[RFC PATCH v2 16/16] vfio/pci: Enable host PCI error recovery for vfio-pci

[Shameer Kolothum <skolothumtho@nvidia.com>]

Enable recovery support for generic vfio-pci. Userspace opts in through
VFIO_DEVICE_FEATURE_PCI_ERROR_RECOVERY. Open rejects an active host
recovery even without opt-in. Leave variant drivers disabled until their
access paths are covered.

Exclude CXL memory devices and s390: Restricted CXL Host (RCH) and s390
mediated recovery can omit completion callbacks. On s390, permanent-failure
notification also blocks config access, so draining SRCU can deadlock
with config readers.

Assisted-by: LLM
Signed-off-by: Shameer Kolothum <skolothumtho@nvidia.com>
---
 drivers/vfio/pci/vfio_pci.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
index 4887dd062c77..043371c2882c 100644
--- a/drivers/vfio/pci/vfio_pci.c
+++ b/drivers/vfio/pci/vfio_pci.c
@@ -129,6 +129,7 @@ static int vfio_pci_init_dev(struct vfio_device *core_vdev)
 {
 	struct vfio_pci_core_device *vdev =
 		container_of(core_vdev, struct vfio_pci_core_device, vdev);
+	struct pci_dev *pdev = to_pci_dev(core_vdev->dev);
 
 	/*
 	 * These behaviors originated in vfio-pci and moved into
@@ -139,6 +140,14 @@ static int vfio_pci_init_dev(struct vfio_device *core_vdev)
 	 */
 	vdev->nointxmask = nointxmask;
 	vdev->disable_idle_d3 = disable_idle_d3;
+	/*
+	 * CXL RCH and s390 mediated recovery can omit completion callbacks.
+	 * s390 also blocks config access across failure notification, which
+	 * prevents draining SRCU readers waiting for config access.
+	 */
+	if (!IS_ENABLED(CONFIG_S390) &&
+	    (pdev->class >> 8) != PCI_CLASS_MEMORY_CXL)
+		vdev->pci_recovery_supported = true;
 #ifdef CONFIG_VFIO_PCI_VGA
 	vdev->disable_vga = disable_vga;
 #endif
-- 
2.43.0