[PATCH 18/27] x86/fpu: Prepare copy_fpstate_to_sigframe() for TIF_NEED_FPU_LOAD

[Sebastian Andrzej Siewior]

From: Rik van Riel <riel@xxxxxxxxxxx>

The FPU registers need only to be saved if TIF_NEED_FPU_LOAD is not set.
Otherwise this has been already done and can be skipped.

Signed-off-by: Rik van Riel <riel@xxxxxxxxxxx>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
---
 arch/x86/kernel/fpu/signal.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c
index e565881678a87..c98c7bca13bc0 100644
--- a/arch/x86/kernel/fpu/signal.c
+++ b/arch/x86/kernel/fpu/signal.c
@@ -171,7 +171,17 @@ int copy_fpstate_to_sigframe(void __user *buf, void __user *buf_fx, int size)
 			sizeof(struct user_i387_ia32_struct), NULL,
 			(struct _fpstate_32 __user *) buf) ? -1 : 1;
 
-	copy_fpregs_to_fpstate(fpu);
+	fpregs_lock();
+	/*
+	 * If we do not need to load the FPU registers at return to userspace
+	 * then the CPU has the current state and we need to save it. Otherwise
+	 * it is already done and we can skip it.
+	 */
+	if (!test_thread_flag(TIF_NEED_FPU_LOAD)) {
+		copy_fpregs_to_fpstate(fpu);
+		set_thread_flag(TIF_NEED_FPU_LOAD);
+	}
+	fpregs_unlock();
 
 	if (using_compacted_format()) {
 		if (copy_xstate_to_user(buf_fx, xsave, 0, size))
-- 
2.20.1