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SubjectRe: [PATCH v2 6/7] x86/entry/64: Remove TRACE_IRQS_*_DEBUG
On Thu, 04 Jul 2019 21:56:01 +0200
Peter Zijlstra <peterz@infradead.org> wrote:

> Since INT3/#BP no longer runs on an IST, this workaround is no longer
> required.
>
> Tested by running lockdep+ftrace as described in the initial commit:
>
> 5963e317b1e9 ("ftrace/x86: Do not change stacks in DEBUG when calling lockdep")

It looks like a clean revert, and it passed my ftrace smoke tests with
lockdep enabled (although I triggered a locked warning unrelated to
this, with the text_mutex and module_mutex, but I'm hoping my tree has
the fixes for that).

Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

Hmm, does this mean we can remove the IDT switching in the NMI handler
as well?

-- Steve


>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> ---
> arch/x86/entry/entry_64.S | 46 ++--------------------------------------------
> 1 file changed, 2 insertions(+), 44 deletions(-)
>
> --- a/arch/x86/entry/entry_64.S
> +++ b/arch/x86/entry/entry_64.S
> @@ -68,44 +68,6 @@ END(native_usergs_sysret64)
> .endm
>
> /*
> - * When dynamic function tracer is enabled it will add a breakpoint
> - * to all locations that it is about to modify, sync CPUs, update
> - * all the code, sync CPUs, then remove the breakpoints. In this time
> - * if lockdep is enabled, it might jump back into the debug handler
> - * outside the updating of the IST protection. (TRACE_IRQS_ON/OFF).
> - *
> - * We need to change the IDT table before calling TRACE_IRQS_ON/OFF to
> - * make sure the stack pointer does not get reset back to the top
> - * of the debug stack, and instead just reuses the current stack.
> - */
> -#if defined(CONFIG_DYNAMIC_FTRACE) && defined(CONFIG_TRACE_IRQFLAGS)
> -
> -.macro TRACE_IRQS_OFF_DEBUG
> - call debug_stack_set_zero
> - TRACE_IRQS_OFF
> - call debug_stack_reset
> -.endm
> -
> -.macro TRACE_IRQS_ON_DEBUG
> - call debug_stack_set_zero
> - TRACE_IRQS_ON
> - call debug_stack_reset
> -.endm
> -
> -.macro TRACE_IRQS_IRETQ_DEBUG
> - btl $9, EFLAGS(%rsp) /* interrupts off? */
> - jnc 1f
> - TRACE_IRQS_ON_DEBUG
> -1:
> -.endm
> -
> -#else
> -# define TRACE_IRQS_OFF_DEBUG TRACE_IRQS_OFF
> -# define TRACE_IRQS_ON_DEBUG TRACE_IRQS_ON
> -# define TRACE_IRQS_IRETQ_DEBUG TRACE_IRQS_IRETQ
> -#endif
> -
> -/*
> * 64-bit SYSCALL instruction entry. Up to 6 arguments in registers.
> *
> * This is the only entry point used for 64-bit system calls. The
> @@ -879,11 +841,7 @@ apicinterrupt IRQ_WORK_VECTOR irq_work
> GET_CR2_INTO(%rdx); /* can clobber %rax */
> .endif
>
> - .if \shift_ist != -1
> - TRACE_IRQS_OFF_DEBUG /* reload IDT in case of recursion */
> - .else
> TRACE_IRQS_OFF
> - .endif
>
> .if \paranoid == 0
> testb $3, CS(%rsp)
> @@ -1292,7 +1250,7 @@ END(paranoid_entry)
> ENTRY(paranoid_exit)
> UNWIND_HINT_REGS
> DISABLE_INTERRUPTS(CLBR_ANY)
> - TRACE_IRQS_OFF_DEBUG
> + TRACE_IRQS_OFF
>
> /* Handle GS depending on FSGSBASE availability */
> ALTERNATIVE "jmp .Lparanoid_exit_checkgs", "nop",X86_FEATURE_FSGSBASE
> @@ -1312,7 +1270,7 @@ ENTRY(paranoid_exit)
> jmp .Lparanoid_exit_restore
>
> .Lparanoid_exit_no_swapgs:
> - TRACE_IRQS_IRETQ_DEBUG
> + TRACE_IRQS_IRETQ
> /* Always restore stashed CR3 value (see paranoid_entry) */
> RESTORE_CR3 scratch_reg=%rbx save_reg=%r14
>
>

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