powerpc: Remove use of a second scratch SPRG in STAB code

The STAB code used on Power3 and RS/64 uses a second scratch SPRG to
save a GPR in order to decide whether to go to do_stab_bolted_* or
to handle a normal data access exception.

This prevents our scheme of freeing SPRG3 which is user visible for
user uses since we cannot use SPRG0 which, on RS/64, seems to be
read-only for supervisor mode (like POWER4).

This reworks the STAB exception entry to use the PACA as temporary
storage instead.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

4 files changed, 55 insertions, 30 deletions

diff --git a/arch/powerpc/include/asm/exception-64s.h b/arch/powerpc/include/asm/exception-64s.h
index 773e380b5fe8..a98653b26231 100644
--- a/arch/powerpc/include/asm/exception-64s.h
+++ b/arch/powerpc/include/asm/exception-64s.h
@@ -66,8 +66,7 @@
         std     r9,area+EX_R13(r13);                                    \
         mfcr    r9
 
-#define EXCEPTION_PROLOG_PSERIES(area, label)                           \
-        EXCEPTION_PROLOG_1(area);                                       \
+#define EXCEPTION_PROLOG_PSERIES_1(label)                               \
         ld      r12,PACAKBASE(r13);     /* get high part of &label */   \
         ld      r10,PACAKMSR(r13);      /* get MSR value for kernel */  \
         mfspr   r11,SPRN_SRR0;          /* save SRR0 */                 \
@@ -78,6 +77,10 @@
         rfid;                                                           \
         b       .       /* prevent speculative execution */
 
+#define EXCEPTION_PROLOG_PSERIES(area, label)                           \
+        EXCEPTION_PROLOG_1(area);                                       \
+        EXCEPTION_PROLOG_PSERIES_1(label);
+
 /*
  * The common exception prolog is used for all except a few exceptions
  * such as a segment miss on a kernel address.  We have to be prepared
diff --git a/arch/powerpc/include/asm/reg.h b/arch/powerpc/include/asm/reg.h
index a8179cc99ac4..d17af2b3d4ce 100644
--- a/arch/powerpc/include/asm/reg.h
+++ b/arch/powerpc/include/asm/reg.h
@@ -654,7 +654,7 @@
  * 64-bit server:
  *      - SPRG0 unused (reserved for HV on Power4)
  *      - SPRG1 scratch for exception vectors
- *      - SPRG2 scratch for exception vectors
+ *      - SPRG2 unused
  *
  * All 32-bit:
  *      - SPRG3 current thread_info pointer
@@ -707,7 +707,6 @@
 
 #ifdef CONFIG_PPC_BOOK3S_64
 #define SPRN_SPRG_SCRATCH0      SPRN_SPRG1
-#define SPRN_SPRG_SCRATCH1      SPRN_SPRG2
 #endif
 
 #ifdef CONFIG_PPC_BOOK3S_32
diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
index 4e9640cc0563..50f2ad36ed09 100644
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S
@@ -50,18 +50,28 @@ data_access_pSeries:
         HMT_MEDIUM
         mtspr   SPRN_SPRG_SCRATCH0,r13
 BEGIN_FTR_SECTION
-        mtspr   SPRN_SPRG_SCRATCH1,r12
-        mfspr   r13,SPRN_DAR
-        mfspr   r12,SPRN_DSISR
-        srdi    r13,r13,60
-        rlwimi  r13,r12,16,0x20
-        mfcr    r12
-        cmpwi   r13,0x2c
+        mfspr   r13,SPRN_SPRG_PACA
+        std     r9,PACA_EXSLB+EX_R9(r13)
+        std     r10,PACA_EXSLB+EX_R10(r13)
+        mfspr   r10,SPRN_DAR
+        mfspr   r9,SPRN_DSISR
+        srdi    r10,r10,60
+        rlwimi  r10,r9,16,0x20
+        mfcr    r9
+        cmpwi   r10,0x2c
         beq     do_stab_bolted_pSeries
-        mtcrf   0x80,r12
-        mfspr   r12,SPRN_SPRG_SCRATCH1
-END_FTR_SECTION_IFCLR(CPU_FTR_SLB)
+        ld      r10,PACA_EXSLB+EX_R10(r13)
+        std     r11,PACA_EXGEN+EX_R11(r13)
+        ld      r11,PACA_EXSLB+EX_R9(r13)
+        std     r12,PACA_EXGEN+EX_R12(r13)
+        mfspr   r12,SPRN_SPRG_SCRATCH0
+        std     r10,PACA_EXGEN+EX_R10(r13)
+        std     r11,PACA_EXGEN+EX_R9(r13)
+        std     r12,PACA_EXGEN+EX_R13(r13)
+        EXCEPTION_PROLOG_PSERIES_1(data_access_common)
+FTR_SECTION_ELSE
         EXCEPTION_PROLOG_PSERIES(PACA_EXGEN, data_access_common)
+ALT_FTR_SECTION_END_IFCLR(CPU_FTR_SLB)
 
         . = 0x380
         .globl data_access_slb_pSeries
@@ -224,9 +234,11 @@ masked_interrupt:
 
         .align  7
 do_stab_bolted_pSeries:
-        mtcrf   0x80,r12
-        mfspr   r12,SPRN_SPRG_SCRATCH1
-        EXCEPTION_PROLOG_PSERIES(PACA_EXSLB, .do_stab_bolted)
+        std     r11,PACA_EXSLB+EX_R11(r13)
+        std     r12,PACA_EXSLB+EX_R12(r13)
+        mfspr   r10,SPRN_SPRG_SCRATCH0
+        std     r10,PACA_EXSLB+EX_R13(r13)
+        EXCEPTION_PROLOG_PSERIES_1(.do_stab_bolted)
 
 #ifdef CONFIG_PPC_PSERIES
 /*
diff --git a/arch/powerpc/platforms/iseries/exception.S b/arch/powerpc/platforms/iseries/exception.S
index 2b8075979237..5369653dcf6a 100644
--- a/arch/powerpc/platforms/iseries/exception.S
+++ b/arch/powerpc/platforms/iseries/exception.S
@@ -128,25 +128,36 @@ iSeries_secondary_smp_loop:
 data_access_iSeries:
         mtspr   SPRN_SPRG_SCRATCH0,r13
 BEGIN_FTR_SECTION
-        mtspr   SPRN_SPRG_SCRATCH1,r12
-        mfspr   r13,SPRN_DAR
-        mfspr   r12,SPRN_DSISR
-        srdi    r13,r13,60
-        rlwimi  r13,r12,16,0x20
-        mfcr    r12
-        cmpwi   r13,0x2c
+        mfspr   r13,SPRN_SPRG_PACA
+        std     r9,PACA_EXSLB+EX_R9(r13)
+        std     r10,PACA_EXSLB+EX_R10(r13)
+        mfspr   r10,SPRN_DAR
+        mfspr   r9,SPRN_DSISR
+        srdi    r10,r10,60
+        rlwimi  r10,r9,16,0x20
+        mfcr    r9
+        cmpwi   r10,0x2c
         beq     .do_stab_bolted_iSeries
-        mtcrf   0x80,r12
-        mfspr   r12,SPRN_SPRG_SCRATCH1
-END_FTR_SECTION_IFCLR(CPU_FTR_SLB)
+        ld      r10,PACA_EXSLB+EX_R10(r13)
+        std     r11,PACA_EXGEN+EX_R11(r13)
+        ld      r11,PACA_EXSLB+EX_R9(r13)
+        std     r12,PACA_EXGEN+EX_R12(r13)
+        mfspr   r12,SPRN_SPRG_SCRATCH0
+        std     r10,PACA_EXGEN+EX_R10(r13)
+        std     r11,PACA_EXGEN+EX_R9(r13)
+        std     r12,PACA_EXGEN+EX_R13(r13)
+        EXCEPTION_PROLOG_ISERIES_1
+FTR_SECTION_ELSE
         EXCEPTION_PROLOG_1(PACA_EXGEN)
         EXCEPTION_PROLOG_ISERIES_1
+ALT_FTR_SECTION_END_IFCLR(CPU_FTR_SLB)
         b       data_access_common
 
 .do_stab_bolted_iSeries:
-        mtcrf   0x80,r12
-        mfspr   r12,SPRN_SPRG_SCRATCH1
-        EXCEPTION_PROLOG_1(PACA_EXSLB)
+        std     r11,PACA_EXSLB+EX_R11(r13)
+        std     r12,PACA_EXSLB+EX_R12(r13)
+        mfspr   r10,SPRN_SPRG_SCRATCH0
+        std     r10,PACA_EXSLB+EX_R13(r13)
         EXCEPTION_PROLOG_ISERIES_1
         b       .do_stab_bolted