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, 2 insertions, 2 deletions

diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c
index 3df0cfae535f..cd6eafba12da 100644
--- a/arch/x86/kernel/fpu/signal.c
+++ b/arch/x86/kernel/fpu/signal.c
@@ -289,7 +289,7 @@ static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size)
 			 IS_ENABLED(CONFIG_IA32_EMULATION));
 
 	if (!buf) {
-		fpu__clear(fpu);
+		fpu__clear_user_states(fpu);
 		return 0;
 	}
 
@@ -416,7 +416,7 @@ static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size)
 
 err_out:
 	if (ret)
-		fpu__clear(fpu);
+		fpu__clear_user_states(fpu);
 	return ret;
 }