Backport 353d7a84c214f18 ("powerpc/64s/radix/kfence: map __kfence_pool at page granularity") to stable versions 6.1 and 6.6

Hi stable maintainers,

Please consider backporting upstream commit 353d7a84c214f184d5a6b62acdec8b4424159b7c ("powerpc/64s/radix/kfence: map __kfence_pool at page granularity")  to the stable 6.1 and 6.6 kernels.

This should be backported because it restores the intended KFENCE behaviour on powerpc64 radix MMU by limiting page-granular mappings to the KFENCE pool, rather than all system memory.

This commit appeared upstream in v6.11-rc1, and fixes an issue introduced by a5edf9815dd7 ("powerpc/64s: Enable KFENCE on book3s64") but it is not backported to stable versions.

The patch applies cleanly to both 6.1 and 6.6 stable versions.

Thanks, Aboorva