[RFC PATCH 6/6] ARM: implement THREAD_INFO_IN_TASK for uniprocessor systems
Ard Biesheuvel
ardb at kernel.org
Fri Nov 26 02:10:06 PST 2021
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.
Signed-off-by: Ard Biesheuvel <ardb at kernel.org>
---
arch/arm/Kconfig | 8 +-
arch/arm/include/asm/assembler.h | 115 ++++++++++++++------
arch/arm/include/asm/current.h | 56 ++++++++--
arch/arm/include/asm/switch_to.h | 3 +-
arch/arm/include/asm/thread_info.h | 27 -----
arch/arm/kernel/asm-offsets.c | 3 -
arch/arm/kernel/entry-armv.S | 11 +-
arch/arm/kernel/head-common.S | 4 +-
arch/arm/kernel/process.c | 7 +-
arch/arm/kernel/traps.c | 4 +
10 files changed, 156 insertions(+), 82 deletions(-)
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 61fc5cc03042..3d7476ca4d94 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -126,8 +126,8 @@ 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.
@@ -1169,7 +1169,7 @@ config CURRENT_POINTER_IN_TPIDRURO
config IRQSTACKS
def_bool y
- depends on GENERIC_IRQ_MULTI_HANDLER && THREAD_INFO_IN_TASK
+ depends on GENERIC_IRQ_MULTI_HANDLER
select HAVE_IRQ_EXIT_ON_IRQ_STACK
select HAVE_SOFTIRQ_ON_OWN_STACK
@@ -1619,7 +1619,7 @@ 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
diff --git a/arch/arm/include/asm/assembler.h b/arch/arm/include/asm/assembler.h
index c4c1d5b2edf5..978fdaaac680 100644
--- a/arch/arm/include/asm/assembler.h
+++ b/arch/arm/include/asm/assembler.h
@@ -203,43 +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
- adr_l \t1, __entry_task @ get __entry_task base address
- mrc p15, 0, \t2, c13, c0, 4 @ get per-CPU offset
- ldr \t1, [\t1, \t2] @ load variable
- 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
/*
@@ -333,6 +302,90 @@ ALT_UP_B(.L1_\@)
#endif
.endm
+ /*
+ * load_current - load the current task pointer from the global
+ * variable '__current'
+ */
+ .macro load_current, rd
+#if defined(CONFIG_THUMB2_KERNEL) || \
+ (defined(MODULE) && defined(CONFIG_ARM_MODULE_PLTS)) || \
+ (defined(CONFIG_LD_IS_LLD) && CONFIG_LLD_VERSION < 140000)
+ mov_l \rd, __current
+ ldr \rd, [\rd]
+#else
+ /*
+ * Avoid a literal load, by emitting a sequence of ADD/LDR instructions
+ * with the appropriate relocations. The combined sequence has a range
+ * of -/+ 256 MiB, which should be sufficient for the core kernel and
+ * for modules loaded into the module region.
+ */
+ .globl __current
+ .reloc .L0_\@, R_ARM_ALU_PC_G0_NC, __current
+ .reloc .L1_\@, R_ARM_ALU_PC_G1_NC, __current
+ .reloc .L2_\@, R_ARM_LDR_PC_G2, __current
+.L0_\@: sub \rd, pc, #8
+.L1_\@: sub \rd, \rd, #4
+.L2_\@: ldr \rd, [\rd, #0]
+#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(.L1_\@)
+.L0_\@:
+ .subsection 1
+.L1_\@: ldr \tmp, =__current
+ str \rn, [\tmp]
+ b .L0_\@
+ .previous
+#endif
+#else
+ str_l \rn, __current, \tmp
+#endif
+ .endm
+
+ /*
+ * get_current - load the task pointer of this CPU's current task
+ */
+ .macro get_current, rd
+#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(.L1_\@)
+.L0_\@:
+ .subsection 1
+.L1_\@: load_current \rd
+ b .L0_\@
+ .previous
+#endif
+#else
+ load_current \rd
+#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
+ adr_l \t1, __entry_task @ get __entry_task base address
+ mrc p15, 0, \t2, c13, c0, 4 @ get per-CPU offset
+ ldr \t1, [\t1, \t2] @ load variable
+ mcr p15, 0, \t1, c13, c0, 3 @ store in TPIDRURO
+.L0_\@:
+#endif
+ .endm
+
/*
* Instruction barrier
*/
diff --git a/arch/arm/include/asm/current.h b/arch/arm/include/asm/current.h
index 6bf0aad672c3..68d6907c9d54 100644
--- a/arch/arm/include/asm/current.h
+++ b/arch/arm/include/asm/current.h
@@ -11,22 +11,50 @@
struct task_struct;
+extern struct task_struct *__current;
+extern unsigned int smp_on_up;
+
static inline void set_current(struct task_struct *cur)
{
- if (!IS_ENABLED(CONFIG_CURRENT_POINTER_IN_TPIDRURO))
+ if (!IS_ENABLED(CONFIG_CURRENT_POINTER_IN_TPIDRURO) &&
+ !(IS_ENABLED(CONFIG_SMP) &&
+ IS_ENABLED(CONFIG_SMP_ON_UP) &&
+ smp_on_up)) {
+ __current = cur;
return;
+ }
/* Set TPIDRURO */
asm("mcr p15, 0, %0, c13, c0, 3" :: "r"(cur) : "memory");
}
-#ifdef CONFIG_CURRENT_POINTER_IN_TPIDRURO
+/*
+ * Avoid a literal load by emitting a sequence of ADD/LDR instructions with the
+ * appropriate relocations. The combined sequence has a range of -/+ 256 MiB,
+ * which should be sufficient for the core kernel as well as modules loaded
+ * into the module region. (Not supported by LLD before release 14)
+ */
+#if !defined(CONFIG_LD_IS_LLD) || CONFIG_LLD_VERSION >= 140000
+#define LOAD_CURRENT \
+ " .globl __current \n\t" \
+ " .reloc 10f, R_ARM_ALU_PC_G0_NC, __current \n\t" \
+ " .reloc 11f, R_ARM_ALU_PC_G1_NC, __current \n\t" \
+ " .reloc 12f, R_ARM_LDR_PC_G2, __current \n\t" \
+ "10: sub %0, pc, #8 \n\t" \
+ "11: sub %0, %0, #4 \n\t" \
+ "12: ldr %0, [%0, #0] \n\t"
+#else
+#define LOAD_CURRENT \
+ " ldr %0, =__current \n\t" \
+ " ldr %0, [%0] \n\t"
+#endif
-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 +67,30 @@ 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_CURRENT
+ " 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 defined(CONFIG_THUMB2_KERNEL) || \
+ (defined(MODULE) && defined(CONFIG_ARM_MODULE_PLTS))
+ cur = __current;
#else
- asm("mrc p15, 0, %0, c13, c0, 3" : "=r"(cur));
+ asm(LOAD_CURRENT : "=r"(cur));
#endif
return cur;
}
#define current get_current()
-#else
-#include <asm-generic/current.h>
-#endif /* CONFIG_CURRENT_POINTER_IN_TPIDRURO */
#endif /* __ASSEMBLY__ */
diff --git a/arch/arm/include/asm/switch_to.h b/arch/arm/include/asm/switch_to.h
index b55c7b2755e4..a482c99934ff 100644
--- a/arch/arm/include/asm/switch_to.h
+++ b/arch/arm/include/asm/switch_to.h
@@ -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)
diff --git a/arch/arm/include/asm/thread_info.h b/arch/arm/include/asm/thread_info.h
index 004b89d86224..aecc403b2880 100644
--- a/arch/arm/include/asm/thread_info.h
+++ b/arch/arm/include/asm/thread_info.h
@@ -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) \
diff --git a/arch/arm/kernel/asm-offsets.c b/arch/arm/kernel/asm-offsets.c
index 645845e4982a..2c8d76fd7c66 100644
--- a/arch/arm/kernel/asm-offsets.c
+++ b/arch/arm/kernel/asm-offsets.c
@@ -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));
diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S
index 09a9fe501094..5f3b882d53b7 100644
--- a/arch/arm/kernel/entry-armv.S
+++ b/arch/arm/kernel/entry-armv.S
@@ -816,12 +816,13 @@ 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
@@ -838,7 +839,7 @@ 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
@@ -860,7 +861,7 @@ 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
diff --git a/arch/arm/kernel/head-common.S b/arch/arm/kernel/head-common.S
index da18e0a17dc2..42cae73fcc19 100644
--- a/arch/arm/kernel/head-common.S
+++ b/arch/arm/kernel/head-common.S
@@ -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
diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c
index d47159f3791c..0617af11377f 100644
--- a/arch/arm/kernel/process.c
+++ b/arch/arm/kernel/process.c
@@ -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",
diff --git a/arch/arm/kernel/traps.c b/arch/arm/kernel/traps.c
index b28a705c49cb..3f38357efc46 100644
--- a/arch/arm/kernel/traps.c
+++ b/arch/arm/kernel/traps.c
@@ -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);
--
2.30.2
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