powerpc/8xx: Map linear memory with huge pages

Map linear memory space with 512k and 8M pages whenever
possible.

Three mappings are performed:
- One for kernel text
- One for RO data
- One for the rest

Separating the mappings is done to be able to update the
protection later when using STRICT_KERNEL_RWX.

The ITLB miss handler now need to also handle huge TLBs
unless kernel text in pinned.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/c44f0ab5510474f25123d904cd1f4e5c6aa3c1ac.1589866984.git.christophe.leroy@csgroup.eu

arch/powerpc/kernel/head_8xx.S

@@ -224,7 +224,7 @@ InstructionTLBMiss:
 3:
 	mtcr	r11
 #endif
-#ifdef CONFIG_HUGETLBFS
+#if defined(CONFIG_HUGETLBFS) || !defined(CONFIG_PIN_TLB_TEXT)
 	lwz	r11, (swapper_pg_dir-PAGE_OFFSET)@l(r10)	/* Get level 1 entry */
 	mtspr	SPRN_MD_TWC, r11
 #else
@@ -234,7 +234,7 @@ InstructionTLBMiss:
 #endif
 	mfspr	r10, SPRN_MD_TWC
 	lwz	r10, 0(r10)	/* Get the pte */
-#ifdef CONFIG_HUGETLBFS
+#if defined(CONFIG_HUGETLBFS) || !defined(CONFIG_PIN_TLB_TEXT)
 	rlwimi	r11, r10, 32 - 9, _PMD_PAGE_512K
 	mtspr	SPRN_MI_TWC, r11
 #endif