x86/fault: #PF improvements, mostly related to USER bit

This series is a whole bunch of page fault cleanups, plus a couple of OOPS diagnostic improvements. The overall goals are to clean up handling of the faulting CPL, the USER bit in the error_code, and the log messages generated by #PF OOPSes.

This series can also be seen as CET preparation. CET introduces the WRUSS instruction, which is the very first way for CPL 0 code to cause a #PF fault with the USER bit set. Let's get the page fault code into shape before we start using WRUSS :)

Changes from v1:
- Rebase on top of tip:x86/mm, now that a bunch of v1 was applied. The only material changes are that 'x86/fault: Check user_mode(regs) when validating a stack extension' is gone because the code it fixed has been deleted and that 'x86/fault:
Remove sw_error_code' lost the hunk that changed the same code.

Andy Lutomirski (5):
x86/fault: Remove sw_error_code
x86/fault: Don't try to recover from an implicit supervisor access x86/oops: Show the correct CS value in show_regs() x86/fault: Decode page fault OOPSes better x86/vsyscall/64: Use X86_PF constants in the simulated #PF error code

 arch/x86/entry/vsyscall/vsyscall_64.c |   2 +-
 arch/x86/kernel/process_64.c          |   5 +-
 arch/x86/mm/fault.c                   | 144 +++++++++++++++++++-------
 3 files changed, 108 insertions(+), 43 deletions(-)

2.17.2