful to be able to dump the kernels page tables to check permissions
and memory types - derived from arm64's implementation.

Add a debugfs file to check the page tables. To use this the PPC_PTDUMP
config option must be selected.
Signed-off-by: Rashmica Gupta <rashmicy@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/Kconfig.debug

@@ -354,4 +354,16 @@ config FAIL_IOMMU
 
 	  If you are unsure, say N.
 
+config PPC_PTDUMP
+        bool "Export kernel pagetable layout to userspace via debugfs"
+        depends on DEBUG_KERNEL
+        select DEBUG_FS
+        help
+	  This option exports the state of the kernel pagetables to a
+	  debugfs file. This is only useful for kernel developers who are
+	  working in architecture specific areas of the kernel - probably
+	  not a good idea to enable this feature in a production kernel.
+
+	  If you are unsure, say N.
+
 endmenu

arch/powerpc/mm/Makefile

@@ -42,3 +42,4 @@ obj-$(CONFIG_NOT_COHERENT_CACHE) += dma-noncoherent.o
 obj-$(CONFIG_HIGHMEM)		+= highmem.o
 obj-$(CONFIG_PPC_COPRO_BASE)	+= copro_fault.o
 obj-$(CONFIG_SPAPR_TCE_IOMMU)	+= mmu_context_iommu.o
+obj-$(CONFIG_PPC_PTDUMP)	+= dump_linuxpagetables.o