linux-kernel - [tip:x86/fpu] x86/fpu: Split the state handling in fpu_

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Message-ID: <tip-b6aa85558d7e7b18fc3470d2bc1731d2205dd275@git.kernel.org>
Date:   Tue, 26 Sep 2017 01:28:10 -0700
From:   tip-bot for Ingo Molnar <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     mingo@...nel.org, dave.hansen@...ux.intel.com, riel@...hat.com,
        yu-cheng.yu@...el.com, akpm@...ux-foundation.org,
        peterz@...radead.org, luto@...nel.org,
        torvalds@...ux-foundation.org, fenghua.yu@...el.com,
        ebiggers3@...il.com, luto@...capital.net, oleg@...hat.com,
        tglx@...utronix.de, hpa@...or.com, bp@...en8.de,
        linux-kernel@...r.kernel.org
Subject: [tip:x86/fpu] x86/fpu: Split the state handling in fpu__drop()

Commit-ID:  b6aa85558d7e7b18fc3470d2bc1731d2205dd275
Gitweb:     http://git.kernel.org/tip/b6aa85558d7e7b18fc3470d2bc1731d2205dd275
Author:     Ingo Molnar <mingo@...nel.org>
AuthorDate: Sat, 23 Sep 2017 15:00:00 +0200
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Sun, 24 Sep 2017 13:04:34 +0200

x86/fpu: Split the state handling in fpu__drop()

Prepare fpu__drop() to use fpu->fpregs_active.

There are two distinct usecases for fpu__drop() in this context:
exit_thread() when called for 'current' in exit(), and when called
for another task in fork().

This patch does not change behavior, it only adds a couple of
debug checks and structures the code to make the ->fpregs_active
change more obviously correct.

All the complications will be removed later on.

Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Andy Lutomirski <luto@...capital.net>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Eric Biggers <ebiggers3@...il.com>
Cc: Fenghua Yu <fenghua.yu@...el.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Oleg Nesterov <oleg@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Rik van Riel <riel@...hat.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Yu-cheng Yu <yu-cheng.yu@...el.com>
Link: http://lkml.kernel.org/r/20170923130016.21448-18-mingo@kernel.org
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/kernel/fpu/core.c | 19 +++++++++++++------
 1 file changed, 13 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index b7dc383..815dfba 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -414,12 +414,19 @@ void fpu__drop(struct fpu *fpu)
 {
 	preempt_disable();
 
-	if (fpu->fpregs_active) {
-		/* Ignore delayed exceptions from user space */
-		asm volatile("1: fwait\n"
-			     "2:\n"
-			     _ASM_EXTABLE(1b, 2b));
-		fpregs_deactivate(fpu);
+	if (fpu == &current->thread.fpu) {
+		WARN_ON_FPU(fpu->fpstate_active != fpu->fpregs_active);
+
+		if (fpu->fpregs_active) {
+			/* Ignore delayed exceptions from user space */
+			asm volatile("1: fwait\n"
+				     "2:\n"
+				     _ASM_EXTABLE(1b, 2b));
+			if (fpu->fpregs_active)
+				fpregs_deactivate(fpu);
+		}
+	} else {
+		WARN_ON_FPU(fpu->fpregs_active);
 	}
 
 	fpu->fpstate_active = 0;