Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756638Ab3JNPRO (ORCPT ); Mon, 14 Oct 2013 11:17:14 -0400 Received: from cam-admin0.cambridge.arm.com ([217.140.96.50]:47690 "EHLO cam-admin0.cambridge.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750782Ab3JNPRN (ORCPT ); Mon, 14 Oct 2013 11:17:13 -0400 Date: Mon, 14 Oct 2013 16:16:38 +0100 From: Will Deacon To: Jiang Liu Cc: Catalin Marinas , Jiang Liu , Ard Biesheuvel , Al Viro , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" Subject: Re: [RFT PATCH v2 2/4] arm64: restore FPSIMD to default state for kernel and signal contexts Message-ID: <20131014151638.GI10491@mudshark.cambridge.arm.com> References: <1381674029-430-1-git-send-email-liuj97@gmail.com> <1381674029-430-2-git-send-email-liuj97@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1381674029-430-2-git-send-email-liuj97@gmail.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3256 Lines: 98 On Sun, Oct 13, 2013 at 03:20:18PM +0100, Jiang Liu wrote: > From: Jiang Liu > > Restore FPSIMD control and status registers to default values > when creating new FPSIMD contexts for kernel context and reset > FPSIMD status register when creating FPSIMD context for signal > handling, otherwise the stale value in FPSIMD control and status > registers may affect the new kernal or signal handling contexts. > > Signed-off-by: Jiang Liu > Cc: Jiang Liu > --- > arch/arm64/include/asm/fpsimd.h | 16 ++++++++++++++++ > arch/arm64/kernel/fpsimd.c | 11 +++++++++-- > arch/arm64/kernel/signal.c | 1 + > arch/arm64/kernel/signal32.c | 1 + > 4 files changed, 27 insertions(+), 2 deletions(-) > > diff --git a/arch/arm64/include/asm/fpsimd.h b/arch/arm64/include/asm/fpsimd.h > index c43b4ac..b2dc30f 100644 > --- a/arch/arm64/include/asm/fpsimd.h > +++ b/arch/arm64/include/asm/fpsimd.h > @@ -50,8 +50,24 @@ struct fpsimd_state { > #define VFP_STATE_SIZE ((32 * 8) + 4) > #endif > > +#define AARCH64_FPCR_DEFAULT_VAL 0 > + > struct task_struct; > > +static inline void fpsimd_init_hw_state(void) > +{ > + int val = AARCH64_FPCR_DEFAULT_VAL; > + > + asm ("msr fpcr, %x0\n" > + "msr fpsr, xzr\n" > + : : "r"(val)); > +} > + > +static inline void fpsimd_clear_fpsr(void) > +{ > + asm ("msr fpsr, xzr\n"); > +} You have pretty weak asm constraints here... > extern void fpsimd_save_state(struct fpsimd_state *state); > extern void fpsimd_load_state(struct fpsimd_state *state); > > diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c > index bb785d2..12a25e5 100644 > --- a/arch/arm64/kernel/fpsimd.c > +++ b/arch/arm64/kernel/fpsimd.c > @@ -80,9 +80,14 @@ void fpsimd_thread_switch(struct task_struct *next) > > void fpsimd_flush_thread(void) > { > + struct fpsimd_state *state = ¤t->thread.fpsimd_state; > + > preempt_disable(); > - memset(¤t->thread.fpsimd_state, 0, sizeof(struct fpsimd_state)); > - fpsimd_load_state(¤t->thread.fpsimd_state); > + memset(state, 0, sizeof(struct fpsimd_state)); > +#if (AARCH64_FPCR_DEFAULT_VAL != 0) > + state->fpcr = AARCH64_FPCR_DEFAULT_VAL; > +#endif > + fpsimd_load_state(state); > preempt_enable(); > } > > @@ -99,6 +104,8 @@ void kernel_neon_begin(void) > > if (current->mm) > fpsimd_save_state(¤t->thread.fpsimd_state); > + > + fpsimd_init_hw_state(); > } > EXPORT_SYMBOL(kernel_neon_begin); > > diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c > index 890a591..4ee231e 100644 > --- a/arch/arm64/kernel/signal.c > +++ b/arch/arm64/kernel/signal.c > @@ -52,6 +52,7 @@ static int preserve_fpsimd_context(struct fpsimd_context __user *ctx) > > /* dump the hardware registers to the fpsimd_state structure */ > fpsimd_save_state(fpsimd); > + fpsimd_clear_fpsr(); ... so I reckon GCC could reorder these two calls, resulting in corruption of the saved state register. Will -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/