Re: [PATCH] arm: mm: fault: check ADFSR in case of abort

From: Robin Murphy
Date: Mon Oct 29 2018 - 10:52:06 EST


On 29/10/2018 14:20, Wiebe, Wladislav (Nokia - DE/Ulm) wrote:
When running into situations like:
"Unhandled fault: synchronous external abort (0x210) at 0xXXX"
or
"Unhandled prefetch abort: synchronous external abort (0x210) at 0xXXX"
it is useful to know the content of ADFSR (Auxiliary Data Fault Status
Register) to indicate an ECC double-bit error in L1 or L2 cache.

Refer to:
Cortex-A15 Technical Reference Manual, Revision: r2p1
[6.4.8. Error Correction Code]

The contents of ADFSR are implementation-defined, though, so this interpretation is *only* valid on Cortex-A15. Other processors may use those bit positions to report something else, at which point printing a message about ECC errors would be totally misleading.

Robin.

Signed-off-by: Wladislav Wiebe <wladislav.wiebe@xxxxxxxxx>
---
arch/arm/mm/fault.c | 18 ++++++++++++++++++
1 file changed, 18 insertions(+)

diff --git a/arch/arm/mm/fault.c b/arch/arm/mm/fault.c
index 3232afb6fdc0..5e240deb6ed6 100644
--- a/arch/arm/mm/fault.c
+++ b/arch/arm/mm/fault.c
@@ -547,6 +547,22 @@ hook_fault_code(int nr, int (*fn)(unsigned long, unsigned int, struct pt_regs *)
fsr_info[nr].name = name;
}
+/*
+ * Check for ECC double-bit errors in Auxiliary Data Fault Status Register
+ */
+static void check_adfsr_for_ecc(void)
+{
+ u32 adfsr = 0;
+
+ asm("mrc p15, 0, %0, c5, c1, 0" : "=r" (adfsr));
+
+ if (adfsr & (BIT(31) | BIT(23))) {
+ pr_alert("ADFSR status 0x%x indicates that an L1 or L2 cache\n"
+ "ECC double-bit error occurred at some time.\n",
+ adfsr);
+ }
+}
+
/*
* Dispatch a data abort to the relevant handler.
*/
@@ -559,6 +575,7 @@ do_DataAbort(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
if (!inf->fn(addr, fsr & ~FSR_LNX_PF, regs))
return;
+ check_adfsr_for_ecc();
pr_alert("Unhandled fault: %s (0x%03x) at 0x%08lx\n",
inf->name, fsr, addr);
show_pte(current->mm, addr);
@@ -593,6 +610,7 @@ do_PrefetchAbort(unsigned long addr, unsigned int ifsr, struct pt_regs *regs)
if (!inf->fn(addr, ifsr | FSR_LNX_PF, regs))
return;
+ check_adfsr_for_ecc();
pr_alert("Unhandled prefetch abort: %s (0x%03x) at 0x%08lx\n",
inf->name, ifsr, addr);