[PATCH mlx5-next v7 1/4] PCI: Add a sysfs file to change the MSI-X table size of SR-IOV VFs

Leon Romanovsky
2021-03-01T07:56:26Z

From: Leon Romanovsky <leonro@nvidia.com>

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.

Some Mellanox ConnectX devices support dynamic assignment of MSI-X vectors
to SR-IOV VFs. This can be done by the PF driver after VFs are enabled,
and it can be done without affecting VFs that are already in use. The
hardware supports a limited pool of MSI-X vectors that can be assigned to
the PF or to individual VFs. This is device-specific behavior that
requires support in the PF driver.

Add a read-only "sriov_vf_total_msix" sysfs file for the PF and a writable
"sriov_vf_msix_count" file for each VF. Management software may use these
to learn how many MSI-X vectors are available and to dynamically assign
them to VFs before the VFs are passed through to a VM.

If the PF driver implements the ->sriov_get_vf_total_msix() callback,
"sriov_vf_total_msix" contains the total number of MSI-X vectors available
for distribution among VFs.

If no driver is bound to the VF, writing "N" to "sriov_vf_msix_count" uses
the PF driver ->sriov_set_msix_vec_count() callback to assign "N" MSI-X
vectors to the VF. When a VF driver subsequently reads the MSI-X Message
Control register, it will see the new Table Size "N".

Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
---
Documentation/ABI/testing/sysfs-bus-pci | 29 +++++++
drivers/pci/iov.c | 102 ++++++++++++++++++++++--
drivers/pci/pci-sysfs.c | 3 +-
drivers/pci/pci.h | 3 +-
include/linux/pci.h | 8 ++
5 files changed, 137 insertions(+), 8 deletions(-)

diff --git a/Documentation/ABI/testing/sysfs-bus-pci b/Documentation/ABI/testing/sysfs-bus-pci
index 25c9c39770c6..ebabd0d2ae88 100644
--- a/Documentation/ABI/testing/sysfs-bus-pci
+++ b/Documentation/ABI/testing/sysfs-bus-pci
@@ -375,3 +375,32 @@ Description:
The value comes from the PCI kernel device state and can be one
of: "unknown", "error", "D0", D1", "D2", "D3hot", "D3cold".
The file is read only.
+
+What: /sys/bus/pci/devices/.../sriov_vf_total_msix
+Date: January 2021
+Contact: Leon Romanovsky <leonro@nvidia.com>
+Description:
+ This file is associated with a SR-IOV PF. It contains the
+ total number of MSI-X vectors available for assignment to
+ all VFs associated with PF. It will zero if the device
+ doesn't support this functionality. For supported devices,
+ the value will be constant and won't be changed after MSI-X
+ vectors assignment.
+
+What: /sys/bus/pci/devices/.../sriov_vf_msix_count
+Date: January 2021
+Contact: Leon Romanovsky <leonro@nvidia.com>
+Description:
+ This file is associated with a SR-IOV VF. It allows
+ configuration of the number of MSI-X vectors for the VF. This
+ allows devices that have a global pool of MSI-X vectors to
+ optimally divide them between VFs based on VF usage.
+
+ The values accepted are:
+ * > 0 - this number will be reported as the Table Size in the
+ VF's MSI-X capability
+ * < 0 - not valid
+ * = 0 - will reset to the device default value
+
+ The file is writable if the PF is bound to a driver that
+ implements ->sriov_set_msix_vec_count().
diff --git a/drivers/pci/iov.c b/drivers/pci/iov.c
index 4afd4ee4f7f0..9bf6f52ad4d8 100644
--- a/drivers/pci/iov.c
+++ b/drivers/pci/iov.c
@@ -31,6 +31,7 @@ int pci_iov_virtfn_devfn(struct pci_dev *dev, int vf_id)
return (dev->devfn + dev->sriov->offset +
dev->sriov->stride * vf_id) & 0xff;
}
+EXPORT_SYMBOL_GPL(pci_iov_virtfn_devfn);

/*
* Per SR-IOV spec sec 3.3.10 and 3.3.11, First VF Offset and VF Stride may
@@ -157,6 +158,92 @@ int pci_iov_sysfs_link(struct pci_dev *dev,
return rc;
}

+#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);
+#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[] = {
&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,
};

int __weak pcibios_sriov_enable(struct pci_dev *pdev, u16 num_vfs)
diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
index f8afd54ca3e1..a6b8fbbba6d2 100644
--- a/drivers/pci/pci-sysfs.c
+++ b/drivers/pci/pci-sysfs.c
@@ -1567,7 +1567,8 @@ static const struct attribute_group *pci_dev_attr_groups[] = {
&pci_dev_attr_group,
&pci_dev_hp_attr_group,
#ifdef CONFIG_PCI_IOV
- &sriov_dev_attr_group,
+ &sriov_pf_dev_attr_group,
+ &sriov_vf_dev_attr_group,
#endif
&pci_bridge_attr_group,
&pcie_dev_attr_group,
diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
index ef7c4661314f..afb87b917f07 100644
--- a/drivers/pci/pci.h
+++ b/drivers/pci/pci.h
@@ -501,7 +501,8 @@ void pci_iov_update_resource(struct pci_dev *dev, int resno);
resource_size_t pci_sriov_resource_alignment(struct pci_dev *dev, int resno);
void pci_restore_iov_state(struct pci_dev *dev);
int pci_iov_bus_range(struct pci_bus *bus);
-extern const struct attribute_group sriov_dev_attr_group;
+extern const struct attribute_group sriov_pf_dev_attr_group;
+extern const struct attribute_group sriov_vf_dev_attr_group;
#else
static inline int pci_iov_init(struct pci_dev *dev)
{
diff --git a/include/linux/pci.h b/include/linux/pci.h
index 86c799c97b77..9b575a676888 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -856,6 +856,12 @@ struct module;
* e.g. drivers/net/e100.c.
* @sriov_configure: Optional driver callback to allow configuration of
* number of VFs to enable via sysfs "sriov_numvfs" file.
+ * @sriov_set_msix_vec_count: PF Driver callback to change number of MSI-X
+ * vectors on a VF. Triggered via sysfs "sriov_vf_msix_count".
+ * This will change MSI-X Table Size in the VF Message Control
+ * registers.
+ * @sriov_get_vf_total_msix: PF driver callback to get the total number of
+ * MSI-X vectors available for distribution to the VFs.
* @err_handler: See Documentation/PCI/pci-error-recovery.rst
* @groups: Sysfs attribute groups.
* @driver: Driver model structure.
@@ -871,6 +877,8 @@ struct pci_driver {
int (*resume)(struct pci_dev *dev); /* Device woken up */
void (*shutdown)(struct pci_dev *dev);
int (*sriov_configure)(struct pci_dev *dev, int num_vfs); /* On PF */
+ int (*sriov_set_msix_vec_count)(struct pci_dev *vf, int msix_vec_count); /* On PF */
+ u32 (*sriov_get_vf_total_msix)(struct pci_dev *pf);
const struct pci_error_handlers *err_handler;
const struct attribute_group **groups;
struct device_driver driver;
--
2.29.2