6.15-stable review patch. If anyone has any objections, please let me know.
------------------
From: Alex Williamson alex.williamson@redhat.com
[ Upstream commit e908f58b6beb337cbe4481d52c3f5c78167b1aab ]
In the below noted Fixes commit we introduced a reflck mutex to allow better scaling between devices for open and close. The reflck was based on the hot reset granularity, device level for root bus devices which cannot support hot reset or bus/slot reset otherwise. Overlooked in this were SR-IOV VFs, where there's also no bus reset option, but the default for a non-root-bus, non-slot-based device is bus level reflck granularity.
The reflck mutex has since become the dev_set mutex (via commit 2cd8b14aaa66 ("vfio/pci: Move to the device set infrastructure")) and is our defacto serialization for various operations and ioctls. It still seems to be the case though that sets of vfio-pci devices really only need serialization relative to hot resets affecting the entire set, which is not relevant to SR-IOV VFs. As described in the Closes link below, this serialization contributes to startup latency when multiple VFs sharing the same "bus" are opened concurrently.
Mark the device itself as the basis of the dev_set for SR-IOV VFs.
Reported-by: Aaron Lewis aaronlewis@google.com Closes: https://lore.kernel.org/all/20250626180424.632628-1-aaronlewis@google.com Tested-by: Aaron Lewis aaronlewis@google.com Fixes: e309df5b0c9e ("vfio/pci: Parallelize device open and release") Reviewed-by: Yi Liu yi.l.liu@intel.com Reviewed-by: Kevin Tian kevin.tian@intel.com Reviewed-by: Jason Gunthorpe jgg@nvidia.com Link: https://lore.kernel.org/r/20250626225623.1180952-1-alex.williamson@redhat.co... Signed-off-by: Alex Williamson alex.williamson@redhat.com Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/vfio/pci/vfio_pci_core.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c index 6328c3a05bcd..261a6dc5a5fc 100644 --- a/drivers/vfio/pci/vfio_pci_core.c +++ b/drivers/vfio/pci/vfio_pci_core.c @@ -2149,7 +2149,7 @@ int vfio_pci_core_register_device(struct vfio_pci_core_device *vdev) return -EBUSY; }
- if (pci_is_root_bus(pdev->bus)) { + if (pci_is_root_bus(pdev->bus) || pdev->is_virtfn) { ret = vfio_assign_device_set(&vdev->vdev, vdev); } else if (!pci_probe_reset_slot(pdev->slot)) { ret = vfio_assign_device_set(&vdev->vdev, pdev->slot);