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SubjectRe: [patch 13/16] x86/entry: Move irqflags and context tracking to C for simple idtentries
On Wed, Feb 26, 2020 at 09:09:34AM -0800, Andy Lutomirski wrote:
>
>
> > 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.

Oh right...

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