powerpc: Save Come-From Address Register (CFAR) in exception frame

Recent 64-bit server processors (POWER6 and POWER7) have a "Come-From
Address Register" (CFAR), that records the address of the most recent
branch or rfid (return from interrupt) instruction for debugging purposes.

This saves the value of the CFAR in the exception entry code and stores
it in the exception frame.  We also make xmon print the CFAR value in
its register dump code.

Rather than extend the pt_regs struct at this time, we steal the orig_gpr3
field, which is only used for system calls, and use it for the CFAR value
for all exceptions/interrupts other than system calls.  This means we
don't save the CFAR on system calls, which is not a great problem since
system calls tend not to happen unexpectedly, and also avoids adding the
overhead of reading the CFAR to the system call entry path.

Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

6 files changed, 24 insertions, 5 deletions

diff --git a/arch/powerpc/include/asm/cputable.h b/arch/powerpc/include/asm/cputable.h
index a3e1a9e96a7..4efbfb3f325 100644
--- a/arch/powerpc/include/asm/cputable.h
+++ b/arch/powerpc/include/asm/cputable.h
@@ -180,6 +180,7 @@ extern const char *powerpc_base_platform;
 
 
 #define CPU_FTR_HVMODE_206              LONG_ASM_CONST(0x0000000800000000)
+#define CPU_FTR_CFAR                    LONG_ASM_CONST(0x0000001000000000)
 #define CPU_FTR_IABR                    LONG_ASM_CONST(0x0000002000000000)
 #define CPU_FTR_MMCRA                   LONG_ASM_CONST(0x0000004000000000)
 #define CPU_FTR_CTRL                    LONG_ASM_CONST(0x0000008000000000)
@@ -412,7 +413,7 @@ extern const char *powerpc_base_platform;
             CPU_FTR_COHERENT_ICACHE | \
             CPU_FTR_PURR | CPU_FTR_SPURR | CPU_FTR_REAL_LE | \
             CPU_FTR_DSCR | CPU_FTR_UNALIGNED_LD_STD | \
-            CPU_FTR_STCX_CHECKS_ADDRESS | CPU_FTR_POPCNTB)
+            CPU_FTR_STCX_CHECKS_ADDRESS | CPU_FTR_POPCNTB | CPU_FTR_CFAR)
 #define CPU_FTRS_POWER7 (CPU_FTR_USE_TB | CPU_FTR_LWSYNC | \
             CPU_FTR_PPCAS_ARCH_V2 | CPU_FTR_CTRL | CPU_FTR_HVMODE_206 |\
             CPU_FTR_MMCRA | CPU_FTR_SMT | \
@@ -420,7 +421,7 @@ extern const char *powerpc_base_platform;
             CPU_FTR_PURR | CPU_FTR_SPURR | CPU_FTR_REAL_LE | \
             CPU_FTR_DSCR | CPU_FTR_SAO  | CPU_FTR_ASYM_SMT | \
             CPU_FTR_STCX_CHECKS_ADDRESS | CPU_FTR_POPCNTB | CPU_FTR_POPCNTD | \
-            CPU_FTR_ICSWX)
+            CPU_FTR_ICSWX | CPU_FTR_CFAR)
 #define CPU_FTRS_CELL   (CPU_FTR_USE_TB | CPU_FTR_LWSYNC | \
             CPU_FTR_PPCAS_ARCH_V2 | CPU_FTR_CTRL | \
             CPU_FTR_ALTIVEC_COMP | CPU_FTR_MMCRA | CPU_FTR_SMT | \
diff --git a/arch/powerpc/include/asm/exception-64s.h b/arch/powerpc/include/asm/exception-64s.h
index 96ccef136ca..f5dfe3411f6 100644
--- a/arch/powerpc/include/asm/exception-64s.h
+++ b/arch/powerpc/include/asm/exception-64s.h
@@ -46,6 +46,7 @@
 #define EX_CCR          60
 #define EX_R3           64
 #define EX_LR           72
+#define EX_CFAR         80
 
 /*
  * We're short on space and time in the exception prolog, so we can't
@@ -66,6 +67,10 @@
         std     r10,area+EX_R10(r13);                                   \
         std     r11,area+EX_R11(r13);                                   \
         std     r12,area+EX_R12(r13);                                   \
+        BEGIN_FTR_SECTION_NESTED(66);                                   \
+        mfspr   r10,SPRN_CFAR;                                          \
+        std     r10,area+EX_CFAR(r13);                                  \
+        END_FTR_SECTION_NESTED(CPU_FTR_CFAR, CPU_FTR_CFAR, 66);         \
         GET_SCRATCH0(r9);                                               \
         std     r9,area+EX_R13(r13);                                    \
         mfcr    r9
@@ -130,6 +135,10 @@
         std     r9,GPR11(r1);                                              \
         std     r10,GPR12(r1);                                             \
         std     r11,GPR13(r1);                                             \
+        BEGIN_FTR_SECTION_NESTED(66);                                      \
+        ld      r10,area+EX_CFAR(r13);                                     \
+        std     r10,ORIG_GPR3(r1);                                         \
+        END_FTR_SECTION_NESTED(CPU_FTR_CFAR, CPU_FTR_CFAR, 66);            \
         ld      r2,PACATOC(r13);        /* get kernel TOC into r2       */ \
         mflr    r9;                     /* save LR in stackframe        */ \
         std     r9,_LINK(r1);                                              \
diff --git a/arch/powerpc/include/asm/paca.h b/arch/powerpc/include/asm/paca.h
index 65c13c48db4..74126765106 100644
--- a/arch/powerpc/include/asm/paca.h
+++ b/arch/powerpc/include/asm/paca.h
@@ -92,9 +92,9 @@ struct paca_struct {
          * Now, starting in cacheline 2, the exception save areas
          */
         /* used for most interrupts/exceptions */
-        u64 exgen[10] __attribute__((aligned(0x80)));
-        u64 exmc[10];           /* used for machine checks */
-        u64 exslb[10];          /* used for SLB/segment table misses
+        u64 exgen[11] __attribute__((aligned(0x80)));
+        u64 exmc[11];           /* used for machine checks */
+        u64 exslb[11];          /* used for SLB/segment table misses
                                  * on the linear mapping */
         /* SLB related definitions */
         u16 vmalloc_sllp;
diff --git a/arch/powerpc/include/asm/reg.h b/arch/powerpc/include/asm/reg.h
index 632e78e1444..fdec5933305 100644
--- a/arch/powerpc/include/asm/reg.h
+++ b/arch/powerpc/include/asm/reg.h
@@ -188,6 +188,7 @@
 
 #define SPRN_CTR        0x009   /* Count Register */
 #define SPRN_DSCR       0x11
+#define SPRN_CFAR       0x1c    /* Come From Address Register */
 #define SPRN_ACOP       0x1F    /* Available Coprocessor Register */
 #define SPRN_CTRLF      0x088
 #define SPRN_CTRLT      0x098
diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
index 27ca8b7c600..0ec3b42717d 100644
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S
@@ -474,6 +474,10 @@ bad_stack:
         std     r9,GPR11(r1)
         std     r10,GPR12(r1)
         std     r11,GPR13(r1)
+BEGIN_FTR_SECTION
+        ld      r10,EX_CFAR(r3)
+        std     r10,ORIG_GPR3(r1)
+END_FTR_SECTION_IFSET(CPU_FTR_CFAR)
         SAVE_8GPRS(14,r1)
         SAVE_10GPRS(22,r1)
         lhz     r12,PACA_TRAP_SAVE(r13)
diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
index 60593ad861e..909804aaeeb 100644
--- a/arch/powerpc/xmon/xmon.c
+++ b/arch/powerpc/xmon/xmon.c
@@ -1497,6 +1497,10 @@ static void prregs(struct pt_regs *fp)
 #endif
         printf("pc  = ");
         xmon_print_symbol(fp->nip, " ", "\n");
+        if (TRAP(fp) != 0xc00 && cpu_has_feature(CPU_FTR_CFAR)) {
+                printf("cfar= ");
+                xmon_print_symbol(fp->orig_gpr3, " ", "\n");
+        }
         printf("lr  = ");
         xmon_print_symbol(fp->link, " ", "\n");
         printf("msr = "REG"   cr  = %.8lx\n", fp->msr, fp->ccr);