powerpc: Activate CONFIG_STRICT_KERNEL_RWX by default
CONFIG_STRICT_KERNEL_RWX should be set by default on every architectures (See https://github.com/KSPP/linux/issues/4) On PPC32 we have to find a compromise between performance and/or memory wasting and selection of strict_kernel_rwx, because it implies either smaller memory chunks or larger alignment between RO memory and RW memory. For instance the 8xx maps memory with 8M pages. So either the limit between RO and RW must be 8M aligned or it falls back or 512k pages which implies more pressure on the TLB. book3s/32 maps memory with BATs as much as possible. BATS can have any power-of-two size between 128k and 256M but we have only 4 to 8 BATs so the alignment must be good enough to allow efficient use of the BATs and avoid falling back on standard page mapping which would kill performance. So let's go one step forward and make it the default but still allow users to unset it when wanted. Signed-off-by:Christophe Leroy <christophe.leroy@csgroup.eu> Signed-off-by:
Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/057c40164084bfc7d77c0b2ff78d95dbf6a2a21b.1632503622.git.christophe.leroy@csgroup.eu
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