linux-kernel - [PATCH 2/2] x86/fpu: factor out memset(xstate, 0) in fpu

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Date:	Mon, 2 Mar 2015 19:32:57 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Tavis Ormandy <taviso@...gle.com>, Borislav Petkov <bp@...en8.de>,
	Ingo Molnar <mingo@...nel.org>
Cc:	Rik van Riel <riel@...hat.com>,
	Andy Lutomirski <luto@...capital.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: [PATCH 2/2] x86/fpu: factor out memset(xstate, 0) in fpu_finit()
	paths

fx_finit() has 2 users but only fpu_finit() needs to nullify xstate,
alloc_bootmem_align() in setup_init_fpu_buf() returns zero-filled
memory.

And note that both memset()'s look confusing. Yes, offsetof() is 0
for ->fxsave or ->fsave, but it would be more clean to turn them into
a single memset() which nullifies fpu->state.

Signed-off-by: Oleg Nesterov <oleg@...hat.com>
---
 arch/x86/include/asm/fpu-internal.h |    1 -
 arch/x86/kernel/i387.c              |    3 ++-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/fpu-internal.h b/arch/x86/include/asm/fpu-internal.h
index 02f2e08..8809b5a 100644
--- a/arch/x86/include/asm/fpu-internal.h
+++ b/arch/x86/include/asm/fpu-internal.h
@@ -107,7 +107,6 @@ static __always_inline __pure bool use_fxsr(void)
 
 static inline void fx_finit(struct i387_fxsave_struct *fx)
 {
-	memset(fx, 0, xstate_size);
 	fx->cwd = 0x37f;
 	fx->mxcsr = MXCSR_DEFAULT;
 }
diff --git a/arch/x86/kernel/i387.c b/arch/x86/kernel/i387.c
index 4b12df8..9b7759f 100644
--- a/arch/x86/kernel/i387.c
+++ b/arch/x86/kernel/i387.c
@@ -224,11 +224,12 @@ void fpu_finit(struct fpu *fpu)
 		return;
 	}
 
+	memset(fpu->state, 0, xstate_size);
+
 	if (cpu_has_fxsr) {
 		fx_finit(&fpu->state->fxsave);
 	} else {
 		struct i387_fsave_struct *fp = &fpu->state->fsave;
-		memset(fp, 0, xstate_size);
 		fp->cwd = 0xffff037fu;
 		fp->swd = 0xffff0000u;
 		fp->twd = 0xffffffffu;
-- 
1.5.5.1


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