Utilize ASIDs to reduce both the direct and indirect costs of context switching. The indirect costs being unnecessary TLB misses that are incurred when ASIDs are not used. In fact, currently, when we perform a context switch on one processor, we issue a broadcast TLB invalidation that flushes the TLB contents on every processor.
Mark all user-space ("ttbr0") page table entries with the non-global flag so that they are cached in the TLB under their ASID.
Correct an error in pmap_pinit0(). The pointer to the root of the page table was being initialized to the root of the kernel-space page table rather than a user-space page table. However, the root of the page table that was being cached in process 0's md_l0addr field correctly pointed to a user-space page table. As long as ASIDs weren't being used, this was harmless, except that it led to some unnecessary page table switches in pmap_switch(). Specifically, other kernel processes besides process 0 would have their md_l0addr field set to the root of the kernel-space page table, and so pmap_switch() would actually change page tables when switching between process 0 and other kernel processes.
Implement a workaround for Cavium erratum 27456 affecting ThunderX machines. (I would like to thank andrew@ for providing the code to detect the affected machines.)
Address integer overflow in the definition of TCR_ASID_16.
Setup TCR according to the PARange and ASIDBits fields from ID_AA64MMFR0_EL1. Previously, TCR_ASID_16 was unconditionally set.
Modify build_l1_block_pagetable so that lower attributes, such as ATTR_nG, can be specified.
Eliminate some unused code.