Subject: [PATCH v2 1/4] powerpc/instruction_dump: Fix kernel crash with show_instructions

From: "Aneesh Kumar K.V" <[email-masked]>
Date: Sun, 24 May 2020 15:08:19 +0530

With Hard Lockup watchdog, we can hit a BUG() if we take a watchdog
interrupt when in OPAL mode. This happens in show_instructions()
where the kernel takes the watchdog NMI IPI with MSR_IR == 0.
With that show_instructions() updates the variable pc in the loop
and the second iterations 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);	\
})

Fixes: 4dd7554a6456 ("powerpc/64: Add VIRTUAL_BUG_ON checks for __va and __pa addresses")
Signed-off-by: Aneesh Kumar K.V <[email-masked]>
---
 arch/powerpc/kernel/process.c | 21 ++++++++++++---------
 1 file changed, 12 insertions(+), 9 deletions(-)

diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index 048d64c4e115..93bf4a766707 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -1253,29 +1253,32 @@ 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 !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);
+		nip = (unsigned long)phys_to_virt(regs->nip);
+	}
+#endif
+
 	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);
-- 
2.26.2