How to enable CMA(Contiguous Memory Allocator）

I'm trying to enable CMA (Contituous Memory Allocator) in RHEL8.4.
When I confirm /usr/src/kernels/4.18.0-305.19.1.el8_4.x86_64/.config, ”CONFIG_CMA” is disabled by default.

#cat /usr/src/kernels/4.18.0-305.19.1.el8_4.x86_64/.config
...
#CONFIG_CMA is not set
...

I described ”CONFIG_CMA=y” and rebuilt the kernel, but an error as follows was output.

#cd /usr/src/kernels/4.18.0-305.19.1.el8_4.x86_64/
#make
...
Contiguous Memory Allocator (CMA) [Y/n/?] y
...
#
# configuration written to .config
#
HOSTCC arch/x86/tools/relocs_32.o
HOSTCC arch/x86/tools/relocs_64.o
HOSTCC arch/x86/tools/relocs_common.o
HOSTLD arch/x86/tools/relocs
DESCEND objtool
/usr/src/kernels/4.18.0-305.19.1.el8_4.x86_64/tools/build/Makefile.build:37: /usr/src/kernels/4.18.0-305.19.1.el8_4.x86_64/tools/build/Build.include: No such file or directory
make[4]: *** No rule to make target '/usr/src/kernels/4.18.0-305.19.1.el8_4.x86_64/tools/build/Build.include'. Stop.
make[3]: *** [Makefile:43: /usr/src/kernels/4.18.0-305.19.1.el8_4.x86_64/tools/objtool/fixdep-in.o] Error 2
make[2]: *** [/usr/src/kernels/4.18.0-305.19.1.el8_4.x86_64/tools/build/Makefile.include:4: fixdep] Error 2
make[1]: *** [Makefile:65: objtool] Error 2
make: *** [Makefile:1691: tools/objtool] Error 2

How can I enable the CMA?