[tip:x86/fpu] x86/fpu: Decouple fpregs_activate()/fpregs_deactivate() from fpu->fpregs_active - tip-bot for Ingo Molnar

From: tip-bot for Ingo Molnar <tipbot@zytor.com>
To: linux-tip-commits@vger.kernel.org
Cc: torvalds@linux-foundation.org, yu-cheng.yu@intel.com,
	peterz@infradead.org, hpa@zytor.com, oleg@redhat.com,
	linux-kernel@vger.kernel.org, bp@alien8.de, ebiggers3@gmail.com,
	riel@redhat.com, tglx@linutronix.de, mingo@kernel.org,
	luto@kernel.org, dave.hansen@linux.intel.com,
	fenghua.yu@intel.com, akpm@linux-foundation.org,
	luto@amacapital.net
Subject: [tip:x86/fpu] x86/fpu: Decouple fpregs_activate()/fpregs_deactivate() from fpu->fpregs_active
Date: Tue, 26 Sep 2017 01:28:59 -0700	[thread overview]
Message-ID: <tip-6cf4edbe0526db311a28734609da888fdfcb3604@git.kernel.org> (raw)
In-Reply-To: <20170923130016.21448-20-mingo@kernel.org>

Commit-ID:  6cf4edbe0526db311a28734609da888fdfcb3604
Gitweb:     http://git.kernel.org/tip/6cf4edbe0526db311a28734609da888fdfcb3604
Author:     Ingo Molnar <mingo@kernel.org>
AuthorDate: Sat, 23 Sep 2017 15:00:02 +0200
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Sun, 24 Sep 2017 13:04:34 +0200

x86/fpu: Decouple fpregs_activate()/fpregs_deactivate() from fpu->fpregs_active

The fpregs_activate()/fpregs_deactivate() are currently called in such a pattern:

	if (!fpu->fpregs_active)
		fpregs_activate(fpu);

	...

	if (fpu->fpregs_active)
		fpregs_deactivate(fpu);

But note that it's actually safe to call them without checking the flag first.

This further decouples the fpu->fpregs_active flag from actual FPU logic.

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Eric Biggers <ebiggers3@gmail.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Yu-cheng Yu <yu-cheng.yu@intel.com>
Link: http://lkml.kernel.org/r/20170923130016.21448-20-mingo@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/include/asm/fpu/internal.h | 7 +------
 arch/x86/kernel/fpu/core.c          | 3 +--
 2 files changed, 2 insertions(+), 8 deletions(-)

diff --git a/arch/x86/include/asm/fpu/internal.h b/arch/x86/include/asm/fpu/internal.h
index 7fa676f..42a6016 100644
--- a/arch/x86/include/asm/fpu/internal.h
+++ b/arch/x86/include/asm/fpu/internal.h
@@ -526,8 +526,6 @@ static inline int fpregs_state_valid(struct fpu *fpu, unsigned int cpu)
  */
 static inline void fpregs_deactivate(struct fpu *fpu)
 {
-	WARN_ON_FPU(!fpu->fpregs_active);
-
 	fpu->fpregs_active = 0;
 	this_cpu_write(fpu_fpregs_owner_ctx, NULL);
 	trace_x86_fpu_regs_deactivated(fpu);
@@ -535,8 +533,6 @@ static inline void fpregs_deactivate(struct fpu *fpu)
 
 static inline void fpregs_activate(struct fpu *fpu)
 {
-	WARN_ON_FPU(fpu->fpregs_active);
-
 	fpu->fpregs_active = 1;
 	this_cpu_write(fpu_fpregs_owner_ctx, fpu);
 	trace_x86_fpu_regs_activated(fpu);
@@ -604,8 +600,7 @@ static inline void user_fpu_begin(void)
 	struct fpu *fpu = &current->thread.fpu;
 
 	preempt_disable();
-	if (!fpu->fpregs_active)
-		fpregs_activate(fpu);
+	fpregs_activate(fpu);
 	preempt_enable();
 }
 
diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index eab2446..01a47e9 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -426,8 +426,7 @@ void fpu__drop(struct fpu *fpu)
 			asm volatile("1: fwait\n"
 				     "2:\n"
 				     _ASM_EXTABLE(1b, 2b));
-			if (fpu->fpregs_active)
-				fpregs_deactivate(fpu);
+			fpregs_deactivate(fpu);
 		}
 	} else {
 		WARN_ON_FPU(fpu->fpregs_active);
