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Date:   Thu, 18 Apr 2019 17:07:45 -0700
From:   "Luck, Tony" <>
To:     Borislav Petkov <>
Cc:     Cong Wang <>,
        LKML <>
Subject: Re: [PATCH] RAS/CEC: Add debugfs switch to disable at run time

On Fri, Apr 19, 2019 at 01:29:10AM +0200, Borislav Petkov wrote:
> Which reminds me, Tony, I think all those debugging files "pfn"
> and "array" and the one you add now, should all be under a
> CONFIG_RAS_CEC_DEBUG which is default off and used only for development.
> Mind adding that too pls?

Patch below, on top of previous patch.  Note that I didn't move "enable"
into the RAS_CEC_DEBUG code. I think it has some value even on
production systems.  It is still in debugfs (which many production
systems don't mount) so I don't see that people are going to be randomly
using it to disable the CEC.


>From ac9d8c9bf7b38e18dcffdd41f8fcf0f07c632cd3 Mon Sep 17 00:00:00 2001
From: Tony Luck <>
Date: Thu, 18 Apr 2019 16:46:55 -0700
Subject: [PATCH] RAS/CEC: Move CEC debug features under a CONFIG_RAS_CEC_DEBUG

The pfn and array files in /sys/kernel/debug/ras/cec are intended
for debugging the CEC code itself. They are not needed on production
systems, so the default setting for this CONFIG option is "n".

Signed-off-by: Tony Luck <>
 arch/x86/ras/Kconfig | 10 ++++++++++
 drivers/ras/cec.c    | 13 ++++++++++++-
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/arch/x86/ras/Kconfig b/arch/x86/ras/Kconfig
index a9c3db125222..7fde8d55e394 100644
--- a/arch/x86/ras/Kconfig
+++ b/arch/x86/ras/Kconfig
@@ -11,3 +11,13 @@ config RAS_CEC
 	  Bear in mind that this is absolutely useless if your platform doesn't
 	  have ECC DIMMs and doesn't have DRAM ECC checking enabled in the BIOS.
+	bool "Debugging"
+	default n
+	depends on RAS_CEC
+	---help---
+	  Add extra files to /sys/kernel/debug/ras/cec to test the correctable
+	  memory error feature. "pfn" is a writable file that allows user to
+	  simulate an error in a particular page frame. "array" is a read-only
+	  file that dumps out the current state of all pages logged so far.
diff --git a/drivers/ras/cec.c b/drivers/ras/cec.c
index a2ceedcd8516..ff880a5c289a 100644
--- a/drivers/ras/cec.c
+++ b/drivers/ras/cec.c
@@ -118,7 +118,9 @@ static struct ce_array {
 } ce_arr;
 static DEFINE_MUTEX(ce_mutex);
 static u64 dfs_pfn;
 /* Amount of errors after which we offline */
 static unsigned int count_threshold = COUNT_MASK;
@@ -364,6 +366,7 @@ static int u64_get(void *data, u64 *val)
 	return 0;
 static int pfn_set(void *data, u64 val)
 	*(u64 *)data = val;
@@ -372,6 +375,7 @@ static int pfn_set(void *data, u64 val)
 DEFINE_DEBUGFS_ATTRIBUTE(pfn_ops, u64_get, pfn_set, "0x%llx\n");
 static int decay_interval_set(void *data, u64 val)
@@ -411,6 +415,7 @@ static int enable_set(void *data, u64 val)
 DEFINE_DEBUGFS_ATTRIBUTE(enable_ops, u64_get, enable_set, "%lld\n");
 static int array_dump(struct seq_file *m, void *v)
 	struct ce_array *ca = &ce_arr;
@@ -459,10 +464,14 @@ static const struct file_operations array_ops = {
 	.llseek	 = seq_lseek,
 	.release = single_release,
 static int __init create_debugfs_nodes(void)
-	struct dentry *d, *pfn, *decay, *count, *array, *enable;
+	struct dentry *d, *decay, *count, *enable;
+	struct dentry *pfn, *array;
 	d = debugfs_create_dir("cec", ras_debugfs_dir);
 	if (!d) {
@@ -470,6 +479,7 @@ static int __init create_debugfs_nodes(void)
 		return -1;
 	pfn = debugfs_create_file("pfn", S_IRUSR | S_IWUSR, d, &dfs_pfn, &pfn_ops);
 	if (!pfn) {
 		pr_warn("Error creating pfn debugfs node!\n");
@@ -481,6 +491,7 @@ static int __init create_debugfs_nodes(void)
 		pr_warn("Error creating array debugfs node!\n");
 		goto err;
 	decay = debugfs_create_file("decay_interval", S_IRUSR | S_IWUSR, d,
 				    &timer_interval, &decay_interval_ops);

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