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Diffstat (limited to '')
| -rw-r--r-- | drivers/ras/cec.c | 537 |
1 files changed, 537 insertions, 0 deletions
diff --git a/drivers/ras/cec.c b/drivers/ras/cec.c new file mode 100644 index 000000000..5d2b2c02c --- /dev/null +++ b/drivers/ras/cec.c @@ -0,0 +1,537 @@ +// SPDX-License-Identifier: GPL-2.0 +#include <linux/mm.h> +#include <linux/gfp.h> +#include <linux/kernel.h> +#include <linux/workqueue.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; + +/* Each element "decays" each decay_interval which is 24hrs by default. */ +#define CEC_DECAY_DEFAULT_INTERVAL 24 * 60 * 60 /* 24 hrs */ +#define CEC_DECAY_MIN_INTERVAL 1 * 60 * 60 /* 1h */ +#define CEC_DECAY_MAX_INTERVAL 30 * 24 * 60 * 60 /* one month */ +static struct delayed_work cec_work; +static u64 decay_interval = CEC_DECAY_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_work(unsigned long interval) +{ + unsigned long iv; + + iv = interval * HZ; + mod_delayed_work(system_wq, &cec_work, round_jiffies(iv)); +} + +static void cec_work_fn(struct work_struct *work) +{ + mutex_lock(&ce_mutex); + do_spring_cleaning(&ce_arr); + mutex_unlock(&ce_mutex); + + cec_mod_work(decay_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) +{ + int min = 0, max = ca->n - 1; + u64 this_pfn; + + while (min <= max) { + int i = (min + max) >> 1; + + this_pfn = PFN(ca->array[i]); + + if (this_pfn < pfn) + min = i + 1; + else if (this_pfn > pfn) + max = i - 1; + else if (this_pfn == pfn) { + if (to) + *to = i; + + return i; + } + } + + /* + * When the loop terminates without finding @pfn, min has the index of + * the element slot where the new @pfn should be inserted. The loop + * terminates when min > max, which means the min index points to the + * bigger element while the max index to the smaller element, in-between + * which the new @pfn belongs to. + * + * For more details, see exercise 1, Section 6.2.1 in TAOCP, vol. 3. + */ + if (to) + *to = 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; + + cec_add_elem(val); + + return 0; +} + +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_DECAY_MIN_INTERVAL) + return -EINVAL; + + if (val > CEC_DECAY_MAX_INTERVAL) + return -EINVAL; + + decay_interval = val; + + cec_mod_work(decay_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, "Decay interval: %lld seconds\n", decay_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, + &decay_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; + + INIT_DELAYED_WORK(&cec_work, cec_work_fn); + schedule_delayed_work(&cec_work, CEC_DECAY_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; +} |