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

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Date:	Tue, 10 Mar 2015 07:06:25 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	X86 ML <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH 2/2] x86/fpu: factor out memset(xstate, 0) in fpu_finit() paths

From: Oleg Nesterov <oleg@...hat.com>

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>
Acked-by: Rik van Riel <riel@...hat.com>
Cc: Andy Lutomirski <luto@...capital.net>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Tavis Ormandy <taviso@...gle.com>
Cc: <x86@...nel.org>
Link: http://lkml.kernel.org/r/20150302183257.GC23085@redhat.com
Signed-off-by: Borislav Petkov <bp@...e.de>
---
 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 61609b963eab..5fa1be21ac2a 100644
--- a/arch/x86/include/asm/fpu-internal.h
+++ b/arch/x86/include/asm/fpu-internal.h
@@ -135,7 +135,6 @@ 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 03cc0add8694..0f3de6674ae3 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;
-- 
2.2.0.33.gc18b867

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