linux-kernel - [tip:x86/fpu] x86/fpu: Prepare copy_fpstate_to_sigframe() for TIF_NEED_FPU

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Date:   Sat, 13 Apr 2019 13:58:34 -0700
From:   tip-bot for Rik van Riel <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     bigeasy@...utronix.de, hpa@...or.com, dave.hansen@...el.com,
        tglx@...utronix.de, kvm@...r.kernel.org, bp@...e.de,
        rkrcmar@...hat.com, pbonzini@...hat.com, luto@...nel.org,
        mingo@...hat.com, mingo@...nel.org, x86@...nel.org,
        linux-kernel@...r.kernel.org, Jason@...c4.com, riel@...riel.com,
        jannh@...gle.com
Subject: [tip:x86/fpu] x86/fpu: Prepare copy_fpstate_to_sigframe() for
 TIF_NEED_FPU_LOAD

Commit-ID:  a352a3b7b7920212ee4c45a41500c66826318e92
Gitweb:     https://git.kernel.org/tip/a352a3b7b7920212ee4c45a41500c66826318e92
Author:     Rik van Riel <riel@...riel.com>
AuthorDate: Wed, 3 Apr 2019 18:41:47 +0200
Committer:  Borislav Petkov <bp@...e.de>
CommitDate: Thu, 11 Apr 2019 18:20:04 +0200

x86/fpu: Prepare copy_fpstate_to_sigframe() for TIF_NEED_FPU_LOAD

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.

 [ bp: Massage a bit. ]

Signed-off-by: Rik van Riel <riel@...riel.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Signed-off-by: Borislav Petkov <bp@...e.de>
Reviewed-by: Dave Hansen <dave.hansen@...el.com>
Reviewed-by: Thomas Gleixner <tglx@...utronix.de>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Jann Horn <jannh@...gle.com>
Cc: "Jason A. Donenfeld" <Jason@...c4.com>
Cc: kvm ML <kvm@...r.kernel.org>
Cc: Paolo Bonzini <pbonzini@...hat.com>
Cc: Radim Krčmář <rkrcmar@...hat.com>
Cc: Rik van Riel <riel@...riel.com>
Cc: x86-ml <x86@...nel.org>
Link: https://lkml.kernel.org/r/20190403164156.19645-19-bigeasy@linutronix.de
---
 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 8f23f5237218..9b9dfdc96285 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);
+	/*
+	 * 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 has already been done and we can skip it.
+	 */
+	fpregs_lock();
+	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))