arm64: kdump: Try not to use NO_BLOCK_MAPPINGS for memory under 4G

hulk inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I545H8


CVE: NA

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For the case crashkernel=X@offset and crashkernel=X,high, we've explicitly
used 'crashk_res' to mark the scope of the page-level mapping required, so
NO_BLOCK_MAPPINGS should not be required for other areas. Otherwise,
system performance will be affected. In fact, only the case crashkernel=X
requires page-level mapping for all low memory under 4G because it
attempts high memory after it fails to request low memory first, and we
cannot predict its final location.

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Reviewed-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>