ref: 128ea44a89c7905612ad2fa5a61a9325ddfb5e1e
parent: 91a8d03040a3533e27f51d33bbbfed33d84b5043
author: cinap_lenrek <cinap_lenrek@felloff.net>
date: Mon Aug 26 18:34:38 EDT 2019
kernel: expose no execute bit to portable mmu code as SG_NOEXEC / PTENOEXEC, add PTECACHED bits a portable SG_NOEXEC segment attribute was added to allow non-executable (physical) segments. which will set the PTENOEXEC bits for putmmu(). in the future, this can be used to make non-executable stack / bss segments. the SG_DEVICE attribute was added to distinguish between mmio regions and uncached memory. only matterns on arm64. on arm, theres the issue that PTEUNCACHED would have no bits set when using the hardware bit definitions. this is the reason bcm, kw, teg2 and omap kernels use arteficial PTE constants. on zynq, the XN bit was used as a hack to give PTEUNCACHED a non-zero value and when the bit is clear then cache attributes where added to the pte. to fix this, PTECACHED constant was added. the portable mmu code in fault.c will now explicitely set PTECACHED bits for cached memory and PTEUNCACHED for uncached memory. that way the hardware bit definitions can be used everywhere.