Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756732AbbEVKmf (ORCPT ); Fri, 22 May 2015 06:42:35 -0400 Received: from mailapp01.imgtec.com ([195.59.15.196]:64811 "EHLO mailapp01.imgtec.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756229AbbEVKmd (ORCPT ); Fri, 22 May 2015 06:42:33 -0400 From: Paul Burton To: CC: Paul Burton , Leonid Yegoshin , "Maciej W. Rozycki" , , Leonid Yegoshin , James Hogan , David Daney , Markos Chandras , Ralf Baechle , Manuel Lauss Subject: [PATCH v2] MIPS: tidy up FPU context switching Date: Fri, 22 May 2015 11:42:12 +0100 Message-ID: <1432291332-16966-1-git-send-email-paul.burton@imgtec.com> X-Mailer: git-send-email 2.4.1 In-Reply-To: <1432225242-12470-1-git-send-email-paul.burton@imgtec.com> References: <1432225242-12470-1-git-send-email-paul.burton@imgtec.com> MIME-Version: 1.0 Content-Type: text/plain X-Originating-IP: [192.168.159.131] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 6326 Lines: 197 Rather than saving the scalar FP or vector context in the assembly resume function, reuse the existing C code we have in fpu.h to do exactly that. This reduces duplication, results in a much easier to read resume function & should allow the compiler to optimise out more MSA code due to is_msa_enabled()/cpu_has_msa being known-zero at compile time for kernels without MSA support. As a side effect this correctly disables MSA on the first entry to a task, in which case resume will "return" to ret_from_kernel_thread or ret_from_fork in order to call schedule_tail. This would lead to the disable_msa call in switch_to not being executed, as reported by Leonid. Signed-off-by: Paul Burton Reported-by: Leonid Yegoshin --- How about this (lightly tested for the moment) alternative to 10082? Changes in v2: - Introduce lose_fpu_inatomic to skip the preempt_{en,dis}able calls and operate on the provided struct task_struct, which should be prev rather than current. arch/mips/include/asm/fpu.h | 21 ++++++++++++-------- arch/mips/include/asm/switch_to.h | 21 ++++---------------- arch/mips/kernel/r4k_switch.S | 41 +-------------------------------------- 3 files changed, 18 insertions(+), 65 deletions(-) diff --git a/arch/mips/include/asm/fpu.h b/arch/mips/include/asm/fpu.h index 084780b..87e8c78 100644 --- a/arch/mips/include/asm/fpu.h +++ b/arch/mips/include/asm/fpu.h @@ -164,25 +164,30 @@ static inline int own_fpu(int restore) return ret; } -static inline void lose_fpu(int save) +static inline void lose_fpu_inatomic(int save, struct task_struct *tsk) { - preempt_disable(); if (is_msa_enabled()) { if (save) { - save_msa(current); - current->thread.fpu.fcr31 = + save_msa(tsk); + tsk->thread.fpu.fcr31 = read_32bit_cp1_register(CP1_STATUS); } disable_msa(); - clear_thread_flag(TIF_USEDMSA); + clear_tsk_thread_flag(tsk, TIF_USEDMSA); __disable_fpu(); } else if (is_fpu_owner()) { if (save) - _save_fp(current); + _save_fp(tsk); __disable_fpu(); } - KSTK_STATUS(current) &= ~ST0_CU1; - clear_thread_flag(TIF_USEDFPU); + KSTK_STATUS(tsk) &= ~ST0_CU1; + clear_tsk_thread_flag(tsk, TIF_USEDFPU); +} + +static inline void lose_fpu(int save) +{ + preempt_disable(); + lose_fpu_inatomic(save, current); preempt_enable(); } diff --git a/arch/mips/include/asm/switch_to.h b/arch/mips/include/asm/switch_to.h index e92d6c4b..c429d1a 100644 --- a/arch/mips/include/asm/switch_to.h +++ b/arch/mips/include/asm/switch_to.h @@ -16,29 +16,21 @@ #include #include #include -#include +#include struct task_struct; -enum { - FP_SAVE_NONE = 0, - FP_SAVE_VECTOR = -1, - FP_SAVE_SCALAR = 1, -}; - /** * resume - resume execution of a task * @prev: The task previously executed. * @next: The task to begin executing. * @next_ti: task_thread_info(next). - * @fp_save: Which, if any, FP context to save for prev. * * This function is used whilst scheduling to save the context of prev & load * the context of next. Returns prev. */ extern asmlinkage struct task_struct *resume(struct task_struct *prev, - struct task_struct *next, struct thread_info *next_ti, - s32 fp_save); + struct task_struct *next, struct thread_info *next_ti); extern unsigned int ll_bit; extern struct task_struct *ll_task; @@ -86,8 +78,8 @@ do { if (cpu_has_rw_llb) { \ #define switch_to(prev, next, last) \ do { \ u32 __c0_stat; \ - s32 __fpsave = FP_SAVE_NONE; \ __mips_mt_fpaff_switch_to(prev); \ + lose_fpu_inatomic(1, prev); \ if (cpu_has_dsp) \ __save_dsp(prev); \ if (cop2_present && (KSTK_STATUS(prev) & ST0_CU2)) { \ @@ -99,12 +91,7 @@ do { \ write_c0_status(__c0_stat & ~ST0_CU2); \ } \ __clear_software_ll_bit(); \ - if (test_and_clear_tsk_thread_flag(prev, TIF_USEDFPU)) \ - __fpsave = FP_SAVE_SCALAR; \ - if (test_and_clear_tsk_thread_flag(prev, TIF_USEDMSA)) \ - __fpsave = FP_SAVE_VECTOR; \ - (last) = resume(prev, next, task_thread_info(next), __fpsave); \ - disable_msa(); \ + (last) = resume(prev, next, task_thread_info(next)); \ } while (0) #define finish_arch_switch(prev) \ diff --git a/arch/mips/kernel/r4k_switch.S b/arch/mips/kernel/r4k_switch.S index 04cbbde3..92cd051 100644 --- a/arch/mips/kernel/r4k_switch.S +++ b/arch/mips/kernel/r4k_switch.S @@ -34,7 +34,7 @@ #ifndef USE_ALTERNATE_RESUME_IMPL /* * task_struct *resume(task_struct *prev, task_struct *next, - * struct thread_info *next_ti, s32 fp_save) + * struct thread_info *next_ti) */ .align 5 LEAF(resume) @@ -43,45 +43,6 @@ cpu_save_nonscratch a0 LONG_S ra, THREAD_REG31(a0) - /* - * Check whether we need to save any FP context. FP context is saved - * iff the process has used the context with the scalar FPU or the MSA - * ASE in the current time slice, as indicated by _TIF_USEDFPU and - * _TIF_USEDMSA respectively. switch_to will have set fp_save - * accordingly to an FP_SAVE_ enum value. - */ - beqz a3, 2f - - /* - * We do. Clear the saved CU1 bit for prev, such that next time it is - * scheduled it will start in userland with the FPU disabled. If the - * task uses the FPU then it will be enabled again via the do_cpu trap. - * This allows us to lazily restore the FP context. - */ - PTR_L t3, TASK_THREAD_INFO(a0) - LONG_L t0, ST_OFF(t3) - li t1, ~ST0_CU1 - and t0, t0, t1 - LONG_S t0, ST_OFF(t3) - - /* Check whether we're saving scalar or vector context. */ - bgtz a3, 1f - - /* Save 128b MSA vector context + scalar FP control & status. */ - .set push - SET_HARDFLOAT - cfc1 t1, fcr31 - msa_save_all a0 - .set pop /* SET_HARDFLOAT */ - - sw t1, THREAD_FCR31(a0) - b 2f - -1: /* Save 32b/64b scalar FP context. */ - fpu_save_double a0 t0 t1 # c0_status passed in t0 - # clobbers t1 -2: - #if defined(CONFIG_CC_STACKPROTECTOR) && !defined(CONFIG_SMP) PTR_LA t8, __stack_chk_guard LONG_L t9, TASK_STACK_CANARY(a1) -- 2.4.1 -- 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/