netdev - Re: [PATCH mlx5-next v8 1/4] PCI: Add a sysfs file to change the MSI-X table size of SR-IOV VFs

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Date:   Fri, 2 Apr 2021 19:24:26 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Leon Romanovsky <leon@...nel.org>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>,
        Saeed Mahameed <saeedm@...dia.com>,
        Jason Gunthorpe <jgg@...dia.com>,
        Alexander Duyck <alexander.duyck@...il.com>,
        Jakub Kicinski <kuba@...nel.org>, linux-pci@...r.kernel.org,
        linux-rdma@...r.kernel.org, netdev@...r.kernel.org,
        Don Dutile <ddutile@...hat.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        "David S . Miller" <davem@...emloft.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH mlx5-next v8 1/4] PCI: Add a sysfs file to change the
 MSI-X table size of SR-IOV VFs

Possible subject, since this adds *two* files, not just "a file":

  PCI/IOV: Add sysfs MSI-X vector assignment interface

On Sun, Mar 14, 2021 at 02:42:53PM +0200, Leon Romanovsky wrote:
> A typical cloud provider SR-IOV use case is to create many VFs for use by
> guest VMs. The VFs may not be assigned to a VM until a customer requests a
> VM of a certain size, e.g., number of CPUs. A VF may need MSI-X vectors
> proportional to the number of CPUs in the VM, but there is no standard way
> to change the number of MSI-X vectors supported by a VF.
> ...

> +#ifdef CONFIG_PCI_MSI
> +static ssize_t sriov_vf_msix_count_store(struct device *dev,
> +					 struct device_attribute *attr,
> +					 const char *buf, size_t count)
> +{
> +	struct pci_dev *vf_dev = to_pci_dev(dev);
> +	struct pci_dev *pdev = pci_physfn(vf_dev);
> +	int val, ret;
> +
> +	ret = kstrtoint(buf, 0, &val);
> +	if (ret)
> +		return ret;
> +
> +	if (val < 0)
> +		return -EINVAL;
> +
> +	device_lock(&pdev->dev);
> +	if (!pdev->driver || !pdev->driver->sriov_set_msix_vec_count) {
> +		ret = -EOPNOTSUPP;
> +		goto err_pdev;
> +	}
> +
> +	device_lock(&vf_dev->dev);
> +	if (vf_dev->driver) {
> +		/*
> +		 * A driver is already attached to this VF and has configured
> +		 * itself based on the current MSI-X vector count. Changing
> +		 * the vector size could mess up the driver, so block it.
> +		 */
> +		ret = -EBUSY;
> +		goto err_dev;
> +	}
> +
> +	ret = pdev->driver->sriov_set_msix_vec_count(vf_dev, val);
> +
> +err_dev:
> +	device_unlock(&vf_dev->dev);
> +err_pdev:
> +	device_unlock(&pdev->dev);
> +	return ret ? : count;
> +}
> +static DEVICE_ATTR_WO(sriov_vf_msix_count);
> +
> +static ssize_t sriov_vf_total_msix_show(struct device *dev,
> +					struct device_attribute *attr,
> +					char *buf)
> +{
> +	struct pci_dev *pdev = to_pci_dev(dev);
> +	u32 vf_total_msix = 0;
> +
> +	device_lock(dev);
> +	if (!pdev->driver || !pdev->driver->sriov_get_vf_total_msix)
> +		goto unlock;
> +
> +	vf_total_msix = pdev->driver->sriov_get_vf_total_msix(pdev);
> +unlock:
> +	device_unlock(dev);
> +	return sysfs_emit(buf, "%u\n", vf_total_msix);
> +}
> +static DEVICE_ATTR_RO(sriov_vf_total_msix);

Can you reverse the order of sriov_vf_total_msix_show() and
sriov_vf_msix_count_store()?  Currently we have:

  VF stuff (msix_count_store)
  PF stuff (total_msix)
  more VF stuff related to the above (vf_dev_attrs, are_visible)

so the total_msix bit is mixed in the middle.

> +#endif
> +
> +static struct attribute *sriov_vf_dev_attrs[] = {
> +#ifdef CONFIG_PCI_MSI
> +	&dev_attr_sriov_vf_msix_count.attr,
> +#endif
> +	NULL,
> +};
> +
> +static umode_t sriov_vf_attrs_are_visible(struct kobject *kobj,
> +					  struct attribute *a, int n)
> +{
> +	struct device *dev = kobj_to_dev(kobj);
> +	struct pci_dev *pdev = to_pci_dev(dev);
> +
> +	if (!pdev->is_virtfn)
> +		return 0;
> +
> +	return a->mode;
> +}
> +
> +const struct attribute_group sriov_vf_dev_attr_group = {
> +	.attrs = sriov_vf_dev_attrs,
> +	.is_visible = sriov_vf_attrs_are_visible,
> +};
> +
>  int pci_iov_add_virtfn(struct pci_dev *dev, int id)
>  {
>  	int i;
> @@ -400,18 +487,21 @@ static DEVICE_ATTR_RO(sriov_stride);
>  static DEVICE_ATTR_RO(sriov_vf_device);
>  static DEVICE_ATTR_RW(sriov_drivers_autoprobe);
> 
> -static struct attribute *sriov_dev_attrs[] = {
> +static struct attribute *sriov_pf_dev_attrs[] = {

This and the related sriov_pf_attrs_are_visible change below are nice.
Would you mind splitting them to a preliminary patch, since they
really aren't related to the concept of *this* patch?

>  	&dev_attr_sriov_totalvfs.attr,
>  	&dev_attr_sriov_numvfs.attr,
>  	&dev_attr_sriov_offset.attr,
>  	&dev_attr_sriov_stride.attr,
>  	&dev_attr_sriov_vf_device.attr,
>  	&dev_attr_sriov_drivers_autoprobe.attr,
> +#ifdef CONFIG_PCI_MSI
> +	&dev_attr_sriov_vf_total_msix.attr,
> +#endif
>  	NULL,
>  };
> 
> -static umode_t sriov_attrs_are_visible(struct kobject *kobj,
> -				       struct attribute *a, int n)
> +static umode_t sriov_pf_attrs_are_visible(struct kobject *kobj,
> +					  struct attribute *a, int n)
>  {
>  	struct device *dev = kobj_to_dev(kobj);
> 
> @@ -421,9 +511,9 @@ static umode_t sriov_attrs_are_visible(struct kobject *kobj,
>  	return a->mode;
>  }
> 
> -const struct attribute_group sriov_dev_attr_group = {
> -	.attrs = sriov_dev_attrs,
> -	.is_visible = sriov_attrs_are_visible,
> +const struct attribute_group sriov_pf_dev_attr_group = {
> +	.attrs = sriov_pf_dev_attrs,
> +	.is_visible = sriov_pf_attrs_are_visible,
>  };