powerpc/booke64: Use SPRG0/3 scratch for bolted TLB miss & crit int

Embedded.Hypervisor category defines GSPRG0..3 physical registers for guests.
Avoid SPRG4-7 usage as scratch in host exception handlers, otherwise guest
SPRG4-7 registers will be clobbered.
For bolted TLB miss exception handlers, which is the version currently
supported by KVM, use SPRN_SPRG_GEN_SCRATCH aka SPRG0 instead of
SPRN_SPRG_TLB_SCRATCH aka SPRG6. Keep using TLB PACA slots to fit in one
64-byte cache line.
For critical exception handlers use SPRG3 instead of SPRG7. Provide a routine
to store and restore user-visible SPRGs. This will be subsequently used
to restore VDSO information in SPRG3. Add EX_R13 to paca slots to free up
SPRG3 and change the critical exception epilog to use it.

Signed-off-by: Mihai Caraman <mihai.caraman@freescale.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/include/asm/exception-64e.h

@@ -46,8 +46,9 @@
 #define EX_CR		(1 * 8)
 #define EX_R10		(2 * 8)
 #define EX_R11		(3 * 8)
-#define EX_R14		(4 * 8)
-#define EX_R15		(5 * 8)
+#define EX_R13		(4 * 8)
+#define EX_R14		(5 * 8)
+#define EX_R15		(6 * 8)
 
 /*
  * The TLB miss exception uses different slots.

arch/powerpc/include/asm/reg.h

@@ -761,7 +761,8 @@
  * 64-bit embedded
  *	- SPRG0 generic exception scratch
  *	- SPRG2 TLB exception stack
- *	- SPRG3 CPU and NUMA node for VDSO getcpu (user visible)
+ *	- SPRG3 critical exception scratch and
+ *        CPU and NUMA node for VDSO getcpu (user visible)
  *	- SPRG4 unused (user visible)
  *	- SPRG6 TLB miss scratch (user visible, sorry !)
  *	- SPRG7 critical exception scratch
@@ -858,7 +859,7 @@
 
 #ifdef CONFIG_PPC_BOOK3E_64
 #define SPRN_SPRG_MC_SCRATCH	SPRN_SPRG8
-#define SPRN_SPRG_CRIT_SCRATCH	SPRN_SPRG7
+#define SPRN_SPRG_CRIT_SCRATCH	SPRN_SPRG3
 #define SPRN_SPRG_DBG_SCRATCH	SPRN_SPRG9
 #define SPRN_SPRG_TLB_EXFRAME	SPRN_SPRG2
 #define SPRN_SPRG_TLB_SCRATCH	SPRN_SPRG6

arch/powerpc/kernel/exceptions-64e.S

@@ -42,6 +42,7 @@
 	mfspr	r13,SPRN_SPRG_PACA;	/* get PACA */			    \
 	std	r10,PACA_EX##type+EX_R10(r13);				    \
 	std	r11,PACA_EX##type+EX_R11(r13);				    \
+	PROLOG_STORE_RESTORE_SCRATCH_##type;				    \
 	mfcr	r10;			/* save CR */			    \
 	mfspr	r11,SPRN_##type##_SRR1;/* what are we coming from */	    \
 	DO_KVM	intnum,SPRN_##type##_SRR1;    /* KVM hook */		    \
@@ -99,6 +100,18 @@
 #define GDBELL_EXCEPTION_PROLOG(n, intnum, addition)			    \
 	EXCEPTION_PROLOG(n, intnum, GDBELL, addition##_GDBELL(n))
 
+/*
+ * Store user-visible scratch in PACA exception slots and restore proper value
+ */
+#define PROLOG_STORE_RESTORE_SCRATCH_GEN
+#define PROLOG_STORE_RESTORE_SCRATCH_GDBELL
+#define PROLOG_STORE_RESTORE_SCRATCH_DBG
+#define PROLOG_STORE_RESTORE_SCRATCH_MC
+
+#define PROLOG_STORE_RESTORE_SCRATCH_CRIT				    \
+	mfspr	r10,SPRN_SPRG_CRIT_SCRATCH;	/* get r13 */		    \
+	std	r10,PACA_EXCRIT+EX_R13(r13)
+
 /* Variants of the "addition" argument for the prolog
  */
 #define PROLOG_ADDITION_NONE_GEN(n)
@@ -454,7 +467,7 @@ interrupt_end_book3e:
 	mtcr	r10
 	ld	r10,PACA_EXCRIT+EX_R10(r13)	/* restore registers */
 	ld	r11,PACA_EXCRIT+EX_R11(r13)
-	mfspr	r13,SPRN_SPRG_CRIT_SCRATCH
+	ld	r13,PACA_EXCRIT+EX_R13(r13)
 	rfci
 
 	/* Normal debug exception */
@@ -467,7 +480,7 @@ interrupt_end_book3e:
 	/* Now we mash up things to make it look like we are coming on a
 	 * normal exception
 	 */
-	mfspr	r15,SPRN_SPRG_CRIT_SCRATCH
+	ld	r15,PACA_EXCRIT+EX_R13(r13)
 	mtspr	SPRN_SPRG_GEN_SCRATCH,r15
 	mfspr	r14,SPRN_DBSR
 	EXCEPTION_COMMON(0xd00, PACA_EXCRIT, INTS_DISABLE)

arch/powerpc/mm/tlb_low_64e.S

@@ -40,7 +40,7 @@
  **********************************************************************/
 
 .macro tlb_prolog_bolted intnum addr
-	mtspr	SPRN_SPRG_TLB_SCRATCH,r13
+	mtspr	SPRN_SPRG_GEN_SCRATCH,r13
 	mfspr	r13,SPRN_SPRG_PACA
 	std	r10,PACA_EXTLB+EX_TLB_R10(r13)
 	mfcr	r10
@@ -69,7 +69,7 @@ END_FTR_SECTION_IFSET(CPU_FTR_EMB_HV)
 	ld	r15,PACA_EXTLB+EX_TLB_R15(r13)
 	TLB_MISS_RESTORE_STATS_BOLTED
 	ld	r16,PACA_EXTLB+EX_TLB_R16(r13)
-	mfspr	r13,SPRN_SPRG_TLB_SCRATCH
+	mfspr	r13,SPRN_SPRG_GEN_SCRATCH
 .endm
 
 /* Data TLB miss */