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Subject: Re: [PATCH] x86/irq: Preserve vector in orig_ax for APIC code
To:     Thomas Gleixner <tglx@linutronix.de>, X86 ML <x86@kernel.org>
CC:     Andy Lutomirski <luto@kernel.org>,
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References: <20200826115357.3049-1-graf@amazon.com>
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 <873649utm4.fsf@nanos.tec.linutronix.de>
From:   Alexander Graf <graf@amazon.com>
Message-ID: <9f351750-f652-f9c5-ca79-fc90273ee3c8@amazon.com>
Date:   Wed, 26 Aug 2020 22:09:49 +0200
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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 =3D=3D apicd->vector && apicd->cpu =3D=3D smp_processo=
r_id())
> +       if (apicd->cpu =3D=3D 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 disabl=
ed.
>    */
> =


As expected, this also fixes the issue at hand. Do you want to send a =

real patch? :)

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


Alex


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