Re: [PATCH v4 13/17] dmaengine: idxd: ims setup for the vdcm

[Thomas Gleixner]

On Fri, Oct 30 2020 at 11:52, Dave Jiang wrote:
> Add setup for IMS enabling for the mediated device.

....

> Register with the irq bypass manager in order to allow the IMS interrupt be
> injected into the guest and bypass the host.

Why is this part of the patch which adds IMS support? This are two
completely different things.

Again, Documentation/process/submitting-patches.rst is very clear about
this:
        Solve only one problem per patch.

You want me to review the IMS related things. Why are you mixing that
completely unrelated bypass stuff to it?

> +void vidxd_free_ims_entries(struct vdcm_idxd *vidxd)
> +{
> +	struct irq_domain *irq_domain;
> +	struct mdev_device *mdev = vidxd->vdev.mdev;
> +	struct device *dev = mdev_dev(mdev);
> +	int i;
> +
> +	for (i = 0; i < VIDXD_MAX_MSIX_VECS; i++)
> +		vidxd->irq_entries[i].entry = NULL;

See below.

> +	irq_domain = dev_get_msi_domain(dev);
> +	if (irq_domain)
> +		msi_domain_free_irqs(irq_domain, dev);
> +	else
> +		dev_warn(dev, "No IMS irq domain.\n");

How is the code even getting to this point if the domain allocation
failed in the first place?

> +int vidxd_setup_ims_entries(struct vdcm_idxd *vidxd)
> +{
> +	struct irq_domain *irq_domain;
> +	struct idxd_device *idxd = vidxd->idxd;
> +	struct mdev_device *mdev = vidxd->vdev.mdev;
> +	struct device *dev = mdev_dev(mdev);
> +	int vecs = VIDXD_MAX_MSIX_VECS - 1;

Some sensible comment about the -1 is missing here.

> +	struct msi_desc *entry;
> +	struct ims_irq_entry *irq_entry;
> +	int rc, i = 0;
> +
> +	irq_domain = idxd->ims_domain;
> +	dev_set_msi_domain(dev, irq_domain);
> +	rc = msi_domain_alloc_irqs(irq_domain, dev, vecs);
> +	if (rc < 0)
> +		return rc;
> +
> +	for_each_msi_entry(entry, dev) {
> +		irq_entry = &vidxd->irq_entries[i];
> +		irq_entry->vidxd = vidxd;
> +		irq_entry->entry = entry;

What's the business with storing the MSI entry here? Just to do this:

       ims_idx = vidxd->irq_entries[vidx - 1].entry->device_msi.hwirq;

and this:

      if (vidxd->irq_entries[i].entry->device_msi.hwirq == handle) {

What's wrong with storing the hardware interrupt index right here
instead of handing that pointer around? The usage sites have no reason
to know about the entry itself.

> +		irq_entry->id = i;

Again, what is the point of storing the array offset in the array slot?
If it _is_ useful then adding a comment is not too much asked for.

So the place I found which uses it cannot compute the index obviously,
but this:

        vidxd_send_interrupt(irq_entry->vidxd, irq_entry->id + 1);

is again just voodoo programming. Why can't you just provide a data set
which contains data ready for consumption at the usage site?

> diff --git a/kernel/irq/msi.c b/kernel/irq/msi.c
> index c7e47c26cd90..89cf60a30803 100644
> --- a/kernel/irq/msi.c
> +++ b/kernel/irq/msi.c
> @@ -536,6 +536,7 @@ int msi_domain_alloc_irqs(struct irq_domain *domain, struct device *dev,
>  
>  	return ops->domain_alloc_irqs(domain, dev, nvec);
>  }
> +EXPORT_SYMBOL(msi_domain_alloc_irqs);

Sigh... This want's to be a preperatory patch and the export wants to be
EXPORT_SYMBOL_GPL
  
Thanks,

        tglx