During the investigation on JDK-8356020, it was found that CDS got a reserved memory base address different from reported by NMT. The problem was only seen on the linux-aarch64 platform.

$ ./jdk-25/fastdebug/bin/java -Xshare:dump -Xlog:cds -Xlog:nmt*=debug
[...]
[1.013s][debug ][nmt ] Add reserved region 'Shared class space' (0x0000fffef3bed000, 1073807360)
[1.013s][info ][cds ] Reserved output buffer space at 0x0000fffef3bf0000 [1073741824 bytes]

CDS got the base address of 0x0000fffef3bf0000, but for some reasons NMT thinks the address starts at 0x0000fffef3bed000

Note: this doesn't always happen. The mismatch happens only when the lowest bits of "Reserved output buffer space" are not (16KB or 48KB) aligned. Normally, you see well-aligned regions like the following and the bug is not triggered:

[1.395s][debug][nmt] Add reserved region 'Shared class space' (0x0000fffe48000000, 1073741824)
[1.395s][info ][cds] Reserved output buffer space at 0x0000fffe48000000 [1073741824 bytes]