Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1763044Ab3ECPYt (ORCPT ); Fri, 3 May 2013 11:24:49 -0400 Received: from service87.mimecast.com ([91.220.42.44]:39340 "EHLO service87.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1762657Ab3ECPYq convert rfc822-to-8bit (ORCPT ); Fri, 3 May 2013 11:24:46 -0400 Message-ID: <5183D6C3.8090402@arm.com> Date: Fri, 03 May 2013 16:24:51 +0100 From: Jonathan Austin User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130308 Thunderbird/17.0.4 MIME-Version: 1.0 To: Russell King - ARM Linux CC: =?UTF-8?B?QW5kcsOpIEhlbnRzY2hlbA==?= , Will Deacon , "linux-arch@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" Subject: Re: [PATCHv2] arm: Preserve TPIDRURW on context switch References: <517168BB.3070903@dawncrow.de> <20130422143616.GP14496@n2100.arm.linux.org.uk> <20130422151836.GA15665@mudshark.cambridge.arm.com> <5175A697.3080308@dawncrow.de> <20130423091536.GB17593@mudshark.cambridge.arm.com> <51770E4E.2040003@dawncrow.de> <20130424094251.GA21850@mudshark.cambridge.arm.com> <5182C480.3080001@dawncrow.de> <5183819E.50308@arm.com> <20130503095547.GD18614@n2100.arm.linux.org.uk> In-Reply-To: <20130503095547.GD18614@n2100.arm.linux.org.uk> X-OriginalArrivalTime: 03 May 2013 15:24:44.0085 (UTC) FILETIME=[56A8FE50:01CE4812] X-MC-Unique: 113050316244416201 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 16329 Lines: 496 Hi Russell, Thanks for the comments - you're right about the 'switch_tls' being more appropriate - needed to take a step back to see that. I've got a few questions, added inline. André, Assuming I've understood things okay, there's a patch that uses Russell's asm stuff (with minor modifications, see the questions) and includes the C-world changes too. Perhaps you could see that it solves your problem? On 03/05/13 10:55, Russell King - ARM Linux wrote: > On Fri, May 03, 2013 at 10:21:34AM +0100, Jonathan Austin wrote: >> .macro set_tls_v6k, tp, tmp1, tmp2 >> - mcr p15, 0, \tp, c13, c0, 3 @ set TLS register >> - mov \tmp1, #0 >> - mcr p15, 0, \tmp1, c13, c0, 2 @ clear user r/w TLS register >> + ldrd \tmp1, \tmp2, [\tp] >> + mcr p15, 0, \tmp1, c13, c0, 3 @ set user r/o TLS register >> + mcr p15, 0, \tmp2, c13, c0, 2 @ set user r/w TLS register > > So we're still back at stalling the pipeline with result delays on older > CPUs? How much older? This particular bit is v6k specific so I wasn't worrying too much but I guess I'm missing something? It's an academic question wrt to this patch now, though, as the version you show below re-orders to reduce the stalls... > >> + .endm >> + >> + .macro save_tlsuser_v6k, tp, tmp1, tmp2 >> + @ TPIDRURW can be updated from userspace, so we have to re-read it >> + mrc p15, 0, \tmp2, c13, c0, 2 @ load user r/w TLS register >> + str \tmp2, [\tp, #4] >> .endm >> >> .macro set_tls_v6, tp, tmp1, tmp2 >> @@ -16,15 +25,26 @@ >> ldr \tmp1, [\tmp1, #0] >> mov \tmp2, #0xffff0fff >> tst \tmp1, #HWCAP_TLS @ hardware TLS available? >> - mcrne p15, 0, \tp, c13, c0, 3 @ yes, set TLS register >> - movne \tmp1, #0 >> - mcrne p15, 0, \tmp1, c13, c0, 2 @ clear user r/w TLS register >> - streq \tp, [\tmp2, #-15] @ set TLS value at 0xffff0ff0 >> + ldrned \tmp1, \tmp2, [\tp] >> + ldreq \tmp1, [\tp] >> + mcrne p15, 0, \tmp1, c13, c0, 3 @ yes, set user r/o TLS register >> + mcrne p15, 0, \tmp2, c13, c0, 2 @ set user r/w TLS register >> + streq \tmp1, [\tmp2, #-15] @ set TLS value at 0xffff0ff0 > > This at least is better. > >> + .endm >> + >> + .macro save_tlsuser_v6, tp, tmp1, tmp2 >> + @ TPIDRURW can be updated from userspace, so we have to re-read it >> + ldr \tmp1, =elf_hwcap >> + ldr \tmp1, [\tmp1, #0] >> + tst \tmp1, #HWCAP_TLS @ hardware TLS available? > > But this isn't - this involves two delays. Indeed. You left this section untouched in your asm below - was that because you didn't look at optimising it, or because you thought there wasn't much better that could be done with it? As far as I can see, we can't start doing any mcr/mrc operations until we know for sure that the hw implements them, so this is something we're stuck with? Is V6 but not V6k just 1136? > >> + mrcne p15, 0, \tmp2, c13, c0, 2 @ read user r/w TLS register >> + strne \tmp2, [\tp, #4] @ save in to thread_info >> .endm >> >> .macro set_tls_software, tp, tmp1, tmp2 >> - mov \tmp1, #0xffff0fff >> - str \tp, [\tmp1, #-15] @ set TLS value at 0xffff0ff0 >> + ldr \tmp1, [\tp] >> + mov \tmp2, #0xffff0fff >> + str \tmp1, [\tmp2, #-15] @ set TLS value at 0xffff0ff0 >> .endm >> #endif >> >> @@ -32,18 +52,31 @@ >> #define tls_emu 1 >> #define has_tls_reg 1 >> #define set_tls set_tls_none >> +#define save_tlsuser save_tlsuser_none >> +#define get_tlsuser get_tlsuser_none >> #elif defined(CONFIG_CPU_V6) >> #define tls_emu 0 >> #define has_tls_reg (elf_hwcap & HWCAP_TLS) >> #define set_tls set_tls_v6 >> +#define save_tlsuser save_tlsuser_v6 >> +#define get_tlsuser get_tlsuser_v6 >> #elif defined(CONFIG_CPU_32v6K) >> #define tls_emu 0 >> #define has_tls_reg 1 >> #define set_tls set_tls_v6k >> +#define save_tlsuser save_tlsuser_v6k >> +#define get_tlsuser get_tlsuser_v6k >> #else >> #define tls_emu 0 >> #define has_tls_reg 0 >> #define set_tls set_tls_software >> +#define save_tlsuser save_tlsuser_none >> +#define get_tlsuser get_tlsuser_none >> #endif > > This separation of setting and saving the TLS value is actually quite > silly. They're called from the same place, so lets just call it > "switch_tls" instead. Agreed. Thanks for the suggestion. > > Here's just the assembly bits doing that - this is totally untested > of course: > > arch/arm/include/asm/tls.h | 28 +++++++++++++++------------- > arch/arm/kernel/entry-armv.S | 4 ++-- > 2 files changed, 17 insertions(+), 15 deletions(-) > > diff --git a/arch/arm/include/asm/tls.h b/arch/arm/include/asm/tls.h > index 73409e6..9c377f1 100644 > --- a/arch/arm/include/asm/tls.h > +++ b/arch/arm/include/asm/tls.h > @@ -2,27 +2,29 @@ > #define __ASMARM_TLS_H > > #ifdef __ASSEMBLY__ +#include required for TI_TP_VALUE > - .macro set_tls_none, tp, tmp1, tmp2 > + .macro switch_tls_none, base, tp, trw, tmp1, tmp2 > .endm > > - .macro set_tls_v6k, tp, tmp1, tmp2 > + .macro switch_tls_v6k, base, tp, trw, tmp1, tmp2 How do you feel about calling tp and trw something different? tpidro and tpidrw, or tp and tpuser? The naming threw me off slightly first time I read this new signature (tp=thread_pointer/tls_pointer/etc). > + mrc p15, 0, \tmp2, c13, c0, 2 @ get the user r/w register > mcr p15, 0, \tp, c13, c0, 3 @ set TLS register > - mov \tmp1, #0 > - mcr p15, 0, \tmp1, c13, c0, 2 @ clear user r/w TLS register > + mcr p15, 0, \trw, c13, c0, 2 @ and the user r/w register > + str \tmp2, [\base, #TI_TP_VALUE + 4]@ save it > .endm > > - .macro set_tls_v6, tp, tmp1, tmp2 > + .macro switch_tls_v6, base, tp, trw, tmp1, tmp2 > ldr \tmp1, =elf_hwcap > ldr \tmp1, [\tmp1, #0] > mov \tmp2, #0xffff0fff > tst \tmp1, #HWCAP_TLS @ hardware TLS available? > - mcrne p15, 0, \tp, c13, c0, 3 @ yes, set TLS register > - movne \tmp1, #0 > - mcrne p15, 0, \tmp1, c13, c0, 2 @ clear user r/w TLS register > streq \tp, [\tmp2, #-15] @ set TLS value at 0xffff0ff0 > + mrcne p15, 0, \tmp2, c13, c0, 2 @ get the user r/w register > + mcrne p15, 0, \tp, c13, c0, 3 @ yes, set TLS register > + mcrne p15, 0, \trw, c13, c0, 2 @ set user r/w register > + strne \tmp2, [\base, #TI_TP_VALUE + 4]@ save it > .endm > > - .macro set_tls_software, tp, tmp1, tmp2 > + .macro switch_tls_software, base, tp, trw, tmp1, tmp2 > mov \tmp1, #0xffff0fff > str \tp, [\tmp1, #-15] @ set TLS value at 0xffff0ff0 > .endm > @@ -31,19 +33,19 @@ > #ifdef CONFIG_TLS_REG_EMUL > #define tls_emu 1 > #define has_tls_reg 1 > -#define set_tls set_tls_none > +#define switch_tls switch_tls_none > #elif defined(CONFIG_CPU_V6) > #define tls_emu 0 > #define has_tls_reg (elf_hwcap & HWCAP_TLS) > -#define set_tls set_tls_v6 > +#define switch_tls switch_tls_v6 > #elif defined(CONFIG_CPU_32v6K) > #define tls_emu 0 > #define has_tls_reg 1 > -#define set_tls set_tls_v6k > +#define switch_tls switch_tls_v6k > #else > #define tls_emu 0 > #define has_tls_reg 0 > -#define set_tls set_tls_software > +#define switch_tls switch_tls_software > #endif > > #endif /* __ASMARM_TLS_H */ > diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S > index 0f82098..81a08b1 100644 > --- a/arch/arm/kernel/entry-armv.S > +++ b/arch/arm/kernel/entry-armv.S > @@ -728,15 +728,15 @@ ENTRY(__switch_to) > UNWIND(.fnstart ) > UNWIND(.cantunwind ) > add ip, r1, #TI_CPU_SAVE > - ldr r3, [r2, #TI_TP_VALUE] > ARM( stmia ip!, {r4 - sl, fp, sp, lr} ) @ Store most regs on stack > THUMB( stmia ip!, {r4 - sl, fp} ) @ Store most regs on stack > THUMB( str sp, [ip], #4 ) > THUMB( str lr, [ip], #4 ) > + ldrd r4, r5, [r2, #TI_TP_VALUE] > #ifdef CONFIG_CPU_USE_DOMAINS > ldr r6, [r2, #TI_CPU_DOMAIN] > #endif > - set_tls r3, r4, r5 > + switch_tls r2, r4, r5, r3, r7 Looking at the implementation above and the way you use 'base', I think that should be switch_tls r1, r4, r5, r3, r7 not switch_tls r2, r4, r5, r3, r7 That way we save tpidrurw in to the old thread pointer not the new one. > #if defined(CONFIG_CC_STACKPROTECTOR) && !defined(CONFIG_SMP) > ldr r7, [r2, #TI_TASK] > ldr r8, =__stack_chk_guard > > Here's a complete patch including Russell's suggested asm. Tested on TC2, build-tested for 1136 I think we could drop the extra .c file too - though it is kinda nice for keeping include/asm/tls.h clean... ----8<------ diff --git a/arch/arm/include/asm/thread_info.h b/arch/arm/include/asm/thread_info.h index cddda1f..d90be6d 100644 --- a/arch/arm/include/asm/thread_info.h +++ b/arch/arm/include/asm/thread_info.h @@ -58,7 +58,7 @@ struct thread_info { struct cpu_context_save cpu_context; /* cpu context */ __u32 syscall; /* syscall number */ __u8 used_cp[16]; /* thread used copro */ - unsigned long tp_value; + unsigned long tp_value[2]; /* TLS registers */ #ifdef CONFIG_CRUNCH struct crunch_state crunchstate; #endif diff --git a/arch/arm/include/asm/tls.h b/arch/arm/include/asm/tls.h index 73409e6..39bce5b 100644 --- a/arch/arm/include/asm/tls.h +++ b/arch/arm/include/asm/tls.h @@ -2,27 +2,30 @@ #define __ASMARM_TLS_H #ifdef __ASSEMBLY__ - .macro set_tls_none, tp, tmp1, tmp2 +#include + .macro switch_tls_none, base, tp, trw, tmp1, tmp2 .endm - .macro set_tls_v6k, tp, tmp1, tmp2 + .macro switch_tls_v6k, base, tp, trw, tmp1, tmp2 + mrc p15, 0, \tmp2, c13, c0, 2 @ get the user r/w register mcr p15, 0, \tp, c13, c0, 3 @ set TLS register - mov \tmp1, #0 - mcr p15, 0, \tmp1, c13, c0, 2 @ clear user r/w TLS register + mcr p15, 0, \trw, c13, c0, 2 @ and the user r/w register + strne \tmp2, [\base, #TI_TP_VALUE + 4] @ save it .endm - .macro set_tls_v6, tp, tmp1, tmp2 + .macro switch_tls_v6, base, tp, trw, tmp1, tmp2 ldr \tmp1, =elf_hwcap ldr \tmp1, [\tmp1, #0] mov \tmp2, #0xffff0fff tst \tmp1, #HWCAP_TLS @ hardware TLS available? - mcrne p15, 0, \tp, c13, c0, 3 @ yes, set TLS register - movne \tmp1, #0 - mcrne p15, 0, \tmp1, c13, c0, 2 @ clear user r/w TLS register streq \tp, [\tmp2, #-15] @ set TLS value at 0xffff0ff0 + mrcne p15, 0, \tmp2, c13, c0, 2 @ get the user r/w register + mcrne p15, 0, \tp, c13, c0, 3 @ yes, set TLS register + mcrne p15, 0, \trw, c13, c0, 2 @ set user r/w register + strne \tmp2, [\base, #TI_TP_VALUE + 4] @ save it .endm - .macro set_tls_software, tp, tmp1, tmp2 + .macro switch_tls_software, base, tp, trw, tmp1, tmp2 mov \tmp1, #0xffff0fff str \tp, [\tmp1, #-15] @ set TLS value at 0xffff0ff0 .endm @@ -31,19 +34,28 @@ #ifdef CONFIG_TLS_REG_EMUL #define tls_emu 1 #define has_tls_reg 1 -#define set_tls set_tls_none +#define switch_tls switch_tls_none +#define get_tlsuser get_tlsuser_none #elif defined(CONFIG_CPU_V6) #define tls_emu 0 #define has_tls_reg (elf_hwcap & HWCAP_TLS) -#define set_tls set_tls_v6 +#define switch_tls switch_tls_v6 +#define get_tlsuser get_tlsuser_v6 #elif defined(CONFIG_CPU_32v6K) #define tls_emu 0 #define has_tls_reg 1 -#define set_tls set_tls_v6k +#define switch_tls switch_tls_v6k +#define get_tlsuser get_tlsuser_v6k #else #define tls_emu 0 #define has_tls_reg 0 -#define set_tls set_tls_software +#define switch_tls switch_tls_software +#define get_tlsuser get_tlsuser_none #endif +#ifndef __ASSEMBLY__ +extern unsigned long get_tlsuser_none(void); +extern unsigned long get_tlsuser_v6(void); +extern unsigned long get_tlsuser_v6k(void); +#endif #endif /* __ASMARM_TLS_H */ diff --git a/arch/arm/kernel/Makefile b/arch/arm/kernel/Makefile index 5f3338e..4e1114c 100644 --- a/arch/arm/kernel/Makefile +++ b/arch/arm/kernel/Makefile @@ -17,7 +17,7 @@ CFLAGS_REMOVE_return_address.o = -pg obj-y := elf.o entry-armv.o entry-common.o irq.o opcodes.o \ process.o ptrace.o return_address.o sched_clock.o \ - setup.o signal.o stacktrace.o sys_arm.o time.o traps.o + setup.o signal.o stacktrace.o sys_arm.o time.o tls.o traps.o obj-$(CONFIG_ATAGS) += atags_parse.o obj-$(CONFIG_ATAGS_PROC) += atags_proc.o diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S index 0f82098..80f09fe 100644 --- a/arch/arm/kernel/entry-armv.S +++ b/arch/arm/kernel/entry-armv.S @@ -728,15 +728,15 @@ ENTRY(__switch_to) UNWIND(.fnstart ) UNWIND(.cantunwind ) add ip, r1, #TI_CPU_SAVE - ldr r3, [r2, #TI_TP_VALUE] ARM( stmia ip!, {r4 - sl, fp, sp, lr} ) @ Store most regs on stack THUMB( stmia ip!, {r4 - sl, fp} ) @ Store most regs on stack THUMB( str sp, [ip], #4 ) THUMB( str lr, [ip], #4 ) + ldrd r4, r5, [r2, #TI_TP_VALUE] #ifdef CONFIG_CPU_USE_DOMAINS ldr r6, [r2, #TI_CPU_DOMAIN] #endif - set_tls r3, r4, r5 + switch_tls r1, r4, r5, r3, r7 #if defined(CONFIG_CC_STACKPROTECTOR) && !defined(CONFIG_SMP) ldr r7, [r2, #TI_TASK] ldr r8, =__stack_chk_guard diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c index 047d3e4..24dbc72 100644 --- a/arch/arm/kernel/process.c +++ b/arch/arm/kernel/process.c @@ -39,6 +39,7 @@ #include #include #include +#include #ifdef CONFIG_CC_STACKPROTECTOR #include @@ -395,7 +396,8 @@ copy_thread(unsigned long clone_flags, unsigned long stack_start, clear_ptrace_hw_breakpoint(p); if (clone_flags & CLONE_SETTLS) - thread->tp_value = childregs->ARM_r3; + thread->tp_value[0] = childregs->ARM_r3; + thread->tp_value[1] = get_tlsuser(); thread_notify(THREAD_NOTIFY_COPY, thread); diff --git a/arch/arm/kernel/ptrace.c b/arch/arm/kernel/ptrace.c index 03deeff..2bc1514 100644 --- a/arch/arm/kernel/ptrace.c +++ b/arch/arm/kernel/ptrace.c @@ -849,7 +849,7 @@ long arch_ptrace(struct task_struct *child, long request, #endif case PTRACE_GET_THREAD_AREA: - ret = put_user(task_thread_info(child)->tp_value, + ret = put_user(task_thread_info(child)->tp_value[0], datap); break; diff --git a/arch/arm/kernel/tls.c b/arch/arm/kernel/tls.c new file mode 100644 index 0000000..1627f5b --- /dev/null +++ b/arch/arm/kernel/tls.c @@ -0,0 +1,50 @@ +/* + * arch/arm/kernel/tls.c + * + * Copyright (C) 2013 ARM Limited + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License version 2 as + * published by the Free Software Foundation. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with this program; if not, write to the Free Software + * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA + */ + +#include +#include + +/* + * Access to the TPIDRURW register, with full certainty that it exists. + */ +unsigned long get_tlsuser_v6k(void) +{ + unsigned long v; + asm("mrc p15, 0, %0, c13, c0, 2\n" : "=r" (v)); + return v; +} + +/* + * Access to the TPIDRURW register if it exists. + */ +unsigned long get_tlsuser_v6(void) +{ + unsigned long v = 0; + if (elf_hwcap & HWCAP_TLS) + asm("mrc p15, 0, %0, c13, c0, 2\n" : "=r" (v)); + return v; +} + +/* + * Dummy access for the case that TLS is emulated in software + */ +unsigned long get_tlsuser_none(void) +{ + return 0; +} diff --git a/arch/arm/kernel/traps.c b/arch/arm/kernel/traps.c index 1c08911..f9d6259 100644 --- a/arch/arm/kernel/traps.c +++ b/arch/arm/kernel/traps.c @@ -588,7 +588,7 @@ asmlinkage int arm_syscall(int no, struct pt_regs *regs) return regs->ARM_r0; case NR(set_tls): - thread->tp_value = regs->ARM_r0; + thread->tp_value[0] = regs->ARM_r0; if (tls_emu) return 0; if (has_tls_reg) { @@ -706,7 +706,7 @@ static int get_tp_trap(struct pt_regs *regs, unsigned int instr) int reg = (instr >> 12) & 15; if (reg == 15) return 1; - regs->uregs[reg] = current_thread_info()->tp_value; + regs->uregs[reg] = current_thread_info()->tp_value[0]; regs->ARM_pc += 4; return 0; } -- 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/