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

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Date:   Tue, 13 Oct 2020 11:28:58 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     David Woodhouse <dwmw2@...radead.org>, x86@...nel.org,
        Marc Zyngier <maz@...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 Tue, Oct 13 2020 at 08:52, David Woodhouse wrote:
> On Tue, 2020-10-13 at 00:13 +0200, Thomas Gleixner wrote:
> +       dom = irq_find_matching_fwspec(fwspec, DOMAIN_BUS_IR);
> +       if (dom)
> +               return IS_ERR(dom) ? NULL : dom;
> +
> +       return x86_vector_domain;
> +}
>
> Ick. There's no need for that.
>
> Eliminating that awful "if not found then slip the x86_vector_domain in
> as a special case" was the whole *point* of using
> irq_find_matching_fwspec() in the first place.

The point was to get rid of irq_remapping_get_irq_domain().

And TBH,

        if (apicid_valid(32768))

is just another way to slip the vector domain in. It's just differently
awful.

Having an explicit answer from the search for IR:

    - Here is the domain
    - Your device is not registered properly
    - IR not enabled or not supported

is way more obvious than the above disguised is_remapping_enabled()
check.

Thanks,

        tglx