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SubjectRe: [PATCH v3 04/12] ppc64/kexec_file: avoid stomping memory used by special regions
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On 15/07/20 8:09 am, Thiago Jung Bauermann wrote:
>
> Hari Bathini <hbathini@linux.ibm.com> writes:
>

<snip>

>> +/**
>> + * __locate_mem_hole_top_down - Looks top down for a large enough memory hole
>> + * in the memory regions between buf_min & buf_max
>> + * for the buffer. If found, sets kbuf->mem.
>> + * @kbuf: Buffer contents and memory parameters.
>> + * @buf_min: Minimum address for the buffer.
>> + * @buf_max: Maximum address for the buffer.
>> + *
>> + * Returns 0 on success, negative errno on error.
>> + */
>> +static int __locate_mem_hole_top_down(struct kexec_buf *kbuf,
>> + u64 buf_min, u64 buf_max)
>> +{
>> + int ret = -EADDRNOTAVAIL;
>> + phys_addr_t start, end;
>> + u64 i;
>> +
>> + for_each_mem_range_rev(i, &memblock.memory, NULL, NUMA_NO_NODE,
>> + MEMBLOCK_NONE, &start, &end, NULL) {
>> + if (start > buf_max)
>> + continue;
>> +
>> + /* Memory hole not found */
>> + if (end < buf_min)
>> + break;
>> +
>> + /* Adjust memory region based on the given range */
>> + if (start < buf_min)
>> + start = buf_min;
>> + if (end > buf_max)
>> + end = buf_max;
>> +
>> + start = ALIGN(start, kbuf->buf_align);
>> + if (start < end && (end - start + 1) >= kbuf->memsz) {
>
> This is why I dislike using start and end to express address ranges:
>
> While struct resource seems to use the [address, end] convention, my

struct crash_mem also uses [address, end] convention.
This off-by-one error did not cause any issues as the hole start and size we try to find
are at least page aligned.

Nonetheless, I think fixing 'end' early in the loop with "end -= 1" would ensure
correctness while continuing to use the same convention for structs crash_mem & resource.

Thanks
Hari

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