linux-kernel - Re: [PATCH] x86/irq: Preserve vector in orig

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Message-ID: <9f351750-f652-f9c5-ca79-fc90273ee3c8@amazon.com>
Date:   Wed, 26 Aug 2020 22:09:49 +0200
From:   Alexander Graf <graf@...zon.com>
To:     Thomas Gleixner <tglx@...utronix.de>, X86 ML <x86@...nel.org>
CC:     Andy Lutomirski <luto@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Andrew Cooper <andrew.cooper3@...rix.com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Alexandre Chartre <alexandre.chartre@...cle.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        "Will Deacon" <will@...nel.org>,
        Tom Lendacky <thomas.lendacky@....com>,
        Wei Liu <wei.liu@...nel.org>,
        Michael Kelley <mikelley@...rosoft.com>,
        Jason Chen CJ <jason.cj.chen@...el.com>,
        Zhao Yakui <yakui.zhao@...el.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Avi Kivity <avi@...lladb.com>,
        "Herrenschmidt, Benjamin" <benh@...zon.com>, <robketr@...zon.de>,
        <amos@...lladb.com>, Brian Gerst <brgerst@...il.com>,
        <stable@...r.kernel.org>
Subject: Re: [PATCH] x86/irq: Preserve vector in orig_ax for APIC code



On 26.08.20 20:53, Thomas Gleixner wrote:
> 
> 
> On Wed, Aug 26 2020 at 20:30, Thomas Gleixner wrote:
>> And it does not solve the issue that we abuse orig_ax which Andy
>> mentioned.
> 
> Ha! After staring some more, it's not required at all, which is the most
> elegant solution.
> 
> The vector check is pointless in that condition because there is never a
> condition where an interrupt is moved from vector A to vector B on the
> same CPU.
> 
> That's a left over from the old allocation model which supported
> multi-cpu affinities, but this was removed as it just created trouble
> for no real benefit.
> 
> Today the effective affinity which is a single CPU out of the requested
> affinity. If an affinity mask change still contains the current target
> CPU then there is no move happening at all. It just stays on that vector
> on that CPU.
> 
> Thanks,
> 
>          tglx
> ---
> 
> --- a/arch/x86/kernel/apic/vector.c
> +++ b/arch/x86/kernel/apic/vector.c
> @@ -909,7 +909,7 @@ void send_cleanup_vector(struct irq_cfg
>                  __send_cleanup_vector(apicd);
>   }
> 
> -static void __irq_complete_move(struct irq_cfg *cfg, unsigned vector)
> +void irq_complete_move(struct irq_cfg *cfg)
>   {
>          struct apic_chip_data *apicd;
> 
> @@ -917,15 +917,10 @@ static void __irq_complete_move(struct i
>          if (likely(!apicd->move_in_progress))
>                  return;
> 
> -       if (vector == apicd->vector && apicd->cpu == smp_processor_id())
> +       if (apicd->cpu == smp_processor_id())
>                  __send_cleanup_vector(apicd);
>   }
> 
> -void irq_complete_move(struct irq_cfg *cfg)
> -{
> -       __irq_complete_move(cfg, ~get_irq_regs()->orig_ax);
> -}
> -
>   /*
>    * Called from fixup_irqs() with @desc->lock held and interrupts disabled.
>    */
> 


As expected, this also fixes the issue at hand. Do you want to send a 
real patch? :)

Tested-by: Alexander Graf <graf@...zon.com>


Alex



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