[patch V2 08/17] x86/entry: Move syscall irq tracing to C code

Thomas Gleixner
2019-10-23T12:32:59Z

Interrupt state tracing can be safely done in C code. The few stack
operations in assembly do not need to be covered.

Remove the now pointless indirection via .Lsyscall_32_done and jump to
swapgs_restore_regs_and_return_to_usermode directly.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
arch/x86/entry/common.c | 10 ++++++++++
arch/x86/entry/entry_32.S | 17 -----------------
arch/x86/entry/entry_64.S | 6 ------
arch/x86/entry/entry_64_compat.S | 30 ++++--------------------------
4 files changed, 14 insertions(+), 49 deletions(-)

--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c
@@ -218,6 +218,9 @@ static void exit_to_usermode_loop(struct
user_enter_irqoff();

mds_user_clear_cpu_buffers();
+
+ /* The return to usermode reenables interrupts. Tell the tracer */
+ trace_hardirqs_on();
}

#define SYSCALL_EXIT_WORK_FLAGS \
@@ -279,6 +282,9 @@ static void syscall_slow_exit_work(struc
{
struct thread_info *ti;

+ /* User to kernel transition disabled interrupts. */
+ trace_hardirqs_off();
+
enter_from_user_mode();
local_irq_enable();
ti = current_thread_info();
@@ -351,6 +357,7 @@ static __always_inline void do_syscall_3
/* Handles int $0x80 */
__visible void do_int80_syscall_32(struct pt_regs *regs)
{
+ trace_hardirqs_off();
enter_from_user_mode();
local_irq_enable();
do_syscall_32_irqs_on(regs);
@@ -367,6 +374,9 @@ static __always_inline void do_syscall_3
unsigned long landing_pad = (unsigned long)current->mm->context.vdso +
vdso_image_32.sym_int80_landing_pad;

+ /* User to kernel transition disabled interrupts. */
+ trace_hardirqs_off();
+
/*
* SYSENTER loses EIP, and even SYSCALL32 needs us to skip forward
* so that 'regs->ip -= 2' lands back on an int $0x80 instruction.
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -924,12 +924,6 @@ ENTRY(entry_SYSENTER_32)
jnz .Lsysenter_fix_flags
.Lsysenter_flags_fixed:

- /*
- * User mode is traced as though IRQs are on, and SYSENTER
- * turned them off.
- */
- TRACE_IRQS_OFF
-
movl %esp, %eax
call do_fast_syscall_32
/* XEN PV guests always use IRET path */
@@ -939,8 +933,6 @@ ENTRY(entry_SYSENTER_32)
STACKLEAK_ERASE

/* Opportunistic SYSEXIT */
- TRACE_IRQS_ON /* User mode traces as IRQs on. */
-
/*
* Setup entry stack - we keep the pointer in %eax and do the
* switch after almost all user-state is restored.
@@ -1039,12 +1031,6 @@ ENTRY(entry_INT80_32)

SAVE_ALL pt_regs_ax=$-ENOSYS switch_stacks=1 /* save rest */

- /*
- * User mode is traced as though IRQs are on, and the interrupt gate
- * turned them off.
- */
- TRACE_IRQS_OFF
-
movl %esp, %eax
call do_int80_syscall_32
.Lsyscall_32_done:
@@ -1052,11 +1038,8 @@ ENTRY(entry_INT80_32)
STACKLEAK_ERASE

restore_all:
- TRACE_IRQS_IRET
SWITCH_TO_ENTRY_STACK
-.Lrestore_all_notrace:
CHECK_AND_APPLY_ESPFIX
-.Lrestore_nocheck:
/* Switch back to user CR3 */
SWITCH_TO_USER_CR3 scratch_reg=%eax

--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -167,15 +167,11 @@ GLOBAL(entry_SYSCALL_64_after_hwframe)

PUSH_AND_CLEAR_REGS rax=$-ENOSYS

- TRACE_IRQS_OFF
-
/* IRQs are off. */
movq %rax, %rdi
movq %rsp, %rsi
call do_syscall_64 /* returns with IRQs disabled */

- TRACE_IRQS_IRETQ /* we're about to change IF */
-
/*
* Try to use SYSRET instead of IRET if we're returning to
* a completely clean 64-bit userspace context. If we're not,
@@ -342,7 +338,6 @@ ENTRY(ret_from_fork)
UNWIND_HINT_REGS
movq %rsp, %rdi
call syscall_return_slowpath /* returns with IRQs disabled */
- TRACE_IRQS_ON /* user mode is traced as IRQS on */
jmp swapgs_restore_regs_and_return_to_usermode

1:
@@ -606,7 +601,6 @@ END(common_spurious)
GLOBAL(retint_user)
mov %rsp,%rdi
call prepare_exit_to_usermode
- TRACE_IRQS_IRETQ

GLOBAL(swapgs_restore_regs_and_return_to_usermode)
#ifdef CONFIG_DEBUG_ENTRY
--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -129,17 +129,11 @@ ENTRY(entry_SYSENTER_compat)
jnz .Lsysenter_fix_flags
.Lsysenter_flags_fixed:

- /*
- * User mode is traced as though IRQs are on, and SYSENTER
- * turned them off.
- */
- TRACE_IRQS_OFF
-
movq %rsp, %rdi
call do_fast_syscall_32
/* XEN PV guests always use IRET path */
- ALTERNATIVE "testl %eax, %eax; jz .Lsyscall_32_done", \
- "jmp .Lsyscall_32_done", X86_FEATURE_XENPV
+ ALTERNATIVE "testl %eax, %eax; jz swapgs_restore_regs_and_return_to_usermode", \
+ "jmp swapgs_restore_regs_and_return_to_usermode", X86_FEATURE_XENPV
jmp sysret32_from_system_call

.Lsysenter_fix_flags:
@@ -247,17 +241,11 @@ GLOBAL(entry_SYSCALL_compat_after_hwfram
pushq $0 /* pt_regs->r15 = 0 */
xorl %r15d, %r15d /* nospec r15 */

- /*
- * User mode is traced as though IRQs are on, and SYSENTER
- * turned them off.
- */
- TRACE_IRQS_OFF
-
movq %rsp, %rdi
call do_fast_syscall_32
/* XEN PV guests always use IRET path */
- ALTERNATIVE "testl %eax, %eax; jz .Lsyscall_32_done", \
- "jmp .Lsyscall_32_done", X86_FEATURE_XENPV
+ ALTERNATIVE "testl %eax, %eax; jz swapgs_restore_regs_and_return_to_usermode", \
+ "jmp swapgs_restore_regs_and_return_to_usermode", X86_FEATURE_XENPV

/* Opportunistic SYSRET */
sysret32_from_system_call:
@@ -266,7 +254,6 @@ GLOBAL(entry_SYSCALL_compat_after_hwfram
* stack. So let's erase the thread stack right now.
*/
STACKLEAK_ERASE
- TRACE_IRQS_ON /* User mode traces as IRQs on. */
movq RBX(%rsp), %rbx /* pt_regs->rbx */
movq RBP(%rsp), %rbp /* pt_regs->rbp */
movq EFLAGS(%rsp), %r11 /* pt_regs->flags (in r11) */
@@ -403,17 +390,8 @@ ENTRY(entry_INT80_compat)
xorl %r15d, %r15d /* nospec r15 */
cld

- /*
- * User mode is traced as though IRQs are on, and the interrupt
- * gate turned them off.
- */
- TRACE_IRQS_OFF
-
movq %rsp, %rdi
call do_int80_syscall_32
-.Lsyscall_32_done:

- /* Go back to user mode. */
- TRACE_IRQS_ON
jmp swapgs_restore_regs_and_return_to_usermode
END(entry_INT80_compat)