powerpc/6xx: Store PGDIR physical address in a SPRG

Use SPRN_SPRG2 to store the current thread PGDIR and
avoid reading thread_struct.pgdir at every TLB miss.
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/reg.h

@@ -1167,6 +1167,7 @@
 #ifdef CONFIG_PPC_BOOK3S_32
 #define SPRN_SPRG_SCRATCH0	SPRN_SPRG0
 #define SPRN_SPRG_SCRATCH1	SPRN_SPRG1
+#define SPRN_SPRG_PGDIR		SPRN_SPRG2
 #define SPRN_SPRG_603_LRU	SPRN_SPRG4
 #endif
 

arch/powerpc/kernel/cpu_setup_6xx.S

@@ -24,6 +24,10 @@ BEGIN_MMU_FTR_SECTION
 	li	r10,0
 	mtspr	SPRN_SPRG_603_LRU,r10		/* init SW LRU tracking */
 END_MMU_FTR_SECTION_IFSET(MMU_FTR_NEED_DTLB_SW_LRU)
+	lis	r10, (swapper_pg_dir - PAGE_OFFSET)@h
+	ori	r10, r10, (swapper_pg_dir - PAGE_OFFSET)@l
+	mtspr	SPRN_SPRG_PGDIR, r10
+
 BEGIN_FTR_SECTION
 	bl	__init_fpu_registers
 END_FTR_SECTION_IFCLR(CPU_FTR_FPU_UNAVAILABLE)

arch/powerpc/kernel/head_32.S

@@ -500,16 +500,15 @@ InstructionTLBMiss:
 	mfspr	r3,SPRN_IMISS
 	lis	r1,PAGE_OFFSET@h		/* check if kernel address */
 	cmplw	0,r1,r3
-	mfspr	r2,SPRN_SPRG_THREAD
+	mfspr	r2, SPRN_SPRG_PGDIR
 	li	r1,_PAGE_USER|_PAGE_PRESENT|_PAGE_EXEC /* low addresses tested as user */
-	lwz	r2,PGDIR(r2)
 	bge-	112f
 	mfspr	r2,SPRN_SRR1		/* and MSR_PR bit from SRR1 */
 	rlwimi	r1,r2,32-12,29,29	/* shift MSR_PR to _PAGE_USER posn */
 	lis	r2,swapper_pg_dir@ha	/* if kernel address, use */
 	addi	r2,r2,swapper_pg_dir@l	/* kernel page table */
-112:	tophys(r2,r2)
-	rlwimi	r2,r3,12,20,29		/* insert top 10 bits of address */
+	tophys(r2,r2)
+112:	rlwimi	r2,r3,12,20,29		/* insert top 10 bits of address */
 	lwz	r2,0(r2)		/* get pmd entry */
 	rlwinm.	r2,r2,0,0,19		/* extract address of pte page */
 	beq-	InstructionAddressInvalid	/* return if no mapping */
@@ -574,16 +573,15 @@ DataLoadTLBMiss:
 	mfspr	r3,SPRN_DMISS
 	lis	r1,PAGE_OFFSET@h		/* check if kernel address */
 	cmplw	0,r1,r3
-	mfspr	r2,SPRN_SPRG_THREAD
+	mfspr	r2, SPRN_SPRG_PGDIR
 	li	r1,_PAGE_USER|_PAGE_PRESENT /* low addresses tested as user */
-	lwz	r2,PGDIR(r2)
 	bge-	112f
 	mfspr	r2,SPRN_SRR1		/* and MSR_PR bit from SRR1 */
 	rlwimi	r1,r2,32-12,29,29	/* shift MSR_PR to _PAGE_USER posn */
 	lis	r2,swapper_pg_dir@ha	/* if kernel address, use */
 	addi	r2,r2,swapper_pg_dir@l	/* kernel page table */
-112:	tophys(r2,r2)
-	rlwimi	r2,r3,12,20,29		/* insert top 10 bits of address */
+	tophys(r2,r2)
+112:	rlwimi	r2,r3,12,20,29		/* insert top 10 bits of address */
 	lwz	r2,0(r2)		/* get pmd entry */
 	rlwinm.	r2,r2,0,0,19		/* extract address of pte page */
 	beq-	DataAddressInvalid	/* return if no mapping */
@@ -658,16 +656,15 @@ DataStoreTLBMiss:
 	mfspr	r3,SPRN_DMISS
 	lis	r1,PAGE_OFFSET@h		/* check if kernel address */
 	cmplw	0,r1,r3
-	mfspr	r2,SPRN_SPRG_THREAD
+	mfspr	r2, SPRN_SPRG_PGDIR
 	li	r1,_PAGE_RW|_PAGE_USER|_PAGE_PRESENT /* access flags */
-	lwz	r2,PGDIR(r2)
 	bge-	112f
 	mfspr	r2,SPRN_SRR1		/* and MSR_PR bit from SRR1 */
 	rlwimi	r1,r2,32-12,29,29	/* shift MSR_PR to _PAGE_USER posn */
 	lis	r2,swapper_pg_dir@ha	/* if kernel address, use */
 	addi	r2,r2,swapper_pg_dir@l	/* kernel page table */
-112:	tophys(r2,r2)
-	rlwimi	r2,r3,12,20,29		/* insert top 10 bits of address */
+	tophys(r2,r2)
+112:	rlwimi	r2,r3,12,20,29		/* insert top 10 bits of address */
 	lwz	r2,0(r2)		/* get pmd entry */
 	rlwinm.	r2,r2,0,0,19		/* extract address of pte page */
 	beq-	DataAddressInvalid	/* return if no mapping */
@@ -1024,14 +1021,16 @@ _ENTRY(switch_mmu_context)
 	li	r0,NUM_USER_SEGMENTS
 	mtctr	r0
 
+	lwz	r4, MM_PGD(r4)
 #ifdef CONFIG_BDI_SWITCH
 	/* Context switch the PTE pointer for the Abatron BDI2000.
 	 * The PGDIR is passed as second argument.
 	 */
-	lwz	r4,MM_PGD(r4)
 	lis	r5, abatron_pteptrs@ha
 	stw	r4, abatron_pteptrs@l + 0x4(r5)
 #endif
+	tophys(r4, r4)
+	mtspr	SPRN_SPRG_PGDIR, r4
 	li	r4,0
 	isync
 3:

arch/powerpc/mm/hash_low_32.S

@@ -70,9 +70,8 @@ _GLOBAL(hash_page)
 	/* Get PTE (linux-style) and check access */
 	lis	r0,KERNELBASE@h		/* check if kernel address */
 	cmplw	0,r4,r0
-	mfspr	r8,SPRN_SPRG_THREAD	/* current task's THREAD (phys) */
 	ori	r3,r3,_PAGE_USER|_PAGE_PRESENT /* test low addresses as user */
-	lwz	r5,PGDIR(r8)		/* virt page-table root */
+	mfspr	r5, SPRN_SPRG_PGDIR	/* virt page-table root */
 	blt+	112f			/* assume user more likely */
 	lis	r5,swapper_pg_dir@ha	/* if kernel address, use */
 	addi	r5,r5,swapper_pg_dir@l	/* kernel page table */