linux-kernel - [PATCH RFC] x86,fpu: merge save_init_fpu & unlazy

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Message-ID: <20150129160017.6758dd40@cuia.bos.redhat.com>
Date:	Thu, 29 Jan 2015 16:00:17 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Andy Lutomirski <luto@...capital.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Fenghua Yu <fenghua.yu@...el.com>,
	the arch/x86 maintainers <x86@...nel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: [PATCH RFC] x86,fpu: merge save_init_fpu & unlazy_fpu

The functions save_init_fpu and unlazy_fpu do essentially the
same thing: save the fpu context to memory, and call __thread_fpu_end,
which most of the callers do not need or want.

Get rid of the function unlazy_fpu and make sure save_init_fpu does
what unlazy_fpu does today, including preemption safe state saving
in potentially unusual conditions.

Callers of init_fpu do want __thread_fpu_end, so move the call to
__thread_fpu_end into init_fpu.

I am not sure whether math_error requires __thread_fpu_end. One would
think that it would require that in order to sanitize the math state,
before do_device_not_available and math_state_restore restore it,
but those do not currently seem to do that. I am not sure how a task
that catches SIGFPE is supposed to recover and continue...

Signed-off-by: Rik van Riel <riel@...hat.com>
---
 arch/x86/include/asm/fpu-internal.h | 18 ++++++++----------
 arch/x86/include/asm/i387.h         |  2 --
 arch/x86/kernel/i387.c              | 18 ++++--------------
 arch/x86/kernel/traps.c             |  1 +
 4 files changed, 13 insertions(+), 26 deletions(-)

diff --git a/arch/x86/include/asm/fpu-internal.h b/arch/x86/include/asm/fpu-internal.h
index 0dbc08282291..c7e440ddd269 100644
--- a/arch/x86/include/asm/fpu-internal.h
+++ b/arch/x86/include/asm/fpu-internal.h
@@ -524,16 +524,14 @@ static inline void __save_fpu(struct task_struct *tsk)
  */
 static inline void save_init_fpu(struct task_struct *tsk)
 {
-	WARN_ON_ONCE(!__thread_has_fpu(tsk));
-
-	if (use_eager_fpu()) {
-		__save_fpu(tsk);
-		return;
-	}
-
 	preempt_disable();
-	__save_init_fpu(tsk);
-	__thread_fpu_end(tsk);
+	if (__thread_has_fpu(tsk)) {
+		if (use_eager_fpu())
+			__save_fpu(tsk);
+		else
+			__save_init_fpu(tsk);
+	} else if (!use_eager_fpu())
+		tsk->thread.fpu_counter = 0;
 	preempt_enable();
 }
 
@@ -600,7 +598,7 @@ static inline void fpu_copy(struct task_struct *dst, struct task_struct *src)
 		struct fpu *dfpu = &dst->thread.fpu;
 		struct fpu *sfpu = &src->thread.fpu;
 
-		unlazy_fpu(src);
+		save_init_fpu(src);
 		memcpy(dfpu->state, sfpu->state, xstate_size);
 	}
 }
diff --git a/arch/x86/include/asm/i387.h b/arch/x86/include/asm/i387.h
index 6eb6fcb83f63..07836671acfb 100644
--- a/arch/x86/include/asm/i387.h
+++ b/arch/x86/include/asm/i387.h
@@ -101,8 +101,6 @@ static inline int user_has_fpu(void)
 	return current->thread.fpu.has_fpu;
 }
 
-extern void unlazy_fpu(struct task_struct *tsk);
-
 #endif /* __ASSEMBLY__ */
 
 #endif /* _ASM_X86_I387_H */
diff --git a/arch/x86/kernel/i387.c b/arch/x86/kernel/i387.c
index 47348653503a..3afc4e73b07f 100644
--- a/arch/x86/kernel/i387.c
+++ b/arch/x86/kernel/i387.c
@@ -116,18 +116,6 @@ void __kernel_fpu_end(void)
 }
 EXPORT_SYMBOL(__kernel_fpu_end);
 
-void unlazy_fpu(struct task_struct *tsk)
-{
-	preempt_disable();
-	if (__thread_has_fpu(tsk)) {
-		__save_init_fpu(tsk);
-		__thread_fpu_end(tsk);
-	} else
-		tsk->thread.fpu_counter = 0;
-	preempt_enable();
-}
-EXPORT_SYMBOL(unlazy_fpu);
-
 unsigned int mxcsr_feature_mask __read_mostly = 0xffffffffu;
 unsigned int xstate_size;
 EXPORT_SYMBOL_GPL(xstate_size);
@@ -245,8 +233,10 @@ int init_fpu(struct task_struct *tsk)
 	int ret;
 
 	if (tsk_used_math(tsk)) {
-		if (cpu_has_fpu && tsk == current)
-			unlazy_fpu(tsk);
+		if (cpu_has_fpu && tsk == current) {
+			save_init_fpu(tsk);
+			__thread_fpu_end(tsk);
+		}
 		tsk->thread.fpu.last_cpu = ~0;
 		return 0;
 	}
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index fb4cb6adf225..201522fd2c96 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -664,6 +664,7 @@ static void math_error(struct pt_regs *regs, int error_code, int trapnr)
 	 * Save the info for the exception handler and clear the error.
 	 */
 	save_init_fpu(task);
+	__thread_fpu_end(task);
 	task->thread.trap_nr = trapnr;
 	task->thread.error_code = error_code;
 	info.si_signo = SIGFPE;

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