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Subject[PATCH v3] x86/mce: Honour bios-set CMCI threshold
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Date
The ACPI spec doesn't provide for a way for the bios to pass down
recommended thresholds to the OS on a _per-bank_ basis. This patch adds
a new boot option, which if passed, allows bios to initialize the CMCI
threshold. In such a case, we simply skip programming any threshold
value.

As fail-safe, we initialize threshold to 1 if some banks have not been
initialized by the bios and warn the user.

v3: Updated messages as per Tony's inputs.
v2: Just separating out the patch. I will send a separate patch for
consolidating the MCE boot flags.

Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
---
Documentation/x86/x86_64/boot-options.txt | 5 ++++
arch/x86/include/asm/mce.h | 1 +
arch/x86/kernel/cpu/mcheck/mce.c | 10 ++++++++
arch/x86/kernel/cpu/mcheck/mce_intel.c | 35 +++++++++++++++++++++++++++--
4 files changed, 48 insertions(+), 3 deletions(-)

diff --git a/Documentation/x86/x86_64/boot-options.txt b/Documentation/x86/x86_64/boot-options.txt
index c54b4f5..ec92540 100644
--- a/Documentation/x86/x86_64/boot-options.txt
+++ b/Documentation/x86/x86_64/boot-options.txt
@@ -50,6 +50,11 @@ Machine check
monarchtimeout:
Sets the time in us to wait for other CPUs on machine checks. 0
to disable.
+ mce=bios_cmci_threshold
+ Don't overwrite the bios-set CMCI threshold. This boot option
+ prevents Linux from overwriting the CMCI threshold set by the
+ bios. Without this option, Linux always sets the CMCI
+ threshold to 1.

nomce (for compatibility with i386): same as mce=off

diff --git a/arch/x86/include/asm/mce.h b/arch/x86/include/asm/mce.h
index a3ac52b..8ad5078 100644
--- a/arch/x86/include/asm/mce.h
+++ b/arch/x86/include/asm/mce.h
@@ -171,6 +171,7 @@ DECLARE_PER_CPU(struct device *, mce_device);
#ifdef CONFIG_X86_MCE_INTEL
extern int mce_cmci_disabled;
extern int mce_ignore_ce;
+extern int mce_bios_cmci_threshold;
void mce_intel_feature_init(struct cpuinfo_x86 *c);
void cmci_clear(void);
void cmci_reenable(void);
diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
index c311122..29e87d3 100644
--- a/arch/x86/kernel/cpu/mcheck/mce.c
+++ b/arch/x86/kernel/cpu/mcheck/mce.c
@@ -83,6 +83,7 @@ static int mce_dont_log_ce __read_mostly;
int mce_cmci_disabled __read_mostly;
int mce_ignore_ce __read_mostly;
int mce_ser __read_mostly;
+int mce_bios_cmci_threshold __read_mostly;

struct mce_bank *mce_banks __read_mostly;

@@ -1946,6 +1947,7 @@ static struct miscdevice mce_chrdev_device = {
* check, or 0 to not wait
* mce=bootlog Log MCEs from before booting. Disabled by default on AMD.
* mce=nobootlog Don't log MCEs from before booting.
+ * mce=bios_cmci_threshold Don't program the CMCI threshold
*/
static int __init mcheck_enable(char *str)
{
@@ -1965,6 +1967,8 @@ static int __init mcheck_enable(char *str)
mce_ignore_ce = 1;
else if (!strcmp(str, "bootlog") || !strcmp(str, "nobootlog"))
mce_bootlog = (str[0] == 'b');
+ else if (!strcmp(str, "bios_cmci_threshold"))
+ mce_bios_cmci_threshold = 1;
else if (isdigit(str[0])) {
get_option(&str, &tolerant);
if (*str == ',') {
@@ -2205,6 +2209,11 @@ static struct dev_ext_attribute dev_attr_cmci_disabled = {
&mce_cmci_disabled
};

+static struct dev_ext_attribute dev_attr_bios_cmci_threshold = {
+ __ATTR(bios_cmci_threshold, 0444, device_show_int, NULL),
+ &mce_bios_cmci_threshold
+};
+
static struct device_attribute *mce_device_attrs[] = {
&dev_attr_tolerant.attr,
&dev_attr_check_interval.attr,
@@ -2213,6 +2222,7 @@ static struct device_attribute *mce_device_attrs[] = {
&dev_attr_dont_log_ce.attr,
&dev_attr_ignore_ce.attr,
&dev_attr_cmci_disabled.attr,
+ &dev_attr_bios_cmci_threshold.attr,
NULL
};

diff --git a/arch/x86/kernel/cpu/mcheck/mce_intel.c b/arch/x86/kernel/cpu/mcheck/mce_intel.c
index 098386f..5f88abf 100644
--- a/arch/x86/kernel/cpu/mcheck/mce_intel.c
+++ b/arch/x86/kernel/cpu/mcheck/mce_intel.c
@@ -181,10 +181,12 @@ static void cmci_discover(int banks)
unsigned long *owned = (void *)&__get_cpu_var(mce_banks_owned);
unsigned long flags;
int i;
+ int bios_wrong_thresh = 0;

raw_spin_lock_irqsave(&cmci_discover_lock, flags);
for (i = 0; i < banks; i++) {
u64 val;
+ int bios_zero_thresh = 0;

if (test_bit(i, owned))
continue;
@@ -198,8 +200,20 @@ static void cmci_discover(int banks)
continue;
}

- val &= ~MCI_CTL2_CMCI_THRESHOLD_MASK;
- val |= MCI_CTL2_CMCI_EN | CMCI_THRESHOLD;
+ if (!mce_bios_cmci_threshold) {
+ val &= ~MCI_CTL2_CMCI_THRESHOLD_MASK;
+ val |= CMCI_THRESHOLD;
+ } else if (!(val & MCI_CTL2_CMCI_THRESHOLD_MASK)) {
+ /*
+ * If bios_cmci_threshold boot option was specified
+ * but the threshold is zero, we'll try to initialize
+ * it to 1.
+ */
+ bios_zero_thresh = 1;
+ val |= CMCI_THRESHOLD;
+ }
+
+ val |= MCI_CTL2_CMCI_EN;
wrmsrl(MSR_IA32_MCx_CTL2(i), val);
rdmsrl(MSR_IA32_MCx_CTL2(i), val);

@@ -207,11 +221,26 @@ static void cmci_discover(int banks)
if (val & MCI_CTL2_CMCI_EN) {
set_bit(i, owned);
__clear_bit(i, __get_cpu_var(mce_poll_banks));
+ /*
+ * We are able to set thresholds for some banks that
+ * had a threshold of 0. This means the BIOS has not
+ * set the thresholds properly or does not work with
+ * this boot option. Note down now and report later.
+ */
+ if (mce_bios_cmci_threshold && bios_zero_thresh &&
+ (val & MCI_CTL2_CMCI_THRESHOLD_MASK))
+ bios_wrong_thresh = 1;
} else {
WARN_ON(!test_bit(i, __get_cpu_var(mce_poll_banks)));
}
}
raw_spin_unlock_irqrestore(&cmci_discover_lock, flags);
+ if (mce_bios_cmci_threshold && bios_wrong_thresh) {
+ pr_info_once(
+ "bios_cmci_threshold: Some banks do not have valid thresholds set\n");
+ pr_info_once(
+ "bios_cmci_threshold: Make sure your BIOS supports this boot option\n");
+ }
}

/*
@@ -249,7 +278,7 @@ void cmci_clear(void)
continue;
/* Disable CMCI */
rdmsrl(MSR_IA32_MCx_CTL2(i), val);
- val &= ~(MCI_CTL2_CMCI_EN|MCI_CTL2_CMCI_THRESHOLD_MASK);
+ val &= ~MCI_CTL2_CMCI_EN;
wrmsrl(MSR_IA32_MCx_CTL2(i), val);
__clear_bit(i, __get_cpu_var(mce_banks_owned));
}


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