On Thu, 2020-10-08 at 14:40 +0200, Thomas Gleixner wrote:
> Subject: x86/iommu: Make interrupt remapping more robust
> From: Thomas Gleixner <tglx@linutronix.de>
> Date: Thu, 08 Oct 2020 14:09:44 +0200
> 
> Needs to be split into pieces and cover PCI proper. Right now PCI gets a
> NULL pointer assigned which makes it explode at the wrong place
> later. Also hyperv iommu wants some love.
> 
> NOT-Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> ---
>  arch/x86/kernel/apic/io_apic.c      |    4 +++-
>  arch/x86/kernel/apic/msi.c          |   24 ++++++++++++++----------
>  drivers/iommu/amd/iommu.c           |    6 +++---
>  drivers/iommu/intel/irq_remapping.c |    4 ++--
>  4 files changed, 22 insertions(+), 16 deletions(-)
> 
> --- a/arch/x86/kernel/apic/io_apic.c
> +++ b/arch/x86/kernel/apic/io_apic.c
> @@ -2300,7 +2300,9 @@ static int mp_irqdomain_create(int ioapi
>         info.type = X86_IRQ_ALLOC_TYPE_IOAPIC_GET_PARENT;
>         info.devid = mpc_ioapic_id(ioapic);
>         parent = irq_remapping_get_irq_domain(&info);
> -       if (!parent)
> +       if (IS_ERR(parent))
> +               return PTR_ERR(parent);
> +       else if (!parent)
>                 parent = x86_vector_domain;
>         else
>                 name = "IO-APIC-IR";
> --- a/arch/x86/kernel/apic/msi.c
> +++ b/arch/x86/kernel/apic/msi.c
> @@ -415,9 +415,9 @@ static struct msi_domain_info hpet_msi_d
>  struct irq_domain *hpet_create_irq_domain(int hpet_id)
>  {
>         struct msi_domain_info *domain_info;
> +       struct fwnode_handle *fn = NULL;
>         struct irq_domain *parent, *d;
>         struct irq_alloc_info info;
> -       struct fwnode_handle *fn;
>  
>         if (x86_vector_domain == NULL)
>                 return NULL;
> @@ -432,25 +432,29 @@ struct irq_domain *hpet_create_irq_domai
>         init_irq_alloc_info(&info, NULL);
>         info.type = X86_IRQ_ALLOC_TYPE_HPET_GET_PARENT;
>         info.devid = hpet_id;
> +
>         parent = irq_remapping_get_irq_domain(&info);
> -       if (parent == NULL)
> +       if (IS_ERR(parent))
> +               goto fail;
> +       else if (!parent)
>                 parent = x86_vector_domain;
>         else
>                 hpet_msi_controller.name = "IR-HPET-MSI";

Hrm... this is the '-ENODEV changes' that you wanted me to pick up,
right?

I confess I don't like it very much.

I'd much prefer to be able to use a generic foo_get_parent_irq_domain()
function which just returns an answer or an error.

Definitely none of this "if it returns NULL, caller fills it in for
themselves with some magic global because we're special".

And I don't much like abusing the irq_alloc_info for this either. I
didn't like the irq_alloc_info very much in its *original* use cases,
for actually allocating IRQs. Abusing it for this is worse.

I'm more than happy to start digging into this, but once I do I fear
I'm not going to stop until HPET and IOAPIC don't know *anything* about
whether they're behind IR or not.

And yes, I know that IOAPIC has a different EOI method for IR but
AFAICT that's *already* hosed for Hyper-V because it doesn't *really*
do remapping and so the RTEs *can* change there to move interrupts
around. There's more differences between ioapic_ack_level() and
ioapic_ir_ack_level() than the erratum workaround and whether we use
data->entry.vector... aren't there?

For the specific case you were targeting with this patch, you already
successfully persuaded me it should never happen, and there's a WARN_ON
which would trigger if it ever does (with too many CPUs in the system).

Let's come back and tackle this can of worms in a separate cleanup
series.