powerpc: Fix kernel crash in show_instructions() w/DEBUG_VIRTUAL

With CONFIG_DEBUG_VIRTUAL=y, we can hit a BUG() if we take a hard
lockup watchdog interrupt when in OPAL mode.

This happens in show_instructions() if the kernel takes the watchdog
NMI IPI, or any other interrupt, with MSR_IR == 0. show_instructions()
updates the variable pc in the loop and the second iteration will
result in BUG().

We hit the BUG_ON due the below check in  __va()

  #define __va(x)
  ({
  	VIRTUAL_BUG_ON((unsigned long)(x) >= PAGE_OFFSET);
  	(void *)(unsigned long)((phys_addr_t)(x) | PAGE_OFFSET);
  })

Fix it by moving the check out of the loop. Also update nip so that
the nip == pc check still matches.

Fixes: 4dd7554a6456 ("powerpc/64: Add VIRTUAL_BUG_ON checks for __va and __pa addresses")
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
[mpe: Use IS_ENABLED(), massage change log]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200524093822.423487-1-aneesh.kumar@linux.ibm.com

diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index 7bb7faf..a2f1f0e 100644 (file)
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -1252,29 +1252,31 @@ struct task_struct *__switch_to(struct task_struct *prev,
 static void show_instructions(struct pt_regs *regs)
 {
        int i;
+       unsigned long nip = regs->nip;
        unsigned long pc = regs->nip - (NR_INSN_TO_PRINT * 3 / 4 * sizeof(int));
 
        printk("Instruction dump:");
 
+       /*
+        * If we were executing with the MMU off for instructions, adjust pc
+        * rather than printing XXXXXXXX.
+        */
+       if (!IS_ENABLED(CONFIG_BOOKE) && !(regs->msr & MSR_IR)) {
+               pc = (unsigned long)phys_to_virt(pc);
+               nip = (unsigned long)phys_to_virt(regs->nip);
+       }
+
        for (i = 0; i < NR_INSN_TO_PRINT; i++) {
                int instr;
 
                if (!(i % 8))
                        pr_cont("\n");
 
-#if !defined(CONFIG_BOOKE)
-               /* If executing with the IMMU off, adjust pc rather
-                * than print XXXXXXXX.
-                */
-               if (!(regs->msr & MSR_IR))
-                       pc = (unsigned long)phys_to_virt(pc);
-#endif
-
                if (!__kernel_text_address(pc) ||
                    probe_kernel_address((const void *)pc, instr)) {
                        pr_cont("XXXXXXXX ");
                } else {
-                       if (regs->nip == pc)
+                       if (nip == pc)
                                pr_cont("<%08x> ", instr);
                        else
                                pr_cont("%08x ", instr);