linux-kernel - Re: [PATCH RFC 1/2] x86/apic: Do not make an exception for PIC_CASCADE_IR when marking legacy irqs in irq

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Date:   Thu, 18 Mar 2021 11:10:07 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>, x86@...nel.org
Cc:     Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC 1/2] x86/apic: Do not make an exception for PIC_CASCADE_IR when marking legacy irqs in irq_matrix

On Thu, Mar 18 2021 at 09:29, Vitaly Kuznetsov wrote:
> Thomas Gleixner <tglx@...utronix.de> writes:
>> Out of paranoia I'd rather ignore that IO/APIC pin completely if it
>> claims to be IRQ2. I assume there is no device connected to it at all,
>> right?
>
> The original issue was observed on Amazon's r5d.xlarge instance
> type. Your assumption seems to be correct, I don't see any device on
> IRQ2.
>
>>
>> Can you please provide a dmesg with apic=verbose on the command line?
>>
>
> Here you go, attached.

> [    0.931305] init IO_APIC IRQs
> [    0.931312] IOAPIC[0]: Preconfigured routing entry (0-0 -> IRQ 0 Level:0 ActiveLow:0)
> [    0.931316] IOAPIC[0]: Preconfigured routing entry (0-1 -> IRQ 1 Level:0 ActiveLow:0)

There you go:

> [    0.931320] IOAPIC[0]: Preconfigured routing entry (0-2 -> IRQ 2 Level:0 ActiveLow:0)

Yet another virtualization feature :)

Thanks,

        tglx