[tip:x86/fpu] x86/fpu: Introduce task_disable_lazy_fpu_restore() helper

[tip-bot for Rik van Riel]

Commit-ID:  33e03dedd759cc9396252d9641b25d01909a26bb
Gitweb:     http://git.kernel.org/tip/33e03dedd759cc9396252d9641b25d01909a26bb
Author:     Rik van Riel <riel@xxxxxxxxxx>
AuthorDate: Fri, 6 Feb 2015 15:02:02 -0500
Committer:  Borislav Petkov <bp@xxxxxxx>
CommitDate: Thu, 19 Feb 2015 11:15:53 +0100

x86/fpu: Introduce task_disable_lazy_fpu_restore() helper

Currently there are a few magic assignments sprinkled through the
code that disable lazy FPU state restoring, some more effective than
others, and all equally mystifying.

It would be easier to have a helper to explicitly disable lazy
FPU state restoring for a task.

Signed-off-by: Rik van Riel <riel@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Link: http://lkml.kernel.org/r/1423252925-14451-6-git-send-email-riel@xxxxxxxxxx
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
---
 arch/x86/include/asm/fpu-internal.h | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/arch/x86/include/asm/fpu-internal.h b/arch/x86/include/asm/fpu-internal.h
index 217d6d7..9c27f44 100644
--- a/arch/x86/include/asm/fpu-internal.h
+++ b/arch/x86/include/asm/fpu-internal.h
@@ -79,6 +79,16 @@ static inline void __cpu_disable_lazy_restore(unsigned int cpu)
 	per_cpu(fpu_owner_task, cpu) = NULL;
 }
 
+/*
+ * Used to indicate that the FPU state in memory is newer than the FPU
+ * state in registers, and the FPU state should be reloaded next time the
+ * task is run. Only safe on the current task, or non-running tasks.
+ */
+static inline void task_disable_lazy_fpu_restore(struct task_struct *tsk)
+{
+	tsk->thread.fpu.last_cpu = ~0;
+}
+
 static inline int fpu_lazy_restore(struct task_struct *new, unsigned int cpu)
 {
 	return new == this_cpu_read_stable(fpu_owner_task) &&
--
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