// SPDX-License-Identifier: GPL-2.0
#include <linux/mm.h>
#include <linux/gfp.h>
#include <linux/kernel.h>
#include <asm/mce.h>
#include "debugfs.h"
/*
* RAS Correctable Errors Collector
*
* This is a simple gadget which collects correctable errors and counts their
* occurrence per physical page address.
*
* We've opted for possibly the simplest data structure to collect those - an
* array of the size of a memory page. It stores 512 u64's with the following
* structure:
*
* [63 ... PFN ... 12 | 11 ... generation ... 10 | 9 ... count ... 0]
*
* The generation in the two highest order bits is two bits which are set to 11b
* on every insertion. During the course of each entry's existence, the
* generation field gets decremented during spring cleaning to 10b, then 01b and
* then 00b.
*
* This way we're employing the natural numeric ordering to make sure that newly
* inserted/touched elements have higher 12-bit counts (which we've manufactured)
* and thus iterating over the array initially won't kick out those elements
* which were inserted last.
*
* Spring cleaning is what we do when we reach a certain number CLEAN_ELEMS of
* elements entered into the array, during which, we're decaying all elements.
* If, after decay, an element gets inserted again, its generation is set to 11b
* to make sure it has higher numerical count than other, older elements and
* thus emulate an an LRU-like behavior when deleting elements to free up space
* in the page.
*
* When an element reaches it's max count of count_threshold, we try to poison
* it by assuming that errors triggered count_threshold times in a single page
* are excessive and that page shouldn't be used anymore. count_threshold is
* initialized to COUNT_MASK which is the maximum.
*
* That error event entry causes cec_add_elem() to return !0 value and thus
* signal to its callers to log the error.
*
* To the question why we've chosen a page and moving elements around with
* memmove(), it is because it is a very simple structure to handle and max data
* movement is 4K which on highly optimized modern CPUs is almost unnoticeable.
* We wanted to avoid the pointer traversal of more complex structures like a
* linked list or some sort of a balancing search tree.
*
* Deleting an element takes O(n) but since it is only a single page, it should
* be fast enough and it shouldn't happen all too often depending on error
* patterns.
*/
#undef pr_fmt
#define pr_fmt(fmt) "RAS: " fmt
/*
* We use DECAY_BITS bits of PAGE_SHIFT bits for counting decay, i.e., how long
* elements have stayed in the array without having been accessed again.
*/
#define DECAY_BITS 2
#define DECAY_MASK ((1ULL << DECAY_BITS) - 1)
#define MAX_ELEMS (PAGE_SIZE / sizeof(u64))
/*
* Threshold amount of inserted elements after which we start spring
* cleaning.
*/
#define CLEAN_ELEMS (MAX_ELEMS >> DECAY_BITS)
/* Bits which count the number of errors happened in this 4K page. */
#define COUNT_BITS (PAGE_SHIFT - DECAY_BITS)
#define COUNT_MASK ((1ULL << COUNT_BITS) - 1)
#define FULL_COUNT_MASK (PAGE_SIZE - 1)
/*
* u64: [ 63 ... 12 | DECAY_BITS | COUNT_BITS ]
*/
#define PFN(e) ((e) >> PAGE_SHIFT)
#define DECAY(e) (((e) >> COUNT_BITS) & DECAY_MASK)
#define COUNT(e) ((unsigned int)(e) & COUNT_MASK)
#define FULL_COUNT(e) ((e) & (PAGE_SIZE - 1))
static struct ce_array {
u64 *array; /* container page */
unsigned int n; /* number of elements in the array */
unsigned int decay_count; /*
* number of element insertions/increments
* since the last spring cleaning.
*/
u64 pfns_poisoned; /*
* number of PFNs which got poisoned.
*/
u64 ces_entered; /*
* The number of correctable errors
* entered into the collector.
*/
u64 decays_done; /*
* Times we did spring cleaning.
*/
union {
struct {
__u32 disabled : 1, /* cmdline disabled */
__resv : 31;
};
__u32 flags;
};
} 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;
/*
* The timer "decays" element count each timer_interval which is 24hrs by
* default.
*/
#define CEC_TIMER_DEFAULT_INTERVAL 24 * 60 * 60 /* 24 hrs */
#define CEC_TIMER_MIN_INTERVAL 1 * 60 * 60 /* 1h */
#define CEC_TIMER_MAX_INTERVAL 30 * 24 * 60 * 60 /* one month */
static struct timer_list cec_timer;
static u64 timer_interval = CEC_TIMER_DEFAULT_INTERVAL;
/*
* Decrement decay value. We're using DECAY_BITS bits to denote decay of an
* element in the array. On insertion and any access, it gets reset to max.
*/
static void do_spring_cleaning(struct ce_array *ca)
{
int i;
for (i = 0; i < ca->n; i++) {
u8 decay = DECAY(ca->array[i]);
if (!decay)
continue;
decay--;
ca->array[i] &= ~(DECAY_MASK << COUNT_BITS);
ca->array[i] |= (decay << COUNT_BITS);
}
ca->decay_count = 0;
ca->decays_done++;
}
/*
* @interval in seconds
*/
static void cec_mod_timer(struct timer_list *t, unsigned long interval)
{
unsigned long iv;
iv = interval * HZ + jiffies;
mod_timer(t, round_jiffies(iv));
}
static void cec_timer_fn(struct timer_list *unused)
{
do_spring_cleaning(&ce_arr);
cec_mod_timer(&cec_timer, timer_interval);
}
/*
* @to: index of the smallest element which is >= then @pfn.
*
* Return the index of the pfn if found, otherwise negative value.
*/
static int __find_elem(struct ce_array *ca, u64 pfn, unsigned int *to)
{
u64 this_pfn;
int min = 0, max = ca->n;
while (min < max) {
int tmp = (max + min) >> 1;
this_pfn = PFN(ca->array[tmp]);
if (this_pfn < pfn)
min = tmp + 1;
else if (this_pfn > pfn)
max = tmp;
else {
min = tmp;
break;
}
}
if (to)
*to = min;
this_pfn = PFN(ca->array[min]);
if (this_pfn == pfn)
return min;
return -ENOKEY;
}
static int find_elem(struct ce_array *ca, u64 pfn, unsigned int *to)
{
WARN_ON(!to);
if (!ca->n) {
*to = 0;
return -ENOKEY;
}
return __find_elem(ca, pfn, to);
}
static void del_elem(struct ce_array *ca, int idx)
{
/* Save us a function call when deleting the last element. */
if (ca->n - (idx + 1))
memmove((void *)&ca->array[idx],
(void *)&ca->array[idx + 1],
(ca->n - (idx + 1)) * sizeof(u64));
ca->n--;
}
static u64 del_lru_elem_unlocked(struct ce_array *ca)
{
unsigned int min = FULL_COUNT_MASK;
int i, min_idx = 0;
for (i = 0; i < ca->n; i++) {
unsigned int this = FULL_COUNT(ca->array[i]);
if (min > this) {
min = this;
min_idx = i;
}
}
del_elem(ca, min_idx);
return PFN(ca->array[min_idx]);
}
/*
* We return the 0th pfn in the error case under the assumption that it cannot
* be poisoned and excessive CEs in there are a serious deal anyway.
*/
static u64 __maybe_unused del_lru_elem(void)
{
struct ce_array *ca = &ce_arr;
u64 pfn;
if (!ca->n)
return 0;
mutex_lock(&ce_mutex);
pfn = del_lru_elem_unlocked(ca);
mutex_unlock(&ce_mutex);
return pfn;
}
int cec_add_elem(u64 pfn)
{
struct ce_array *ca = &ce_arr;
unsigned int to;
int count, ret = 0;
/*
* We can be called very early on the identify_cpu() path where we are
* not initialized yet. We ignore the error for simplicity.
*/
if (!ce_arr.array || ce_arr.disabled)
return -ENODEV;
ca->ces_entered++;
mutex_lock(&ce_mutex);
if (ca->n == MAX_ELEMS)
WARN_ON(!del_lru_elem_unlocked(ca));
ret = find_elem(ca, pfn, &to);
if (ret < 0) {
/*
* Shift range [to-end] to make room for one more element.
*/
memmove((void *)&ca->array[to + 1],
(void *)&ca->array[to],
(ca->n - to) * sizeof(u64));
ca->array[to] = (pfn << PAGE_SHIFT) |
(DECAY_MASK << COUNT_BITS) | 1;
ca->n++;
ret = 0;
goto decay;
}
count = COUNT(ca->array[to]);
if (count < count_threshold) {
ca->array[to] |= (DECAY_MASK << COUNT_BITS);
ca->array[to]++;
ret = 0;
} else {
u64 pfn = ca->array[to] >> PAGE_SHIFT;
if (!pfn_valid(pfn)) {
pr_warn("CEC: Invalid pfn: 0x%llx\n", pfn);
} else {
/* We have reached max count for this page, soft-offline it. */
pr_err("Soft-offlining pfn: 0x%llx\n", pfn);
memory_failure_queue(pfn, MF_SOFT_OFFLINE);
ca->pfns_poisoned++;
}
del_elem(ca, to);
/*
* Return a >0 value to denote that we've reached the offlining
* threshold.
*/
ret = 1;
goto unlock;
}
decay:
ca->decay_count++;
if (ca->decay_count >= CLEAN_ELEMS)
do_spring_cleaning(ca);
unlock:
mutex_unlock(&ce_mutex);
return ret;
}
static int u64_get(void *data, u64 *val)
{
*val = *(u64 *)data;
return 0;
}
static int pfn_set(void *data, u64 val)
{
*(u64 *)data = val;
return cec_add_elem(val);
}
DEFINE_DEBUGFS_ATTRIBUTE(pfn_ops, u64_get, pfn_set, "0x%llx\n");
static int decay_interval_set(void *data, u64 val)
{
*(u64 *)data = val;
if (val < CEC_TIMER_MIN_INTERVAL)
return -EINVAL;
if (val > CEC_TIMER_MAX_INTERVAL)
return -EINVAL;
timer_interval = val;
cec_mod_timer(&cec_timer, timer_interval);
return 0;
}
DEFINE_DEBUGFS_ATTRIBUTE(decay_interval_ops, u64_get, decay_interval_set, "%lld\n");
static int count_threshold_set(void *data, u64 val)
{
*(u64 *)data = val;
if (val > COUNT_MASK)
val = COUNT_MASK;
count_threshold = val;
return 0;
}
DEFINE_DEBUGFS_ATTRIBUTE(count_threshold_ops, u64_get, count_threshold_set, "%lld\n");
static int array_dump(struct seq_file *m, void *v)
{
struct ce_array *ca = &ce_arr;
u64 prev = 0;
int i;
mutex_lock(&ce_mutex);
seq_printf(m, "{ n: %d\n", ca->n);
for (i = 0; i < ca->n; i++) {
u64 this = PFN(ca->array[i]);
seq_printf(m, " %03d: [%016llx|%03llx]\n", i, this, FULL_COUNT(ca->array[i]));
WARN_ON(prev > this);
prev = this;
}
seq_printf(m, "}\n");
seq_printf(m, "Stats:\nCEs: %llu\nofflined pages: %llu\n",
ca->ces_entered, ca->pfns_poisoned);
seq_printf(m, "Flags: 0x%x\n", ca->flags);
seq_printf(m, "Timer interval: %lld seconds\n", timer_interval);
seq_printf(m, "Decays: %lld\n", ca->decays_done);
seq_printf(m, "Action threshold: %d\n", count_threshold);
mutex_unlock(&ce_mutex);
return 0;
}
static int array_open(struct inode *inode, struct file *filp)
{
return single_open(filp, array_dump, NULL);
}
static const struct file_operations array_ops = {
.owner = THIS_MODULE,
.open = array_open,
.read = seq_read,
.llseek = seq_lseek,
.release = single_release,
};
static int __init create_debugfs_nodes(void)
{
struct dentry *d, *pfn, *decay, *count, *array;
d = debugfs_create_dir("cec", ras_debugfs_dir);
if (!d) {
pr_warn("Error creating cec debugfs node!\n");
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");
goto err;
}
array = debugfs_create_file("array", S_IRUSR, d, NULL, &array_ops);
if (!array) {
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);
if (!decay) {
pr_warn("Error creating decay_interval debugfs node!\n");
goto err;
}
count = debugfs_create_file("count_threshold", S_IRUSR | S_IWUSR, d,
&count_threshold, &count_threshold_ops);
if (!count) {
pr_warn("Error creating count_threshold debugfs node!\n");
goto err;
}
return 0;
err:
debugfs_remove_recursive(d);
return 1;
}
void __init cec_init(void)
{
if (ce_arr.disabled)
return;
ce_arr.array = (void *)get_zeroed_page(GFP_KERNEL);
if (!ce_arr.array) {
pr_err("Error allocating CE array page!\n");
return;
}
if (create_debugfs_nodes())
return;
timer_setup(&cec_timer, cec_timer_fn, 0);
cec_mod_timer(&cec_timer, CEC_TIMER_DEFAULT_INTERVAL);
pr_info("Correctable Errors collector initialized.\n");
}
int __init parse_cec_param(char *str)
{
if (!str)
return 0;
if (*str == '=')
str++;
if (!strcmp(str, "cec_disable"))
ce_arr.disabled = 1;
else
return 0;
return 1;
}
