powerpc/64s/hash: Disable subpage_prot syscall by default

The subpage_prot syscall was added for specialised system software
(Lx86) that has been discontinued for about 7 years, and is not thought
to be used elsewhere, so disable it by default.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200703011958.1166620-4-npiggin@gmail.com

arch/powerpc/Kconfig

@@ -833,13 +833,16 @@ config FORCE_MAX_ZONEORDER
 	  this in mind when choosing a value for this option.
 
 config PPC_SUBPAGE_PROT
-	bool "Support setting protections for 4k subpages"
+	bool "Support setting protections for 4k subpages (subpage_prot syscall)"
+	default n
 	depends on PPC_BOOK3S_64 && PPC_64K_PAGES
 	help
-	  This option adds support for a system call to allow user programs
+	  This option adds support for system call to allow user programs
 	  to set access permissions (read/write, readonly, or no access)
 	  on the 4k subpages of each 64k page.
 
+	  If unsure, say N here.
+
 config PPC_COPRO_BASE
 	bool
 

arch/powerpc/configs/powernv_defconfig

@@ -64,7 +64,6 @@ CONFIG_HWPOISON_INJECT=m
 CONFIG_TRANSPARENT_HUGEPAGE=y
 CONFIG_DEFERRED_STRUCT_PAGE_INIT=y
 CONFIG_PPC_64K_PAGES=y
-CONFIG_PPC_SUBPAGE_PROT=y
 CONFIG_SCHED_SMT=y
 CONFIG_PM=y
 CONFIG_HOTPLUG_PCI=y

arch/powerpc/configs/pseries_defconfig

@@ -57,7 +57,6 @@ CONFIG_MEMORY_HOTREMOVE=y
 CONFIG_KSM=y
 CONFIG_TRANSPARENT_HUGEPAGE=y
 CONFIG_PPC_64K_PAGES=y
-CONFIG_PPC_SUBPAGE_PROT=y
 CONFIG_SCHED_SMT=y
 CONFIG_HOTPLUG_PCI=y
 CONFIG_HOTPLUG_PCI_RPA=m