Re: [PATCH 10/13] x86/irq: Limit IOAPIC and MSI domains' affinity without IR

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On Wed, 2020-10-07 at 16:05 +0200, Thomas Gleixner wrote:
> On Wed, Oct 07 2020 at 14:08, David Woodhouse wrote:
> > On 7 October 2020 13:59:00 BST, Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote:
> > > On Wed, Oct 07 2020 at 08:48, David Woodhouse wrote:
> > > > To fix *that* case, we really do need the whole series giving us per-
> > > > domain restricted affinity, and to use it for those MSIs/IOAPICs that
> > > > the IRQ remapping doesn't cover.
> > > 
> > > Which do not exist today.
> > 
> > Sure. But at patch 10/13 into this particular patch series, it *does*
> > exist.
> 
> As I told you before: Your ordering is wrong. We do not introduce bugs
> first and then fix them later ....

I didn't introduce that bug; it's been there for years. Fixing it
properly requires per-irqdomain affinity limits.

There's a cute little TODO at least in the Intel irq-remapping driver,
noting that we should probably check if there are any IOAPICs that
aren't in the scope of any DRHD at all. But that's all.

If it happens, I think we'll end up doing the right thing and
instantiating a non-IR IOAPIC domain for it, and if we *don't* have any
CPU with an APIC ID above... (checks notes)... 7 ... then it'll just
about work out. Over 7 and we're screwed (because logical mode; see
also https://git.infradead.org/users/dwmw2/linux.git/commit/429f0c33f
for a straw man but that's getting even further down the rabbit hole)

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