powerpc: simplify BDI switch

There is no reason to re-read each time the pointer at
location 0xf0 as it is fixed and known.
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/mmu.h

@@ -356,6 +356,8 @@ extern void early_init_mmu_secondary(void);
 extern void setup_initial_memory_limit(phys_addr_t first_memblock_base,
 				       phys_addr_t first_memblock_size);
 static inline void mmu_early_init_devtree(void) { }
+
+extern void *abatron_pteptrs[2];
 #endif /* __ASSEMBLY__ */
 #endif
 

arch/powerpc/kernel/head_32.S

@@ -1027,9 +1027,8 @@ _ENTRY(switch_mmu_context)
 	 * The PGDIR is passed as second argument.
 	 */
 	lwz	r4,MM_PGD(r4)
-	lis	r5, KERNELBASE@h
-	lwz	r5, 0xf0(r5)
-	stw	r4, 0x4(r5)
+	lis	r5, abatron_pteptrs@ha
+	stw	r4, abatron_pteptrs@l + 0x4(r5)
 #endif
 	li	r4,0
 	isync

arch/powerpc/kernel/head_40x.S

@@ -953,9 +953,8 @@ _GLOBAL(set_context)
 	/* Context switch the PTE pointer for the Abatron BDI2000.
 	 * The PGDIR is the second parameter.
 	 */
-	lis	r5, KERNELBASE@h
-	lwz	r5, 0xf0(r5)
-	stw	r4, 0x4(r5)
+	lis	r5, abatron_pteptrs@ha
+	stw	r4, abatron_pteptrs@l + 0x4(r5)
 #endif
 	sync
 	mtspr	SPRN_PID,r3

arch/powerpc/kernel/head_8xx.S

@@ -989,5 +989,6 @@ swapper_pg_dir:
 /* Room for two PTE table poiners, usually the kernel and current user
  * pointer to their respective root page table (pgdir).
  */
+	.globl	abatron_pteptrs
 abatron_pteptrs:
 	.space	8

arch/powerpc/mm/8xx_mmu.c

@@ -162,14 +162,11 @@ void set_context(unsigned long id, pgd_t *pgd)
 {
 	s16 offset = (s16)(__pa(swapper_pg_dir));
 
-#ifdef CONFIG_BDI_SWITCH
-	pgd_t	**ptr = *(pgd_t ***)(KERNELBASE + 0xf0);
-
 	/* Context switch the PTE pointer for the Abatron BDI2000.
 	 * The PGDIR is passed as second argument.
 	 */
-	*(ptr + 1) = pgd;
-#endif
+	if (IS_ENABLED(CONFIG_BDI_SWITCH))
+		abatron_pteptrs[1] = pgd;
 
 	/* Register M_TWB will contain base address of level 1 table minus the
 	 * lower part of the kernel PGDIR base address, so that all accesses to