powerpc/book3e: Activate KUEP at all time

On book3e,
- When using 64 bits PTE: User pages don't have the SX bit defined
so KUEP is always active.
- When using 32 bits PTE: Implement KUEP by clearing SX bit during
TLB miss for user pages. The impact is minimal and worth neither
boot time nor build time selection.

Activate it at all time.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/e376b114283fb94504e2aa2de846780063252cde.1634627931.git.christophe.leroy@csgroup.eu

arch/powerpc/kernel/head_fsl_booke.S

@@ -777,6 +777,7 @@ END_MMU_FTR_SECTION_IFSET(MMU_FTR_BIG_PHYS)
 	andi.	r10, r11, _PAGE_USER	/* Test for _PAGE_USER */
 	slwi	r10, r12, 1
 	or	r10, r10, r12
+	rlwinm	r10, r10, 0, ~_PAGE_EXEC	/* Clear SX on user pages */
 	iseleq	r12, r12, r10
 	rlwimi	r13, r12, 0, 20, 31	/* Get RPN from PTE, merge w/ perms */
 	mtspr	SPRN_MAS3, r13

arch/powerpc/platforms/Kconfig.cputype

@@ -299,6 +299,8 @@ config PPC_FSL_BOOK3E
 	select FSL_EMB_PERFMON
 	select PPC_SMP_MUXED_IPI
 	select PPC_DOORBELL
+	select PPC_HAVE_KUEP
+	select PPC_KUEP
 	default y if FSL_BOOKE
 
 config PTE_64BIT