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

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".

Link: https://lore.kernel.org/linux-pci/20210314124256.70253-2-leon@kernel.org
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>

diff --git a/Documentation/ABI/testing/sysfs-bus-pci b/Documentation/ABI/testing/sysfs-bus-pci
index 25c9c39..e5cfd17 100644 (file)
--- 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 physical function (PF).
+               It contains the total number of MSI-X vectors available for
+               assignment to all virtual functions (VFs) associated with PF.
+               The value will be 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 virtual function (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 4afd4ee..afc06e6 100644 (file)
--- 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 @@ failed:
        return rc;
 }
 
+#ifdef CONFIG_PCI_MSI
+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);
+
+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);
+#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 f8afd54..a6b8fbb 100644 (file)
--- 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 ef7c466..afb87b9 100644 (file)
--- 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 86c799c..9b575a6 100644 (file)
--- 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;