linux-kernel - [PATCH] arm64: translate register values to physical addresses in kernel panics

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Date:   Fri, 12 Aug 2022 11:35:30 -0700
From:   Peter Collingbourne <pcc@...gle.com>
To:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Mark Brown <broonie@...nel.org>,
        Mark Rutland <mark.rutland@....com>
Cc:     Peter Collingbourne <pcc@...gle.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: [PATCH] arm64: translate register values to physical addresses in
 kernel panics

When debugging a kernel panic it is sometimes useful to know the physical
address of any virtual addresses stored in registers. Therefore, pass
all register values through AT S1E1R and print the resulting PAR_EL1
value next to the register.

Signed-off-by: Peter Collingbourne <pcc@...gle.com>
Link: https://linux-review.googlesource.com/id/I7c6be65f27052da57088ff58b463fdbe2394f43c
---
Not sure if this should land in this form (I imagine there could be
all kinds of parsers that are expecting the existing format) but
maybe behind an option. Let me know what you think.

 arch/arm64/kernel/process.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index 92bcc1768f0b..8b5f8c2c8abf 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -197,6 +197,18 @@ static void print_pstate(struct pt_regs *regs)
 	}
 }
 
+static unsigned long at(unsigned long addr)
+{
+	unsigned long pa;
+
+	__asm__ __volatile__("at s1e1r, %1\n"
+			     "mrs %0, par_el1\n"
+			     : "=r"(pa)
+			     : "r"(addr)
+			     : "memory");
+	return pa;
+}
+
 void __show_regs(struct pt_regs *regs)
 {
 	int i, top_reg;
@@ -231,10 +243,10 @@ void __show_regs(struct pt_regs *regs)
 	i = top_reg;
 
 	while (i >= 0) {
-		printk("x%-2d: %016llx", i, regs->regs[i]);
+		printk("x%-2d: %016llx (%016llx)", i, regs->regs[i], at(regs->regs[i]));
 
 		while (i-- % 3)
-			pr_cont(" x%-2d: %016llx", i, regs->regs[i]);
+			pr_cont(" x%-2d: %016llx (%016llx)", i, regs->regs[i], at(regs->regs[i]));
 
 		pr_cont("\n");
 	}
-- 
2.37.1.595.g718a3a8f04-goog