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Date: Wed, 26 Feb 2020 18:17:06 +0100 From: Frederic Weisbecker <frederic@...nel.org> To: Andy Lutomirski <luto@...capital.net> Cc: Peter Zijlstra <peterz@...radead.org>, Thomas Gleixner <tglx@...utronix.de>, LKML <linux-kernel@...r.kernel.org>, x86@...nel.org, Steven Rostedt <rostedt@...dmis.org>, Brian Gerst <brgerst@...il.com>, Juergen Gross <JGross@...e.com>, Paolo Bonzini <pbonzini@...hat.com>, Arnd Bergmann <arnd@...db.de> Subject: Re: [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@...nel.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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