linux-kernel - Re: [PATCH 5/5] x86/kvm: Add KVM_FEATURE_MSI_EXT_DEST

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Date:   Sun, 11 Oct 2020 22:15:13 +0100
From:   David Woodhouse <dwmw2@...radead.org>
To:     Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org
CC:     kvm <kvm@...r.kernel.org>, Paolo Bonzini <pbonzini@...hat.com>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 5/5] x86/kvm: Add KVM_FEATURE_MSI_EXT_DEST_ID



On 11 October 2020 18:12:08 BST, Thomas Gleixner <tglx@...utronix.de> wrote:
>On Sat, Oct 10 2020 at 12:58, David Woodhouse wrote:
>> On 10 October 2020 12:44:10 BST, Thomas Gleixner <tglx@...utronix.de>
>wrote:
>>>On Sat, Oct 10 2020 at 11:06, David Woodhouse wrote:
>
>>>> The IRQ remapping drivers already plug into the device-add notifier
>>>> and can fill in the appropriate MSI domain just like they do¹ for
>>>> PCI and ACPI devices.
>>>> Using platform_add_bundle() for HPET looks trivial enough; I'll
>have
>>>> a play with that and then do IOAPIC too if/when the initialisation
>>>> order and hotplug handling all works out OK to install the correct
>>>> msi_domain.
>>>
>>> Yes, I was wondering about that when I made PCI at least use that
>>> mechanism, but had not had time to actually look at it.
>>
>> Yeah. There's some muttering to be done for HPET about whether it's
>> *its* MSI domain or whether it's the parent domain. But I'll have a
>> play. I think we'll be able to drop the whole
>> irq_remapping_get_irq_domain() thing.
>
>That would be really nice.

I can make it work for HPET if I fix up the point at which the IRQ remapping code registers a notifier on the platform bus. (At IRQ remap setup time is too early; when it registers the PCI bus notifier is too late.)

IOAPIC is harder though as the platform bus doesn't even exist that early. Maybe an early platform bus is possible but it would have to turn out particularly simple to do, or I'd need to find another use case too, to justify it. Will continue to play....

>> Either way, it's a separate cleanup and the 15-bit APIC ID series I
>> posted yesterday should be fine as it is.
>
>I go over it in the next days once more and stick it into my devel tree
>until rc1. Need to get some conflicts sorted with that Device MSI
>stuff.

While playing with HPET I noticed I need s/CONFIG_PCI_MSI/CONFIG_IRQ_GENERIC_MSI/ where the variables are declared at the top of msi.c to match the change I made later on. Can post v3 of the series or you can silently fix it up as you go; please advise.

-- 
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