linux-kernel - [RFC PATCH 08/10] x86/fpu: prepare copy_fpstate_to_sigframe for TIF_LOAD

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Message-Id: <20180912133353.20595-9-bigeasy@linutronix.de>
Date:   Wed, 12 Sep 2018 15:33:51 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     linux-kernel@...r.kernel.org
Cc:     x86@...nel.org, Andy Lutomirski <luto@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        kvm@...r.kernel.org, "Jason A. Donenfeld" <Jason@...c4.com>,
        Rik van Riel <riel@...riel.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: [RFC PATCH 08/10] x86/fpu: prepare copy_fpstate_to_sigframe for TIF_LOAD_FPU

From: Rik van Riel <riel@...riel.com>

If TIF_LOAD_FPU is set, then the registers are saved (not loaded). In that case
we skip the saving part.

Signed-off-by: Rik van Riel <riel@...riel.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
---
 arch/x86/kernel/fpu/signal.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c
index ff6e7a67522d8..906efd9572ffa 100644
--- a/arch/x86/kernel/fpu/signal.c
+++ b/arch/x86/kernel/fpu/signal.c
@@ -155,13 +155,17 @@ 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;
 
-	/* Update the thread's fxstate to save the fsave header. */
-	if (ia32_fxstate)
-		copy_fxregs_to_kernel(fpu);
-	else {
-		copy_fpregs_to_fpstate(fpu);
-		fpregs_deactivate(fpu);
+	__fpregs_changes_begin();
+	if (!test_thread_flag(TIF_LOAD_FPU)) {
+		/* Update the thread's fxstate to save the fsave header. */
+		if (ia32_fxstate)
+			copy_fxregs_to_kernel(fpu);
+		else {
+			copy_fpregs_to_fpstate(fpu);
+			fpregs_deactivate(fpu);
+		}
 	}
+	__fpregs_changes_end();
 
 	if (using_compacted_format()) {
 		copy_xstate_to_user(buf_fx, xsave, 0, size);
-- 
2.19.0