x86/fpu/xstate: Define new functions for clearing fpregs and xstates

Currently, fpu__clear() clears all fpregs and xstates.  Once XSAVES
supervisor states are introduced, supervisor settings (e.g. CET xstates)
must remain active for signals; It is necessary to have separate functions:

- Create fpu__clear_user_states(): clear only user settings for signals;
- Create fpu__clear_all(): clear both user and supervisor settings in
   flush_thread().

Also modify copy_init_fpstate_to_fpregs() to take a mask from above two
functions.

Remove obvious side-comment in fpu__clear(), while at it.

 [ bp: Make the second argument of fpu__clear() bool after requesting it
   a bunch of times during review.
  - Add a comment about copy_init_fpstate_to_fpregs() locking needs. ]

Co-developed-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Link: https://lkml.kernel.org/r/20200512145444.15483-6-yu-cheng.yu@intel.com

1 files changed, 1 insertions, 1 deletions

diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c
index 83b74fb38c8f..0052bbe5dfd4 100644
--- a/arch/x86/kernel/signal.c
+++ b/arch/x86/kernel/signal.c
@@ -732,7 +732,7 @@ handle_signal(struct ksignal *ksig, struct pt_regs *regs)
 		/*
 		 * Ensure the signal handler starts with the new fpu state.
 		 */
-		fpu__clear(fpu);
+		fpu__clear_user_states(fpu);
 	}
 	signal_setup_done(failed, ksig, stepping);
 }