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Subject[patch V3 11/23] x86/entry: Move irq flags tracing to prepare_exit_to_usermode()
This is another step towards more C-code and less convoluted ASM.

Similar to the entry path.

1) invoke the tracer and the preparatory lockdep step
2) invoke context tracking which might turn off RCU
3) invoke the final lockdep step

Annotate the code sections in exit_to_user_mode() accordingly so objtool
won't complain about the tracer and lockdep invocation.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
V3: Convert it to noinstr

V2: New patch simplifying the conversion and addressing Alex' review
comment of redundant tracing.
---
arch/x86/entry/common.c | 17 +++++++++++++++++
arch/x86/entry/entry_32.S | 12 ++++--------
arch/x86/entry/entry_64.S | 4 ----
arch/x86/entry/entry_64_compat.S | 14 +++++---------
4 files changed, 26 insertions(+), 21 deletions(-)

--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c
@@ -71,10 +71,27 @@ static __always_inline void enter_from_u
}
#endif

+/**
+ * exit_to_user_mode - Fixup state when exiting to user mode
+ *
+ * Syscall exit enables interrupts, but the kernel state is interrupts
+ * disabled when this is invoked. Also tell RCU about it.
+ *
+ * 1) Trace interrupts on state
+ * 2) Invoke context tracking if enabled to adjust RCU state
+ * 3) Clear CPU buffers if CPU is affected by MDS and the migitation is on.
+ * 4) Tell lockdep that interrupts are enabled
+ */
static __always_inline void exit_to_user_mode(void)
{
+ instr_begin();
+ __trace_hardirqs_on();
+ lockdep_hardirqs_on_prepare(CALLER_ADDR0);
+ instr_end();
+
user_enter_irqoff();
mds_user_clear_cpu_buffers();
+ lockdep_hardirqs_on(CALLER_ADDR0);
}

static void do_audit_syscall_entry(struct pt_regs *regs, u32 arch)
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -811,8 +811,7 @@ SYM_CODE_START(ret_from_fork)
/* When we fork, we trace the syscall return in the child, too. */
movl %esp, %eax
call syscall_return_slowpath
- STACKLEAK_ERASE
- jmp restore_all
+ jmp .Lsyscall_32_done

/* kernel thread */
1: movl %edi, %eax
@@ -855,7 +854,7 @@ SYM_CODE_START_LOCAL(ret_from_exception)
TRACE_IRQS_OFF
movl %esp, %eax
call prepare_exit_to_usermode
- jmp restore_all
+ jmp restore_all_switch_stack
SYM_CODE_END(ret_from_exception)

SYM_ENTRY(__begin_SYSENTER_singlestep_region, SYM_L_GLOBAL, SYM_A_NONE)
@@ -968,8 +967,7 @@ SYM_FUNC_START(entry_SYSENTER_32)

STACKLEAK_ERASE

-/* Opportunistic SYSEXIT */
- TRACE_IRQS_ON /* User mode traces as IRQs on. */
+ /* Opportunistic SYSEXIT */

/*
* Setup entry stack - we keep the pointer in %eax and do the
@@ -1072,11 +1070,9 @@ SYM_FUNC_START(entry_INT80_32)
movl %esp, %eax
call do_int80_syscall_32
.Lsyscall_32_done:
-
STACKLEAK_ERASE

-restore_all:
- TRACE_IRQS_ON
+restore_all_switch_stack:
SWITCH_TO_ENTRY_STACK
CHECK_AND_APPLY_ESPFIX

--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -172,8 +172,6 @@ SYM_INNER_LABEL(entry_SYSCALL_64_after_h
movq %rsp, %rsi
call do_syscall_64 /* returns with IRQs disabled */

- TRACE_IRQS_ON /* return enables interrupts */
-
/*
* Try to use SYSRET instead of IRET if we're returning to
* a completely clean 64-bit userspace context. If we're not,
@@ -340,7 +338,6 @@ SYM_CODE_START(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:
@@ -617,7 +614,6 @@ SYM_CODE_START_LOCAL(common_interrupt)
.Lretint_user:
mov %rsp,%rdi
call prepare_exit_to_usermode
- TRACE_IRQS_ON

SYM_INNER_LABEL(swapgs_restore_regs_and_return_to_usermode, SYM_L_GLOBAL)
#ifdef CONFIG_DEBUG_ENTRY
--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -132,8 +132,8 @@ SYM_FUNC_START(entry_SYSENTER_compat)
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:
@@ -244,8 +244,8 @@ SYM_INNER_LABEL(entry_SYSCALL_compat_aft
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:
@@ -254,7 +254,7 @@ SYM_INNER_LABEL(entry_SYSCALL_compat_aft
* 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) */
@@ -393,9 +393,5 @@ SYM_CODE_START(entry_INT80_compat)

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
SYM_CODE_END(entry_INT80_compat)
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