powerpc: show registers when unwinding interrupt frames

It's often useful to know the register state for interrupts in
the stack frame. In the below example (with this patch applied),
the important information is the state of the page fault.

A blatant case like this probably rather should have the page
fault regs passed down to the warning, but quite often there are
less obvious cases where an interrupt shows up that might give
some more clues.

The downside is longer and more complex bug output.

  Bug: Write fault blocked by AMR!
  WARNING: CPU: 0 PID: 72 at arch/powerpc/include/asm/book3s/64/kup-radix.h:164 __do_page_fault+0x880/0xa90
  Modules linked in:
  CPU: 0 PID: 72 Comm: systemd-gpt-aut Not tainted
  NIP:  c00000000006e2f0 LR: c00000000006e2ec CTR: 0000000000000000
  REGS: c00000000a4f3420 TRAP: 0700
  MSR:  8000000000021033 <SF,ME,IR,DR,RI,LE>  CR: 28002840  XER: 20040000
  CFAR: c000000000128be0 IRQMASK: 3
  GPR00: c00000000006e2ec c00000000a4f36c0 c0000000014f0700 0000000000000020
  GPR04: 0000000000000001 c000000001290f50 0000000000000001 c000000001290f80
  GPR08: c000000001612b08 0000000000000000 0000000000000000 00000000ffffe0f7
  GPR12: 0000000048002840 c0000000016e0000 c00c000000021c80 c000000000fd6f60
  GPR16: 0000000000000000 c00000000a104698 0000000000000003 c0000000087f0000
  GPR20: 0000000000000100 c0000000070330b8 0000000000000000 0000000000000004
  GPR24: 0000000002000000 0000000000000300 0000000002000000 c00000000a5b0c00
  GPR28: 0000000000000000 000000000a000000 00007fffb2a90038 c00000000a4f3820
  NIP [c00000000006e2f0] __do_page_fault+0x880/0xa90
  LR [c00000000006e2ec] __do_page_fault+0x87c/0xa90
  Call Trace:
  [c00000000a4f36c0] [c00000000006e2ec] __do_page_fault+0x87c/0xa90 (unreliable)
  [c00000000a4f3780] [c000000000e1c034] do_page_fault+0x34/0x90
  [c00000000a4f37b0] [c000000000008908] data_access_common_virt+0x158/0x1b0
  --- interrupt: 300 at __copy_tofrom_user_base+0x9c/0x5a4
  NIP:  c00000000009b028 LR: c000000000802978 CTR: 0000000000000800
  REGS: c00000000a4f3820 TRAP: 0300
  MSR:  800000000280b033 <SF,VEC,VSX,EE,FP,ME,IR,DR,RI,LE>  CR: 24004840  XER: 00000000
  CFAR: c00000000009aff4 DAR: 00007fffb2a90038 DSISR: 0a000000 IRQMASK: 0
  GPR00: 0000000000000000 c00000000a4f3ac0 c0000000014f0700 00007fffb2a90028
  GPR04: c000000008720010 0000000000010000 0000000000000000 0000000000000000
  GPR08: 0000000000000000 0000000000000000 0000000000000000 0000000000000001
  GPR12: 0000000000004000 c0000000016e0000 c00c000000021c80 c000000000fd6f60
  GPR16: 0000000000000000 c00000000a104698 0000000000000003 c0000000087f0000
  GPR20: 0000000000000100 c0000000070330b8 0000000000000000 0000000000000004
  GPR24: c00000000a4f3c80 c000000008720000 0000000000010000 0000000000000000
  GPR28: 0000000000010000 0000000008720000 0000000000010000 c000000001515b98
  NIP [c00000000009b028] __copy_tofrom_user_base+0x9c/0x5a4
  LR [c000000000802978] copyout+0x68/0xc0
  --- interrupt: 300
  [c00000000a4f3af0] [c0000000008074b8] copy_page_to_iter+0x188/0x540
  [c00000000a4f3b50] [c00000000035c678] generic_file_buffered_read+0x358/0xd80
  [c00000000a4f3c40] [c0000000004c1e90] blkdev_read_iter+0x50/0x80
  [c00000000a4f3c60] [c00000000045733c] new_sync_read+0x12c/0x1c0
  [c00000000a4f3d00] [c00000000045a1f0] vfs_read+0x1d0/0x240
  [c00000000a4f3d50] [c00000000045a7f4] ksys_read+0x84/0x140
  [c00000000a4f3da0] [c000000000033a60] system_call_exception+0x100/0x280
  [c00000000a4f3e10] [c00000000000c508] system_call_common+0xf8/0x2f8
  Instruction dump:
  eae10078 3be0000b 4bfff890 60420000 792917e1 4182ff18 3c82ffab 3884a5e0
  3c62ffab 3863a6e8 480ba891 60000000 <0fe00000> 3be0000b 4bfff860 e93c0938

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20201107023305.2384874-1-npiggin@gmail.com

arch/powerpc/kernel/process.c

@@ -1466,12 +1466,10 @@ static void print_msr_bits(unsigned long val)
 #define LAST_VOLATILE	12
 #endif
 
-void show_regs(struct pt_regs * regs)
+static void __show_regs(struct pt_regs *regs)
 {
 	int i, trap;
 
-	show_regs_print_info(KERN_DEFAULT);
-
 	printk("NIP:  "REG" LR: "REG" CTR: "REG"\n",
 	       regs->nip, regs->link, regs->ctr);
 	printk("REGS: %px TRAP: %04lx   %s  (%s)\n",
@@ -1513,6 +1511,12 @@ void show_regs(struct pt_regs * regs)
 		printk("NIP ["REG"] %pS\n", regs->nip, (void *)regs->nip);
 		printk("LR ["REG"] %pS\n", regs->link, (void *)regs->link);
 	}
+}
+
+void show_regs(struct pt_regs *regs)
+{
+	show_regs_print_info(KERN_DEFAULT);
+	__show_regs(regs);
 	show_stack(current, (unsigned long *) regs->gpr[1], KERN_DEFAULT);
 	if (!user_mode(regs))
 		show_instructions(regs);
@@ -2178,10 +2182,14 @@ void show_stack(struct task_struct *tsk, unsigned long *stack,
 		    && stack[STACK_FRAME_MARKER] == STACK_FRAME_REGS_MARKER) {
 			struct pt_regs *regs = (struct pt_regs *)
 				(sp + STACK_FRAME_OVERHEAD);
+
 			lr = regs->link;
-			printk("%s--- interrupt: %lx at %pS\n    LR = %pS\n",
-			       loglvl, regs->trap,
-			       (void *)regs->nip, (void *)lr);
+			printk("%s--- interrupt: %lx at %pS\n",
+			       loglvl, regs->trap, (void *)regs->nip);
+			__show_regs(regs);
+			printk("%s--- interrupt: %lx\n",
+			       loglvl, regs->trap);
+
 			firstframe = 1;
 		}