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    #include <linux/kernel.h>
    #include <linux/types.h>
    #include <linux/init.h>
    #include <linux/memblock.h>
    
    static u64 patterns[] __initdata = {
    	/* The first entry has to be 0 to leave memtest with zeroed memory */
    	0,
    	0xffffffffffffffffULL,
    	0x5555555555555555ULL,
    	0xaaaaaaaaaaaaaaaaULL,
    	0x1111111111111111ULL,
    	0x2222222222222222ULL,
    	0x4444444444444444ULL,
    	0x8888888888888888ULL,
    	0x3333333333333333ULL,
    	0x6666666666666666ULL,
    	0x9999999999999999ULL,
    	0xccccccccccccccccULL,
    	0x7777777777777777ULL,
    	0xbbbbbbbbbbbbbbbbULL,
    	0xddddddddddddddddULL,
    	0xeeeeeeeeeeeeeeeeULL,
    	0x7a6c7258554e494cULL, /* yeah ;-) */
    };
    
    static void __init reserve_bad_mem(u64 pattern, phys_addr_t start_bad, phys_addr_t end_bad)
    {
    	pr_info("  %016llx bad mem addr %pa - %pa reserved\n",
    		cpu_to_be64(pattern), &start_bad, &end_bad);
    	memblock_reserve(start_bad, end_bad - start_bad);
    }
    
    static void __init memtest(u64 pattern, phys_addr_t start_phys, phys_addr_t size)
    {
    	u64 *p, *start, *end;
    	phys_addr_t start_bad, last_bad;
    	phys_addr_t start_phys_aligned;
    	const size_t incr = sizeof(pattern);
    
    	start_phys_aligned = ALIGN(start_phys, incr);
    	start = __va(start_phys_aligned);
    	end = start + (size - (start_phys_aligned - start_phys)) / incr;
    	start_bad = 0;
    	last_bad = 0;
    
    	for (p = start; p < end; p++)
    		*p = pattern;
    
    	for (p = start; p < end; p++, start_phys_aligned += incr) {
    		if (*p == pattern)
    			continue;
    		if (start_phys_aligned == last_bad + incr) {
    			last_bad += incr;
    			continue;
    		}
    		if (start_bad)
    			reserve_bad_mem(pattern, start_bad, last_bad + incr);
    		start_bad = last_bad = start_phys_aligned;
    	}
    	if (start_bad)
    		reserve_bad_mem(pattern, start_bad, last_bad + incr);
    }
    
    static void __init do_one_pass(u64 pattern, phys_addr_t start, phys_addr_t end)
    {
    	u64 i;
    	phys_addr_t this_start, this_end;
    
    	for_each_free_mem_range(i, NUMA_NO_NODE, MEMBLOCK_NONE, &this_start,
    				&this_end, NULL) {
    		this_start = clamp(this_start, start, end);
    		this_end = clamp(this_end, start, end);
    		if (this_start < this_end) {
    			pr_info("  %pa - %pa pattern %016llx\n",
    				&this_start, &this_end, cpu_to_be64(pattern));
    			memtest(pattern, this_start, this_end - this_start);
    		}
    	}
    }
    
    /* default is disabled */
    static unsigned int memtest_pattern __initdata;
    
    static int __init parse_memtest(char *arg)
    {
    	int ret = 0;
    
    	if (arg)
    		ret = kstrtouint(arg, 0, &memtest_pattern);
    	else
    		memtest_pattern = ARRAY_SIZE(patterns);
    
    	return ret;
    }
    
    early_param("memtest", parse_memtest);
    
    void __init early_memtest(phys_addr_t start, phys_addr_t end)
    {
    	unsigned int i;
    	unsigned int idx = 0;
    
    	if (!memtest_pattern)
    		return;
    
    	pr_info("early_memtest: # of tests: %u\n", memtest_pattern);
    	for (i = memtest_pattern-1; i < UINT_MAX; --i) {
    		idx = i % ARRAY_SIZE(patterns);
    		do_one_pass(patterns[idx], start, end);
    	}
    }