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

On Fri, Apr 02, 2021 at 07:24:26PM -0500, Bjorn Helgaas wrote:

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

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

Sure

On Sun, Mar 14, 2021 at 02:42:53PM +0200, Leon Romanovsky wrote:

quoted

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.
...

quoted

+#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.

No problem, I'll do.

quoted

+#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?

I don't think so, that prepatch will have only two lines of renames
from sriov_dev_attrs to be sriov_pf_dev_attrs. It is not worth the
hassle.

Thanks

quoted

 	&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,
 };