Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932267Ab3JNPaL (ORCPT ); Mon, 14 Oct 2013 11:30:11 -0400 Received: from mail-pa0-f41.google.com ([209.85.220.41]:59066 "EHLO mail-pa0-f41.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932239Ab3JNPaG (ORCPT ); Mon, 14 Oct 2013 11:30:06 -0400 Message-ID: <525C0DF8.8040306@gmail.com> Date: Mon, 14 Oct 2013 23:30:00 +0800 From: Jiang Liu User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130510 Thunderbird/17.0.6 MIME-Version: 1.0 To: Will Deacon 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 References: <1381674029-430-1-git-send-email-liuj97@gmail.com> <1381674029-430-2-git-send-email-liuj97@gmail.com> <20131014151638.GI10491@mudshark.cambridge.arm.com> In-Reply-To: <20131014151638.GI10491@mudshark.cambridge.arm.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3628 Lines: 109 On 10/14/2013 11:16 PM, Will Deacon wrote: > 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... Hi Will, We will add an explicit "volatile" here. But according to GCC docs, it should have the same effect: An asm instruction without any output operands is treated identically to a volatile asm instruction. Thanks! Gerry > >> 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/