linux-kernel - [PATCH 043/208] x86/fpu: Add debugging check to fpu

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Date:	Tue,  5 May 2015 18:24:23 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	linux-kernel@...r.kernel.org
Cc:	Andy Lutomirski <luto@...capital.net>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Fenghua Yu <fenghua.yu@...el.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: [PATCH 043/208] x86/fpu: Add debugging check to fpu_copy()

Also add a bit of documentation.

Reviewed-by: Borislav Petkov <bp@...en8.de>
Cc: Andy Lutomirski <luto@...capital.net>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Fenghua Yu <fenghua.yu@...el.com>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Oleg Nesterov <oleg@...hat.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/kernel/fpu/core.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index 3f3c79c75e37..7711539bcda5 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -203,8 +203,18 @@ void fpstate_free(struct fpu *fpu)
 }
 EXPORT_SYMBOL_GPL(fpstate_free);
 
+/*
+ * Copy the current task's FPU state to a new task's FPU context.
+ *
+ * In the 'eager' case we just save to the destination context.
+ *
+ * In the 'lazy' case we save to the source context, mark the FPU lazy
+ * via stts() and copy the source context into the destination context.
+ */
 static void fpu_copy(struct task_struct *dst, struct task_struct *src)
 {
+	WARN_ON(src != current);
+
 	if (use_eager_fpu()) {
 		memset(&dst->thread.fpu.state->xsave, 0, xstate_size);
 		__save_fpu(dst);
-- 
2.1.0

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