[tip:x86/fpu] x86/fpu: Make the fpu state change in fpu__clear() scheduler-atomic

[tip-bot for Ingo Molnar]

Commit-ID:  a10b6a16cdad88170f546d008c77453cddf918e6
Gitweb:     http://git.kernel.org/tip/a10b6a16cdad88170f546d008c77453cddf918e6
Author:     Ingo Molnar <mingo@xxxxxxxxxx>
AuthorDate: Sat, 23 Sep 2017 14:59:59 +0200
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Sun, 24 Sep 2017 13:04:33 +0200

x86/fpu: Make the fpu state change in fpu__clear() scheduler-atomic

Do this temporarily only, to make it easier to change the FPU state machine,
in particular this change couples the fpu->fpregs_active and fpu->fpstate_active
states: they are only set/cleared together (as far as the scheduler sees them).

This will be removed by later patches.

Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Eric Biggers <ebiggers3@xxxxxxxxx>
Cc: Fenghua Yu <fenghua.yu@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx>
Link: http://lkml.kernel.org/r/20170923130016.21448-17-mingo@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 arch/x86/kernel/fpu/core.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index bad5724..b7dc383 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -462,9 +462,11 @@ void fpu__clear(struct fpu *fpu)
 	 * Make sure fpstate is cleared and initialized.
 	 */
 	if (static_cpu_has(X86_FEATURE_FPU)) {
+		preempt_disable();
 		fpu__activate_curr(fpu);
 		user_fpu_begin();
 		copy_init_fpstate_to_fpregs();
+		preempt_enable();
 	}
 }