On Mon, Mar 25, 2019 at 09:46:59PM +0530, Anup Patel wrote: > > Why do you even care about kernel mappings for non-existant ram. > > We care because there will always be some buggy kernel driver/code going > out-of-bound and accessing non-existent RAM. If we by default map all > possible kernel virtual address then behaviour of buggy accesses will be > unpredictable. > > Further, I think we should also make .text and .rodata sections of kernel > as read-only. This will protect kernel code and rodata.
All of that is useful at the final_setup_vm() time - but none of it matters during early setup_vm where life is complicated. Mike suggested on the previous iteration that you only do smaller mappings when setting up the final mapping to avoid the ops churn, and I fully agree with him. So I would suggest we avoid complicated the fiddly early boot changes that just add complxity, and you instead redirect your efforts to say implemented proper ro and non-executable sections using 4k mappings in the final VM setup only. That should actuall lead to less code and complexity, and provide more benefits.
