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ARM: implement THREAD_INFO_IN_TASK for uniprocessor systems

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On UP systems, only a single task can be 'current' at the same time,
which means we can use a global variable to track it. This means we can
also enable THREAD_INFO_IN_TASK for those systems, as in that case,
thread_info is accessed via current rather than the other way around,
removing the need to store thread_info at the base of the task stack.
This, in turn, permits us to enable IRQ stacks and vmap'ed stacks on UP
systems as well.

To partially mitigate the performance overhead of this arrangement, use
a ADD/ADD/LDR sequence with the appropriate PC-relative group
relocations to load the value of current when needed. This means that
accessing current will still only require a single load as before,
avoiding the need for a literal to carry the address of the global
variable in each function. However, accessing thread_info will now
require this load as well.

Acked-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Nicolas Pitre <nico@fluxnic.net>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Tested-by: Marc Zyngier <maz@kernel.org>
Tested-by: Vladimir Murzin <vladimir.murzin@arm.com> # ARMv7M
This commit is contained in:
Ard Biesheuvel 2021-11-24 14:08:11 +01:00
parent c275591037
commit 9c46929e79
12 changed files with 116 additions and 92 deletions
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8
arch/arm/Kconfig
View file

@ -127,8 +127,8 @@ config ARM
select PERF_USE_VMALLOC
select RTC_LIB
select SYS_SUPPORTS_APM_EMULATION
select THREAD_INFO_IN_TASK if CURRENT_POINTER_IN_TPIDRURO
select HAVE_ARCH_VMAP_STACK if MMU && THREAD_INFO_IN_TASK && (!LD_IS_LLD || LLD_VERSION >= 140000)
select THREAD_INFO_IN_TASK
select HAVE_ARCH_VMAP_STACK if MMU && (!LD_IS_LLD || LLD_VERSION >= 140000)
select TRACE_IRQFLAGS_SUPPORT if !CPU_V7M
# Above selects are sorted alphabetically; please add new ones
# according to that. Thanks.
@ -1158,7 +1158,7 @@ config CURRENT_POINTER_IN_TPIDRURO
config IRQSTACKS
def_bool y
depends on THREAD_INFO_IN_TASK
depends on MMU
select HAVE_IRQ_EXIT_ON_IRQ_STACK
select HAVE_SOFTIRQ_ON_OWN_STACK
@ -1608,7 +1608,7 @@ config CC_HAVE_STACKPROTECTOR_TLS
config STACKPROTECTOR_PER_TASK
bool "Use a unique stack canary value for each task"
depends on STACKPROTECTOR && THREAD_INFO_IN_TASK && !XIP_DEFLATED_DATA
depends on STACKPROTECTOR && CURRENT_POINTER_IN_TPIDRURO && !XIP_DEFLATED_DATA
depends on GCC_PLUGINS || CC_HAVE_STACKPROTECTOR_TLS
select GCC_PLUGIN_ARM_SSP_PER_TASK if !CC_HAVE_STACKPROTECTOR_TLS
default y

83
arch/arm/include/asm/assembler.h
View file

@ -203,41 +203,12 @@ THUMB( fpreg .req r7 )
.endm
.endr
.macro get_current, rd
#ifdef CONFIG_CURRENT_POINTER_IN_TPIDRURO
mrc p15, 0, \rd, c13, c0, 3 @ get TPIDRURO register
#else
get_thread_info \rd
ldr \rd, [\rd, #TI_TASK]
#endif
.endm
.macro set_current, rn
#ifdef CONFIG_CURRENT_POINTER_IN_TPIDRURO
mcr p15, 0, \rn, c13, c0, 3 @ set TPIDRURO register
#endif
.endm
.macro reload_current, t1:req, t2:req
#ifdef CONFIG_CURRENT_POINTER_IN_TPIDRURO
ldr_this_cpu \t1, __entry_task, \t1, \t2
mcr p15, 0, \t1, c13, c0, 3 @ store in TPIDRURO
#endif
.endm
/*
* Get current thread_info.
*/
.macro get_thread_info, rd
#ifdef CONFIG_THREAD_INFO_IN_TASK
/* thread_info is the first member of struct task_struct */
get_current \rd
#else
ARM( mov \rd, sp, lsr #THREAD_SIZE_ORDER + PAGE_SHIFT )
THUMB( mov \rd, sp )
THUMB( lsr \rd, \rd, #THREAD_SIZE_ORDER + PAGE_SHIFT )
mov \rd, \rd, lsl #THREAD_SIZE_ORDER + PAGE_SHIFT
#endif
.endm
/*
@ -330,6 +301,60 @@ ALT_UP_B(.L1_\@)
#endif
.endm
/*
* set_current - store the task pointer of this CPU's current task
*/
.macro set_current, rn:req, tmp:req
#if defined(CONFIG_CURRENT_POINTER_IN_TPIDRURO) || defined(CONFIG_SMP)
9998: mcr p15, 0, \rn, c13, c0, 3 @ set TPIDRURO register
#ifdef CONFIG_CPU_V6
ALT_UP_B(.L0_\@)
.subsection 1
.L0_\@: str_va \rn, __current, \tmp
b .L1_\@
.previous
.L1_\@:
#endif
#else
str_va \rn, __current, \tmp
#endif
.endm
/*
* get_current - load the task pointer of this CPU's current task
*/
.macro get_current, rd:req
#if defined(CONFIG_CURRENT_POINTER_IN_TPIDRURO) || defined(CONFIG_SMP)
9998: mrc p15, 0, \rd, c13, c0, 3 @ get TPIDRURO register
#ifdef CONFIG_CPU_V6
ALT_UP_B(.L0_\@)
.subsection 1
.L0_\@: ldr_va \rd, __current
b .L1_\@
.previous
.L1_\@:
#endif
#else
ldr_va \rd, __current
#endif
.endm
/*
* reload_current - reload the task pointer of this CPU's current task
* into the TLS register
*/
.macro reload_current, t1:req, t2:req
#if defined(CONFIG_CURRENT_POINTER_IN_TPIDRURO) || defined(CONFIG_SMP)
#ifdef CONFIG_CPU_V6
ALT_SMP(nop)
ALT_UP_B(.L0_\@)
#endif
ldr_this_cpu \t1, __entry_task, \t1, \t2
mcr p15, 0, \t1, c13, c0, 3 @ store in TPIDRURO
.L0_\@:
#endif
.endm
/*
* Instruction barrier
*/

37
arch/arm/include/asm/current.h
View file

@ -8,25 +8,18 @@
#define _ASM_ARM_CURRENT_H
#ifndef __ASSEMBLY__
#include <asm/insn.h>
struct task_struct;
static inline void set_current(struct task_struct *cur)
{
if (!IS_ENABLED(CONFIG_CURRENT_POINTER_IN_TPIDRURO))
return;
extern struct task_struct *__current;
/* Set TPIDRURO */
asm("mcr p15, 0, %0, c13, c0, 3" :: "r"(cur) : "memory");
}
#ifdef CONFIG_CURRENT_POINTER_IN_TPIDRURO
static inline struct task_struct *get_current(void)
static inline __attribute_const__ struct task_struct *get_current(void)
{
struct task_struct *cur;
#if __has_builtin(__builtin_thread_pointer) && \
defined(CONFIG_CURRENT_POINTER_IN_TPIDRURO) && \
!(defined(CONFIG_THUMB2_KERNEL) && \
defined(CONFIG_CC_IS_CLANG) && CONFIG_CLANG_VERSION < 130001)
/*
@ -39,16 +32,30 @@ static inline struct task_struct *get_current(void)
* https://github.com/ClangBuiltLinux/linux/issues/1485
*/
cur = __builtin_thread_pointer();
#elif defined(CONFIG_CURRENT_POINTER_IN_TPIDRURO) || defined(CONFIG_SMP)
asm("0: mrc p15, 0, %0, c13, c0, 3 \n\t"
#ifdef CONFIG_CPU_V6
"1: \n\t"
" .subsection 1 \n\t"
"2: " LOAD_SYM_ARMV6(%0, __current) " \n\t"
" b 1b \n\t"
" .previous \n\t"
" .pushsection \".alt.smp.init\", \"a\" \n\t"
" .long 0b - . \n\t"
" b . + (2b - 0b) \n\t"
" .popsection \n\t"
#endif
: "=r"(cur));
#elif __LINUX_ARM_ARCH__>=7 || \
(defined(MODULE) && defined(CONFIG_ARM_MODULE_PLTS))
cur = __current;
#else
asm("mrc p15, 0, %0, c13, c0, 3" : "=r"(cur));
asm(LOAD_SYM_ARMV6(%0, __current) : "=r"(cur));
#endif
return cur;
}
#define current get_current()
#else
#include <asm-generic/current.h>
#endif /* CONFIG_CURRENT_POINTER_IN_TPIDRURO */
#endif /* __ASSEMBLY__ */

3
arch/arm/include/asm/switch_to.h
View file

@ -40,7 +40,8 @@ static inline void set_ti_cpu(struct task_struct *p)
do { \
__complete_pending_tlbi(); \
set_ti_cpu(next); \
if (IS_ENABLED(CONFIG_CURRENT_POINTER_IN_TPIDRURO)) \
if (IS_ENABLED(CONFIG_CURRENT_POINTER_IN_TPIDRURO) || \
IS_ENABLED(CONFIG_SMP)) \
__this_cpu_write(__entry_task, next); \
last = __switch_to(prev,task_thread_info(prev), task_thread_info(next)); \
} while (0)

27
arch/arm/include/asm/thread_info.h
View file

@ -62,9 +62,6 @@ struct cpu_context_save {
struct thread_info {
unsigned long flags; /* low level flags */
int preempt_count; /* 0 => preemptable, <0 => bug */
#ifndef CONFIG_THREAD_INFO_IN_TASK
struct task_struct *task; /* main task structure */
#endif
__u32 cpu; /* cpu */
__u32 cpu_domain; /* cpu domain */
struct cpu_context_save cpu_context; /* cpu context */
@ -80,39 +77,15 @@ struct thread_info {
#define INIT_THREAD_INFO(tsk) \
{ \
INIT_THREAD_INFO_TASK(tsk) \
.flags = 0, \
.preempt_count = INIT_PREEMPT_COUNT, \
}
#ifdef CONFIG_THREAD_INFO_IN_TASK
#define INIT_THREAD_INFO_TASK(tsk)
static inline struct task_struct *thread_task(struct thread_info* ti)
{
return (struct task_struct *)ti;
}
#else
#define INIT_THREAD_INFO_TASK(tsk) .task = &(tsk),
static inline struct task_struct *thread_task(struct thread_info* ti)
{
return ti->task;
}
/*
* how to get the thread information struct from C
*/
static inline struct thread_info *current_thread_info(void) __attribute_const__;
static inline struct thread_info *current_thread_info(void)
{
return (struct thread_info *)
(current_stack_pointer & ~(THREAD_SIZE - 1));
}
#endif
#define thread_saved_pc(tsk) \
((unsigned long)(task_thread_info(tsk)->cpu_context.pc))
#define thread_saved_sp(tsk) \

3
arch/arm/kernel/asm-offsets.c
View file

@ -43,9 +43,6 @@ int main(void)
BLANK();
DEFINE(TI_FLAGS, offsetof(struct thread_info, flags));
DEFINE(TI_PREEMPT, offsetof(struct thread_info, preempt_count));
#ifndef CONFIG_THREAD_INFO_IN_TASK
DEFINE(TI_TASK, offsetof(struct thread_info, task));
#endif
DEFINE(TI_CPU, offsetof(struct thread_info, cpu));
DEFINE(TI_CPU_DOMAIN, offsetof(struct thread_info, cpu_domain));
DEFINE(TI_CPU_SAVE, offsetof(struct thread_info, cpu_context));

11
arch/arm/kernel/entry-armv.S
View file

@ -807,12 +807,13 @@ ENTRY(__switch_to)
switch_tls r1, r4, r5, r3, r7
#if defined(CONFIG_STACKPROTECTOR) && !defined(CONFIG_SMP) && \
!defined(CONFIG_STACKPROTECTOR_PER_TASK)
ldr r9, [r2, #TI_TASK]
ldr r8, =__stack_chk_guard
.if (TSK_STACK_CANARY > IMM12_MASK)
add r9, r9, #TSK_STACK_CANARY & ~IMM12_MASK
.endif
add r9, r2, #TSK_STACK_CANARY & ~IMM12_MASK
ldr r9, [r9, #TSK_STACK_CANARY & IMM12_MASK]
.else
ldr r9, [r2, #TSK_STACK_CANARY & IMM12_MASK]
.endif
#endif
mov r7, r2 @ Preserve 'next'
#ifdef CONFIG_CPU_USE_DOMAINS
@ -829,7 +830,7 @@ ENTRY(__switch_to)
#endif
mov r0, r5
#if !defined(CONFIG_THUMB2_KERNEL) && !defined(CONFIG_VMAP_STACK)
set_current r7
set_current r7, r8
ldmia r4, {r4 - sl, fp, sp, pc} @ Load all regs saved previously
#else
mov r1, r7
@ -851,7 +852,7 @@ ENTRY(__switch_to)
@ switches us to another stack, with few other side effects. In order
@ to prevent this distinction from causing any inconsistencies, let's
@ keep the 'set_current' call as close as we can to the update of SP.
set_current r1
set_current r1, r2
mov sp, ip
ret lr
#endif

10
arch/arm/kernel/entry-v7m.S
View file

@ -97,15 +97,17 @@ ENTRY(__switch_to)
str sp, [ip], #4
str lr, [ip], #4
mov r5, r0
mov r6, r2 @ Preserve 'next'
add r4, r2, #TI_CPU_SAVE
ldr r0, =thread_notify_head
mov r1, #THREAD_NOTIFY_SWITCH
bl atomic_notifier_call_chain
mov ip, r4
mov r0, r5
ldmia ip!, {r4 - r11} @ Load all regs saved previously
ldr sp, [ip]
ldr pc, [ip, #4]!
mov r1, r6
ldmia r4, {r4 - r12, lr} @ Load all regs saved previously
set_current r1, r2
mov sp, ip
bx lr
.fnend
ENDPROC(__switch_to)

4
arch/arm/kernel/head-common.S
View file

@ -105,10 +105,8 @@ __mmap_switched:
mov r1, #0
bl __memset @ clear .bss
#ifdef CONFIG_CURRENT_POINTER_IN_TPIDRURO
adr_l r0, init_task @ get swapper task_struct
set_current r0
#endif
set_current r0, r1
ldmia r4, {r0, r1, r2, r3}
str r9, [r0] @ Save processor ID

7
arch/arm/kernel/process.c
View file

@ -36,7 +36,7 @@
#include "signal.h"
#ifdef CONFIG_CURRENT_POINTER_IN_TPIDRURO
#if defined(CONFIG_CURRENT_POINTER_IN_TPIDRURO) || defined(CONFIG_SMP)
DEFINE_PER_CPU(struct task_struct *, __entry_task);
#endif
@ -46,6 +46,11 @@ unsigned long __stack_chk_guard __read_mostly;
EXPORT_SYMBOL(__stack_chk_guard);
#endif
#ifndef CONFIG_CURRENT_POINTER_IN_TPIDRURO
asmlinkage struct task_struct *__current;
EXPORT_SYMBOL(__current);
#endif
static const char *processor_modes[] __maybe_unused = {
"USER_26", "FIQ_26" , "IRQ_26" , "SVC_26" , "UK4_26" , "UK5_26" , "UK6_26" , "UK7_26" ,
"UK8_26" , "UK9_26" , "UK10_26", "UK11_26", "UK12_26", "UK13_26", "UK14_26", "UK15_26",

11
arch/arm/kernel/smp.c
View file

@ -403,6 +403,17 @@ static void smp_store_cpu_info(unsigned int cpuid)
check_cpu_icache_size(cpuid);
}
static void set_current(struct task_struct *cur)
{
if (!IS_ENABLED(CONFIG_CURRENT_POINTER_IN_TPIDRURO) && !is_smp()) {
__current = cur;
return;
}
/* Set TPIDRURO */
asm("mcr p15, 0, %0, c13, c0, 3" :: "r"(cur) : "memory");
}
/*
* This is the secondary CPU boot entry. We're using this CPUs
* idle thread stack, but a set of temporary page tables.

4
arch/arm/kernel/traps.c
View file

@ -865,7 +865,9 @@ early_initcall(allocate_overflow_stacks);
asmlinkage void handle_bad_stack(struct pt_regs *regs)
{
unsigned long tsk_stk = (unsigned long)current->stack;
#ifdef CONFIG_IRQSTACKS
unsigned long irq_stk = (unsigned long)this_cpu_read(irq_stack_ptr);
#endif
unsigned long ovf_stk = (unsigned long)this_cpu_read(overflow_stack_ptr);
console_verbose();
@ -873,8 +875,10 @@ asmlinkage void handle_bad_stack(struct pt_regs *regs)
pr_emerg("Task stack: [0x%08lx..0x%08lx]\n",
tsk_stk, tsk_stk + THREAD_SIZE);
#ifdef CONFIG_IRQSTACKS
pr_emerg("IRQ stack: [0x%08lx..0x%08lx]\n",
irq_stk - THREAD_SIZE, irq_stk);
#endif
pr_emerg("Overflow stack: [0x%08lx..0x%08lx]\n",
ovf_stk - OVERFLOW_STACK_SIZE, ovf_stk);