The later verions of the KAISER pathces (pre-PTI) allowed the user/kernel shared areas to be GLOBAL. The thought was that this would reduce the TLB overhead of keeping two copies of these mappings. During the switch over to PTI, we seem to have lost our ability to have GLOBAL mappings. This adds them back. This adds one major change from the last version of the patch set (present in the last patch). It makes all kernel text global for non- PCID systems. This keeps kernel data protected always, but means that it will be easier to find kernel gadgets via meltdown on old systems without PCIDs. This heuristic is, I think, a reasonable one and it keeps us from having to create any new pti=foo options Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx> Cc: Andy Lutomirski <luto@xxxxxxxxxx> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Cc: Kees Cook <keescook@xxxxxxxxxx> Cc: Hugh Dickins <hughd@xxxxxxxxxx> Cc: Juergen Gross <jgross@xxxxxxxx> Cc: x86@xxxxxxxxxx Cc: Nadav Amit <namit@xxxxxxxxxx>
