There's even official hardware support for doing that. ARM calls it Top Byte Ignore, it's supported on all 64-bit ARM CPUs, and it's been enabled on Linux for

There's even official hardware support for doing that. ARM calls it Top Byte Ignore, it's supported on all 64-bit ARM CPUs, and it's been enabled on Linux for a long time (see https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/arm64/tagged-pointers.rst?h=v5.19 https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/lin... and https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/arm64/tagged-address-abi.rst?h=v5.19 https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/lin...). Intel calls it Linear Address Masking and AMD calls it Upper Address Ignore, however these will be available only on very recent hardware, and the Linux patches for them are still under development (see https://lwn.net/Articles/902094/ https://lwn.net/Articles/902094/ and https://lwn.net/Articles/888914/ https://lwn.net/Articles/888914/).