sched/x86: Rewrite the switch_to() code
Move the low-level context switch code to an out-of-line asm stub instead of
using complex inline asm. This allows constructing a new stack frame for the
child process to make it seamlessly flow to ret_from_fork without an extra
test and branch in __switch_to(). It also improves code generation for
__schedule() by using the C calling convention instead of clobbering all
registers.
Signed-off-by: Brian Gerst <brgerst@gmail.com>
Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1471106302-10159-5-git-send-email-brgerst@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git a/arch/x86/kernel/asm-offsets.c b/arch/x86/kernel/asm-offsets.c
index 2bd5c6f..db3a0af 100644
--- a/arch/x86/kernel/asm-offsets.c
+++ b/arch/x86/kernel/asm-offsets.c
@@ -29,6 +29,12 @@
void common(void) {
BLANK();
+ OFFSET(TASK_threadsp, task_struct, thread.sp);
+#ifdef CONFIG_CC_STACKPROTECTOR
+ OFFSET(TASK_stack_canary, task_struct, stack_canary);
+#endif
+
+ BLANK();
OFFSET(TI_flags, thread_info, flags);
OFFSET(TI_status, thread_info, status);
diff --git a/arch/x86/kernel/asm-offsets_32.c b/arch/x86/kernel/asm-offsets_32.c
index ecdc1d2..880aa09 100644
--- a/arch/x86/kernel/asm-offsets_32.c
+++ b/arch/x86/kernel/asm-offsets_32.c
@@ -57,6 +57,11 @@
/* Size of SYSENTER_stack */
DEFINE(SIZEOF_SYSENTER_stack, sizeof(((struct tss_struct *)0)->SYSENTER_stack));
+#ifdef CONFIG_CC_STACKPROTECTOR
+ BLANK();
+ OFFSET(stack_canary_offset, stack_canary, canary);
+#endif
+
#if defined(CONFIG_LGUEST) || defined(CONFIG_LGUEST_GUEST) || defined(CONFIG_LGUEST_MODULE)
BLANK();
OFFSET(LGUEST_DATA_irq_enabled, lguest_data, irq_enabled);
diff --git a/arch/x86/kernel/asm-offsets_64.c b/arch/x86/kernel/asm-offsets_64.c
index d875f97..210927e 100644
--- a/arch/x86/kernel/asm-offsets_64.c
+++ b/arch/x86/kernel/asm-offsets_64.c
@@ -56,6 +56,11 @@
OFFSET(TSS_sp0, tss_struct, x86_tss.sp0);
BLANK();
+#ifdef CONFIG_CC_STACKPROTECTOR
+ DEFINE(stack_canary_offset, offsetof(union irq_stack_union, stack_canary));
+ BLANK();
+#endif
+
DEFINE(__NR_syscall_max, sizeof(syscalls_64) - 1);
DEFINE(NR_syscalls, sizeof(syscalls_64));
diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c
index d86be29..4bedbc0 100644
--- a/arch/x86/kernel/process_32.c
+++ b/arch/x86/kernel/process_32.c
@@ -133,17 +133,20 @@
unsigned long arg, struct task_struct *p, unsigned long tls)
{
struct pt_regs *childregs = task_pt_regs(p);
+ struct fork_frame *fork_frame = container_of(childregs, struct fork_frame, regs);
+ struct inactive_task_frame *frame = &fork_frame->frame;
struct task_struct *tsk;
int err;
- p->thread.sp = (unsigned long) childregs;
+ frame->bp = 0;
+ p->thread.sp = (unsigned long) fork_frame;
p->thread.sp0 = (unsigned long) (childregs+1);
memset(p->thread.ptrace_bps, 0, sizeof(p->thread.ptrace_bps));
if (unlikely(p->flags & PF_KTHREAD)) {
/* kernel thread */
memset(childregs, 0, sizeof(struct pt_regs));
- p->thread.ip = (unsigned long) ret_from_kernel_thread;
+ frame->ret_addr = (unsigned long) ret_from_kernel_thread;
task_user_gs(p) = __KERNEL_STACK_CANARY;
childregs->ds = __USER_DS;
childregs->es = __USER_DS;
@@ -161,7 +164,7 @@
if (sp)
childregs->sp = sp;
- p->thread.ip = (unsigned long) ret_from_fork;
+ frame->ret_addr = (unsigned long) ret_from_fork;
task_user_gs(p) = get_user_gs(current_pt_regs());
p->thread.io_bitmap_ptr = NULL;
diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index 63236d8..827eeed 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -141,12 +141,17 @@
{
int err;
struct pt_regs *childregs;
+ struct fork_frame *fork_frame;
+ struct inactive_task_frame *frame;
struct task_struct *me = current;
p->thread.sp0 = (unsigned long)task_stack_page(p) + THREAD_SIZE;
childregs = task_pt_regs(p);
- p->thread.sp = (unsigned long) childregs;
- set_tsk_thread_flag(p, TIF_FORK);
+ fork_frame = container_of(childregs, struct fork_frame, regs);
+ frame = &fork_frame->frame;
+ frame->bp = 0;
+ frame->ret_addr = (unsigned long) ret_from_fork;
+ p->thread.sp = (unsigned long) fork_frame;
p->thread.io_bitmap_ptr = NULL;
savesegment(gs, p->thread.gsindex);
diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index c85d2c6..7e52f83 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -942,7 +942,6 @@
per_cpu(cpu_current_top_of_stack, cpu) =
(unsigned long)task_stack_page(idle) + THREAD_SIZE;
#else
- clear_tsk_thread_flag(idle, TIF_FORK);
initial_gs = per_cpu_offset(cpu);
#endif
}
