check.c

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#include <linux/module.h>
#include <linux/sched.h>
#include <linux/kthread.h>
#include <linux/workqueue.h>
#include <linux/memblock.h>

#include <asm/proto.h>

/*
 * Some BIOSes seem to corrupt the low 64k of memory during events
 * like suspend/resume and unplugging an HDMI cable.  Reserve all
 * remaining free memory in that area and fill it with a distinct
 * pattern.
 */
#define MAX_SCAN_AREAS  8

static int __read_mostly memory_corruption_check = -1;

static unsigned __read_mostly corruption_check_size = 64*1024;
static unsigned __read_mostly corruption_check_period = 60; /* seconds */

static struct scan_area {
    u64 addr;
    u64 size;
} scan_areas[MAX_SCAN_AREAS];
static int num_scan_areas;

static __init int set_corruption_check(char *arg)
{
    ssize_t ret;
    unsigned long val;

    ret = kstrtoul(arg, 10, &val);
    if (ret)
        return ret;

    memory_corruption_check = val;
    return 0;
}
early_param("memory_corruption_check", set_corruption_check);

static __init int set_corruption_check_period(char *arg)
{
    ssize_t ret;
    unsigned long val;

    ret = kstrtoul(arg, 10, &val);
    if (ret)
        return ret;

    corruption_check_period = val;
    return 0;
}
early_param("memory_corruption_check_period", set_corruption_check_period);

static __init int set_corruption_check_size(char *arg)
{
    char *end;
    unsigned size;

    size = memparse(arg, &end);

    if (*end == '\0')
        corruption_check_size = size;

    return (size == corruption_check_size) ? 0 : -EINVAL;
}
early_param("memory_corruption_check_size", set_corruption_check_size);


void __init setup_bios_corruption_check(void)
{
    phys_addr_t start, end;
    u64 i;

    if (memory_corruption_check == -1) {
        memory_corruption_check =
#ifdef CONFIG_X86_BOOTPARAM_MEMORY_CORRUPTION_CHECK
            1
#else
            0
#endif
            ;
    }

    if (corruption_check_size == 0)
        memory_corruption_check = 0;

    if (!memory_corruption_check)
        return;

    corruption_check_size = round_up(corruption_check_size, PAGE_SIZE);

    for_each_free_mem_range(i, MAX_NUMNODES, &start, &end, NULL) {
        start = clamp_t(phys_addr_t, round_up(start, PAGE_SIZE),
                PAGE_SIZE, corruption_check_size);
        end = clamp_t(phys_addr_t, round_down(end, PAGE_SIZE),
                  PAGE_SIZE, corruption_check_size);
        if (start >= end)
            continue;

        memblock_reserve(start, end - start);
        scan_areas[num_scan_areas].addr = start;
        scan_areas[num_scan_areas].size = end - start;

        /* Assume we've already mapped this early memory */
        memset(__va(start), 0, end - start);

        if (++num_scan_areas >= MAX_SCAN_AREAS)
            break;
    }

    if (num_scan_areas)
        printk(KERN_INFO "Scanning %d areas for low memory corruption\n", num_scan_areas);
}


void check_for_bios_corruption(void)
{
    int i;
    int corruption = 0;

    if (!memory_corruption_check)
        return;

    for (i = 0; i < num_scan_areas; i++) {
        unsigned long *addr = __va(scan_areas[i].addr);
        unsigned long size = scan_areas[i].size;

        for (; size; addr++, size -= sizeof(unsigned long)) {
            if (!*addr)
                continue;
            printk(KERN_ERR "Corrupted low memory at %p (%lx phys) = %08lx\n",
                   addr, __pa(addr), *addr);
            corruption = 1;
            *addr = 0;
        }
    }

    WARN_ONCE(corruption, KERN_ERR "Memory corruption detected in low memory\n");
}

static void check_corruption(struct work_struct *dummy);
static DECLARE_DELAYED_WORK(bios_check_work, check_corruption);

static void check_corruption(struct work_struct *dummy)
{
    check_for_bios_corruption();
    schedule_delayed_work(&bios_check_work,
        round_jiffies_relative(corruption_check_period*HZ));
}

static int start_periodic_check_for_corruption(void)
{
    if (!num_scan_areas || !memory_corruption_check || corruption_check_period == 0)
        return 0;

    printk(KERN_INFO "Scanning for low memory corruption every %d seconds\n",
           corruption_check_period);

    /* First time we run the checks right away */
    schedule_delayed_work(&bios_check_work, 0);
    return 0;
}

module_init(start_periodic_check_for_corruption);