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SubjectRe: [patch 13/16] x86/entry: Move irqflags and context tracking to C for simple idtentries
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> On Feb 26, 2020, at 9:05 AM, Frederic Weisbecker <frederic@kernel.org> wrote:
>
> On Wed, Feb 26, 2020 at 09:05:38AM +0100, Peter Zijlstra wrote:
>>> On Tue, Feb 25, 2020 at 11:33:34PM +0100, Thomas Gleixner wrote:
>>>
>>> --- a/arch/x86/include/asm/idtentry.h
>>> +++ b/arch/x86/include/asm/idtentry.h
>>> @@ -7,14 +7,31 @@
>>>
>>> #ifndef __ASSEMBLY__
>>>
>>> +#ifdef CONFIG_CONTEXT_TRACKING
>>> +static __always_inline void enter_from_user_context(void)
>>> +{
>>> + CT_WARN_ON(ct_state() != CONTEXT_USER);
>>> + user_exit_irqoff();
>>> +}
>>> +#else
>>> +static __always_inline void enter_from_user_context(void) { }
>>> +#endif
>>> +
>>> /**
>>> * idtentry_enter - Handle state tracking on idtentry
>>> * @regs: Pointer to pt_regs of interrupted context
>>> *
>>> - * Place holder for now.
>>> + * Invokes:
>>> + * - The hardirq tracer to keep the state consistent as low level ASM
>>> + * entry disabled interrupts.
>>> + *
>>> + * - Context tracking if the exception hit user mode
>>> */
>>> static __always_inline void idtentry_enter(struct pt_regs *regs)
>>> {
>>> + trace_hardirqs_off();
>>> + if (user_mode(regs))
>>> + enter_from_user_context();
>>> }
>>
>> So:
>>
>> asm_exc_int3
>> exc_int3
>> idtentry_enter()
>> enter_from_user_context
>> if (context_tracking_enabled())
>>
>> poke_int3_handler();
>>
>> Is, AFAICT, completely buggered.
>>
>> You can't have a static_branch before the poke_int3_handler that deals
>> with text_poke.
>
> #BP is treated like an NMI in your patchset IIRC?
> In that case and since that implies we can't schedule, we can remove
> the call to context tracking there once we have nmi_enter()/nmi_exit()
> called unconditionally.

int3 from user mode can send signals. This has better be able to schedule by the time it hits prepare_exit_to_usermode.
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