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SubjectRe: [patch V4 part 2 05/18] x86/entry: Move irq tracing on syscall entry to C-code
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On 5/5/20 3:41 PM, Thomas Gleixner wrote:
> Now that the C entry points are safe, move the irq flags tracing code into
> the entry helper:
>
> - Invoke lockdep before calling into context tracking
>
> - Use the safe trace_hardirqs_on_prepare() trace function after context
> tracking established state and RCU is watching.
>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> ---
> arch/x86/entry/common.c | 21 +++++++++++++++++++--
> arch/x86/entry/entry_32.S | 12 ------------
> arch/x86/entry/entry_64.S | 2 --
> arch/x86/entry/entry_64_compat.S | 18 ------------------
> 4 files changed, 19 insertions(+), 34 deletions(-)
>
> --- a/arch/x86/entry/common.c
> +++ b/arch/x86/entry/common.c
> @@ -40,19 +40,36 @@
> #include <trace/events/syscalls.h>
>
> #ifdef CONFIG_CONTEXT_TRACKING
> -/* Called on entry from user mode with IRQs off. */
> +/**
> + * enter_from_user_mode - Establish state when coming from user mode
> + *
> + * Syscall entry disables interrupts, but user mode is traced as interrupts
> + * enabled. Also with NO_HZ_FULL RCU might be idle.
> + *
> + * 1) Tell lockdep that interrupts are disabled
> + * 2) Invoke context tracking if enabled to reactivate RCU
> + * 3) Trace interrupts off state
> + */
> __visible noinstr void enter_from_user_mode(void)
> {
> enum ctx_state state = ct_state();
>
> + lockdep_hardirqs_off(CALLER_ADDR0);
> user_exit_irqoff();
>
> instr_begin();
> CT_WARN_ON(state != CONTEXT_USER);
> + trace_hardirqs_off_prepare();
> instr_end();
> }
> #else
> -static inline void enter_from_user_mode(void) {}
> +static __always_inline void enter_from_user_mode(void)
> +{
> + lockdep_hardirqs_off(CALLER_ADDR0);
> + instr_begin();
> + trace_hardirqs_off_prepare();
> + instr_end();
> +}
> #endif
>
> static noinstr void exit_to_user_mode(void)
> --- a/arch/x86/entry/entry_32.S
> +++ b/arch/x86/entry/entry_32.S
> @@ -967,12 +967,6 @@ SYM_FUNC_START(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 */
> @@ -1082,12 +1076,6 @@ SYM_FUNC_START(entry_INT80_32)
>
> SAVE_ALL pt_regs_ax=$-ENOSYS switch_stacks=1 /* save rest */
>
> - /*
> - * User mode is traced as though IRQs are on, and the interrupt gate
> - * turned them off.
> - */
> - TRACE_IRQS_OFF
> -
> movl %esp, %eax
> call do_int80_syscall_32
> .Lsyscall_32_done:
> --- a/arch/x86/entry/entry_64.S
> +++ b/arch/x86/entry/entry_64.S
> @@ -167,8 +167,6 @@ SYM_INNER_LABEL(entry_SYSCALL_64_after_h
>
> PUSH_AND_CLEAR_REGS rax=$-ENOSYS
>
> - TRACE_IRQS_OFF
> -
> /* IRQs are off. */
> movq %rax, %rdi
> movq %rsp, %rsi
> --- a/arch/x86/entry/entry_64_compat.S
> +++ b/arch/x86/entry/entry_64_compat.S
> @@ -129,12 +129,6 @@ SYM_FUNC_START(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 */
> @@ -247,12 +241,6 @@ SYM_INNER_LABEL(entry_SYSCALL_compat_aft
> 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 */
> @@ -403,12 +391,6 @@ SYM_CODE_START(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:
>

enter_from_user_mode() is also called with the CALL_enter_from_user_mode macro,
which is used in interrupt_entry() and identry. Don't you need to also remove
the TRACE_IRQS_OFF there now?

alex.

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