powerpc/8xx: Always fault when _PAGE_ACCESSED is not set

The kernel expects pte_young() to work regardless of CONFIG_SWAP.

Make sure a minor fault is taken to set _PAGE_ACCESSED when it
is not already set, regardless of the selection of CONFIG_SWAP.

This adds at least 3 instructions to the TLB miss exception
handlers fast path. Following patch will reduce this overhead.

Also update the rotation instruction to the correct number of bits
to reflect all changes done to _PAGE_ACCESSED over time.

Fixes: d069cb4 ("powerpc/8xx: Don't touch ACCESSED when no SWAP.")
Fixes: 5f35649 ("powerpc/8xx: remove unused _PAGE_WRITETHRU")
Fixes: e0a8e0d ("powerpc/8xx: Handle PAGE_USER via APG bits")
Fixes: 5b2753f ("powerpc/8xx: Implementation of PAGE_EXEC")
Fixes: a891c43 ("powerpc/8xx: Prepare handlers for _PAGE_HUGE for 512k pages.")
Cc: [email protected]
Signed-off-by: Christophe Leroy <[email protected]>
Signed-off-by: Michael Ellerman <[email protected]>
Link: https://lore.kernel.org/r/af834e8a0f1fa97bfae65664950f0984a70c4750.1602492856.git.christophe.leroy@csgroup.eu

Author: chleroy

arch/powerpc/kernel/head_8xx.S

@@ -202,9 +202,7 @@ SystemCall:
 
 InstructionTLBMiss:
 	mtspr	SPRN_SPRG_SCRATCH0, r10
-#if defined(ITLB_MISS_KERNEL) || defined(CONFIG_SWAP) || defined(CONFIG_HUGETLBFS)
 	mtspr	SPRN_SPRG_SCRATCH1, r11
-#endif
 
 	/* If we are faulting a kernel address, we have to use the
 	 * kernel page tables.
@@ -238,11 +236,9 @@ InstructionTLBMiss:
 	rlwimi	r11, r10, 32 - 9, _PMD_PAGE_512K
 	mtspr	SPRN_MI_TWC, r11
 #endif
-#ifdef CONFIG_SWAP
-	rlwinm	r11, r10, 32-5, _PAGE_PRESENT
+	rlwinm	r11, r10, 32-7, _PAGE_PRESENT
 	and	r11, r11, r10
 	rlwimi	r10, r11, 0, _PAGE_PRESENT
-#endif
 	/* The Linux PTE won't go exactly into the MMU TLB.
 	 * Software indicator bits 20 and 23 must be clear.
 	 * Software indicator bits 22, 24, 25, 26, and 27 must be
@@ -256,9 +252,7 @@ InstructionTLBMiss:
 
 	/* Restore registers */
 0:	mfspr	r10, SPRN_SPRG_SCRATCH0
-#if defined(ITLB_MISS_KERNEL) || defined(CONFIG_SWAP) || defined(CONFIG_HUGETLBFS)
 	mfspr	r11, SPRN_SPRG_SCRATCH1
-#endif
 	rfi
 	patch_site	0b, patch__itlbmiss_exit_1
 
@@ -268,9 +262,7 @@ InstructionTLBMiss:
 	addi	r10, r10, 1
 	stw	r10, (itlb_miss_counter - PAGE_OFFSET)@l(0)
 	mfspr	r10, SPRN_SPRG_SCRATCH0
-#if defined(ITLB_MISS_KERNEL) || defined(CONFIG_SWAP)
 	mfspr	r11, SPRN_SPRG_SCRATCH1
-#endif
 	rfi
 #endif
 
@@ -316,11 +308,9 @@ DataStoreTLBMiss:
 	 * r11 = ((r10 & PRESENT) & ((r10 & ACCESSED) >> 5));
 	 * r10 = (r10 & ~PRESENT) | r11;
 	 */
-#ifdef CONFIG_SWAP
-	rlwinm	r11, r10, 32-5, _PAGE_PRESENT
+	rlwinm	r11, r10, 32-7, _PAGE_PRESENT
 	and	r11, r11, r10
 	rlwimi	r10, r11, 0, _PAGE_PRESENT
-#endif
 	/* The Linux PTE won't go exactly into the MMU TLB.
 	 * Software indicator bits 24, 25, 26, and 27 must be
 	 * set.  All other Linux PTE bits control the behavior