linux-kernel - Re: x86/apic: MSI address malformed for "flat" driver

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Message-ID: <27bccfd2-0ede-cd3a-2717-741d3dffebdf@lynx.com>
Date:   Mon, 10 Sep 2018 23:02:46 -0700
From:   Cyril Novikov <cnovikov@...x.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Philipp Eppelt <philipp.eppelt@...nkonzept.com>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: x86/apic: MSI address malformed for "flat" driver

On 9/7/2018 12:11 PM, Thomas Gleixner wrote:
> On Thu, 6 Sep 2018, Philipp Eppelt wrote:
>>
>> The "flat" driver defines the MSI addressing scheme to be used as
>> logical addressing in flat mode. The MSI msg address is composed
>> accordingly, but sets MSI_ADDR_REDIRECTION_CPU which is a zero at bit[3].
> 
> Correct. That's what it means:
> 
>    * When RH is 0, the interrupt is directed to the processor listed in the
>      Destination ID field.
> 
> So for DM:
> 
>    * If RH is 0, then the DM bit is ignored and the message is sent ahead
>      independent of whether the physical or logical destination mode is
>      used.
> 
> which is means that the delivery does not do any magic redirections,
> because the Redirection Hint is off. If RH is set, then the delivery can
> redirect according to the rules in the DM section. We are not using that
> because we want targeted single CPU delivery.
> 
> The interpretation of the DID field is purely depending on the local APIC
> itself by matching the APIC ID against the DID field. And the local APIC ID
> of CPU0 is 1 << 0, i.e. 0x1 which matches the MSI message you see.

I believe you are wrong here and the local APIC ID of CPU0 is 0.

processor       : 0
vendor_id       : GenuineIntel
...
physical id     : 0
siblings        : 8
core id         : 0
cpu cores       : 4
apicid          : 0

The fact that the code works means that DM is not ignored when RH is 0. 
In other words, RH=0 DM=1 means logical destination mode.

--
Cyril