[PATCH v5 4/5] ARM: smp: Store current pointer in TPIDRURO register if available
Ard Biesheuvel
ardb at kernel.org
Sat Sep 18 01:44:37 PDT 2021
Now that the user space TLS register is assigned on every return to user
space, we can use it to keep the 'current' pointer while running in the
kernel. This removes the need to access it via thread_info, which is
located at the base of the stack, but will be moved out of there in a
subsequent patch.
Use the __builtin_thread_pointer() helper when available - this will
help GCC understand that reloading the value within the same function is
not necessary, even when using the per-task stack protector (which also
generates accesses via the TLS register). For example, the generated
code below loads TPIDRURO only once, and uses it to access both the
stack canary and the preempt_count fields.
<do_one_initcall>:
e92d 41f0 stmdb sp!, {r4, r5, r6, r7, r8, lr}
ee1d 4f70 mrc 15, 0, r4, cr13, cr0, {3}
4606 mov r6, r0
b094 sub sp, #80 ; 0x50
f8d4 34e8 ldr.w r3, [r4, #1256] ; 0x4e8 <- stack canary
9313 str r3, [sp, #76] ; 0x4c
f8d4 8004 ldr.w r8, [r4, #4] <- preempt count
Co-developed-by: Keith Packard <keithpac at amazon.com>
Signed-off-by: Keith Packard <keithpac at amazon.com>
Signed-off-by: Ard Biesheuvel <ardb at kernel.org>
---
arch/arm/Kconfig | 5 ++
arch/arm/Makefile | 4 ++
arch/arm/include/asm/assembler.h | 24 ++++++++++
arch/arm/include/asm/current.h | 50 ++++++++++++++++++++
arch/arm/include/asm/switch_to.h | 2 +
arch/arm/include/asm/thread_info.h | 2 +
arch/arm/kernel/entry-armv.S | 5 ++
arch/arm/kernel/entry-common.S | 1 +
arch/arm/kernel/head-common.S | 5 ++
arch/arm/kernel/process.c | 4 ++
arch/arm/kernel/smp.c | 2 +
arch/arm/mm/proc-macros.S | 3 +-
12 files changed, 105 insertions(+), 2 deletions(-)
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index ff3e64ae959e..cd195e6f4ea6 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -1157,6 +1157,11 @@ config SMP_ON_UP
If you don't know what to do here, say Y.
+
+config CURRENT_POINTER_IN_TPIDRURO
+ def_bool y
+ depends on SMP && CPU_32v6K && !CPU_V6
+
config ARM_CPU_TOPOLOGY
bool "Support cpu topology definition"
depends on SMP && CPU_V7
diff --git a/arch/arm/Makefile b/arch/arm/Makefile
index b46e673a0ebe..1c540157e283 100644
--- a/arch/arm/Makefile
+++ b/arch/arm/Makefile
@@ -113,6 +113,10 @@ ifeq ($(CONFIG_CC_IS_CLANG),y)
CFLAGS_ABI += -meabi gnu
endif
+ifeq ($(CONFIG_CURRENT_POINTER_IN_TPIDRURO),y)
+CFLAGS_ABI += -mtp=cp15
+endif
+
# Accept old syntax despite ".syntax unified"
AFLAGS_NOWARN :=$(call as-option,-Wa$(comma)-mno-warn-deprecated,-Wa$(comma)-W)
diff --git a/arch/arm/include/asm/assembler.h b/arch/arm/include/asm/assembler.h
index e2b1fd558bf3..c1551dee28be 100644
--- a/arch/arm/include/asm/assembler.h
+++ b/arch/arm/include/asm/assembler.h
@@ -199,6 +199,30 @@
.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.
*/
diff --git a/arch/arm/include/asm/current.h b/arch/arm/include/asm/current.h
new file mode 100644
index 000000000000..1d472fa7697b
--- /dev/null
+++ b/arch/arm/include/asm/current.h
@@ -0,0 +1,50 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (c) 2021 Keith Packard <keithp at keithp.com>
+ * Copyright (c) 2021 Google, LLC <ardb at kernel.org>
+ */
+
+#ifndef _ASM_ARM_CURRENT_H
+#define _ASM_ARM_CURRENT_H
+
+#ifndef __ASSEMBLY__
+
+struct task_struct;
+
+static inline void set_current(struct task_struct *cur)
+{
+ if (!IS_ENABLED(CONFIG_CURRENT_POINTER_IN_TPIDRURO))
+ return;
+
+ /* 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)
+{
+ struct task_struct *cur;
+
+#if __has_builtin(__builtin_thread_pointer)
+ /*
+ * Use the __builtin helper when available - this results in better
+ * code, especially when using GCC in combination with the per-task
+ * stack protector, as the compiler will recognize that it needs to
+ * load the TLS register only once in every function.
+ */
+ cur = __builtin_thread_pointer();
+#else
+ asm("mrc p15, 0, %0, c13, c0, 3" : "=r"(cur));
+#endif
+ return cur;
+}
+
+#define current get_current()
+#else
+#include <asm-generic/current.h>
+#endif /* CONFIG_CURRENT_POINTER_IN_TPIDRURO */
+
+#endif /* __ASSEMBLY__ */
+
+#endif /* _ASM_ARM_CURRENT_H */
diff --git a/arch/arm/include/asm/switch_to.h b/arch/arm/include/asm/switch_to.h
index 007d8fea7157..61e4a3c4ca6e 100644
--- a/arch/arm/include/asm/switch_to.h
+++ b/arch/arm/include/asm/switch_to.h
@@ -26,6 +26,8 @@ extern struct task_struct *__switch_to(struct task_struct *, struct thread_info
#define switch_to(prev,next,last) \
do { \
__complete_pending_tlbi(); \
+ if (IS_ENABLED(CONFIG_CURRENT_POINTER_IN_TPIDRURO)) \
+ __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 f0cacc733231..76b6fbd5540c 100644
--- a/arch/arm/include/asm/thread_info.h
+++ b/arch/arm/include/asm/thread_info.h
@@ -29,6 +29,8 @@
struct task_struct;
+DECLARE_PER_CPU(struct task_struct *, __entry_task);
+
#include <asm/types.h>
struct cpu_context_save {
diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S
index 241b73d64df7..7263a45abf3d 100644
--- a/arch/arm/kernel/entry-armv.S
+++ b/arch/arm/kernel/entry-armv.S
@@ -384,6 +384,8 @@ ENDPROC(__fiq_abt)
ATRAP( teq r8, r7)
ATRAP( mcrne p15, 0, r8, c1, c0, 0)
+ reload_current r7, r8
+
@
@ Clear FP to mark the first stack frame
@
@@ -762,6 +764,8 @@ ENTRY(__switch_to)
add r7, r7, #TSK_STACK_CANARY & ~IMM12_MASK
.endif
ldr r7, [r7, #TSK_STACK_CANARY & IMM12_MASK]
+#elif defined(CONFIG_CURRENT_POINTER_IN_TPIDRURO)
+ ldr r7, [r2, #TI_TASK]
#endif
#ifdef CONFIG_CPU_USE_DOMAINS
mcr p15, 0, r6, c3, c0, 0 @ Set domain register
@@ -776,6 +780,7 @@ ENTRY(__switch_to)
#endif
THUMB( mov ip, r4 )
mov r0, r5
+ set_current r7
ARM( ldmia r4, {r4 - sl, fp, sp, pc} ) @ Load all regs saved previously
THUMB( ldmia ip!, {r4 - sl, fp} ) @ Load all regs saved previously
THUMB( ldr sp, [ip], #4 )
diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S
index d9c99db50243..ac86c34682bb 100644
--- a/arch/arm/kernel/entry-common.S
+++ b/arch/arm/kernel/entry-common.S
@@ -170,6 +170,7 @@ ENTRY(vector_swi)
str saved_psr, [sp, #S_PSR] @ Save CPSR
str r0, [sp, #S_OLD_R0] @ Save OLD_R0
#endif
+ reload_current r10, ip
zero_fp
alignment_trap r10, ip, __cr_alignment
asm_trace_hardirqs_on save=0
diff --git a/arch/arm/kernel/head-common.S b/arch/arm/kernel/head-common.S
index 29b2eda136bb..da18e0a17dc2 100644
--- a/arch/arm/kernel/head-common.S
+++ b/arch/arm/kernel/head-common.S
@@ -105,6 +105,11 @@ __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
+
ldmia r4, {r0, r1, r2, r3}
str r9, [r0] @ Save processor ID
str r7, [r1] @ Save machine type
diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c
index cd73c216b272..30428d756515 100644
--- a/arch/arm/kernel/process.c
+++ b/arch/arm/kernel/process.c
@@ -36,6 +36,10 @@
#include "signal.h"
+#ifdef CONFIG_CURRENT_POINTER_IN_TPIDRURO
+DEFINE_PER_CPU(struct task_struct *, __entry_task);
+#endif
+
#if defined(CONFIG_STACKPROTECTOR) && !defined(CONFIG_STACKPROTECTOR_PER_TASK)
#include <linux/stackprotector.h>
unsigned long __stack_chk_guard __read_mostly;
diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
index 8979d548ec17..97ee6b1567e9 100644
--- a/arch/arm/kernel/smp.c
+++ b/arch/arm/kernel/smp.c
@@ -409,6 +409,8 @@ asmlinkage void secondary_start_kernel(struct task_struct *task)
struct mm_struct *mm = &init_mm;
unsigned int cpu;
+ set_current(task);
+
secondary_biglittle_init();
/*
diff --git a/arch/arm/mm/proc-macros.S b/arch/arm/mm/proc-macros.S
index e2c743aa2eb2..d48ba99d739c 100644
--- a/arch/arm/mm/proc-macros.S
+++ b/arch/arm/mm/proc-macros.S
@@ -30,8 +30,7 @@
* act_mm - get current->active_mm
*/
.macro act_mm, rd
- get_thread_info \rd
- ldr \rd, [\rd, #TI_TASK]
+ get_current \rd
.if (TSK_ACTIVE_MM > IMM12_MASK)
add \rd, \rd, #TSK_ACTIVE_MM & ~IMM12_MASK
.endif
--
2.30.2
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