vfio/pci-core: Add capability for AtomicOp completer support

Test and enable PCIe AtomicOp completer support of various widths and
report via device-info capability to userspace.

Reviewed-by: Cédric Le Goater <clg@redhat.com>
Reviewed-by: Robin Voetter <robin@streamhpc.com>
Tested-by: Robin Voetter <robin@streamhpc.com>
Link: https://lore.kernel.org/r/20230519214748.402003-1-alex.williamson@redhat.com
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

Author: awilliam

drivers/vfio/pci/vfio_pci_core.c

@@ -885,6 +885,37 @@ int vfio_pci_core_register_dev_region(struct vfio_pci_core_device *vdev,
 }
 EXPORT_SYMBOL_GPL(vfio_pci_core_register_dev_region);
 
+static int vfio_pci_info_atomic_cap(struct vfio_pci_core_device *vdev,
+				    struct vfio_info_cap *caps)
+{
+	struct vfio_device_info_cap_pci_atomic_comp cap = {
+		.header.id = VFIO_DEVICE_INFO_CAP_PCI_ATOMIC_COMP,
+		.header.version = 1
+	};
+	struct pci_dev *pdev = pci_physfn(vdev->pdev);
+	u32 devcap2;
+
+	pcie_capability_read_dword(pdev, PCI_EXP_DEVCAP2, &devcap2);
+
+	if ((devcap2 & PCI_EXP_DEVCAP2_ATOMIC_COMP32) &&
+	    !pci_enable_atomic_ops_to_root(pdev, PCI_EXP_DEVCAP2_ATOMIC_COMP32))
+		cap.flags |= VFIO_PCI_ATOMIC_COMP32;
+
+	if ((devcap2 & PCI_EXP_DEVCAP2_ATOMIC_COMP64) &&
+	    !pci_enable_atomic_ops_to_root(pdev, PCI_EXP_DEVCAP2_ATOMIC_COMP64))
+		cap.flags |= VFIO_PCI_ATOMIC_COMP64;
+
+	if ((devcap2 & PCI_EXP_DEVCAP2_ATOMIC_COMP128) &&
+	    !pci_enable_atomic_ops_to_root(pdev,
+					   PCI_EXP_DEVCAP2_ATOMIC_COMP128))
+		cap.flags |= VFIO_PCI_ATOMIC_COMP128;
+
+	if (!cap.flags)
+		return -ENODEV;
+
+	return vfio_info_add_capability(caps, &cap.header, sizeof(cap));
+}
+
 static int vfio_pci_ioctl_get_info(struct vfio_pci_core_device *vdev,
 				   struct vfio_device_info __user *arg)
 {
@@ -923,6 +954,13 @@ static int vfio_pci_ioctl_get_info(struct vfio_pci_core_device *vdev,
 		return ret;
 	}
 
+	ret = vfio_pci_info_atomic_cap(vdev, &caps);
+	if (ret && ret != -ENODEV) {
+		pci_warn(vdev->pdev,
+			 "Failed to setup AtomicOps info capability\n");
+		return ret;
+	}
+
 	if (caps.size) {
 		info.flags |= VFIO_DEVICE_FLAGS_CAPS;
 		if (info.argsz < sizeof(info) + caps.size) {

include/uapi/linux/vfio.h

@@ -240,6 +240,20 @@ struct vfio_device_info {
 #define VFIO_DEVICE_INFO_CAP_ZPCI_UTIL		3
 #define VFIO_DEVICE_INFO_CAP_ZPCI_PFIP		4
 
+/*
+ * The following VFIO_DEVICE_INFO capability reports support for PCIe AtomicOp
+ * completion to the root bus with supported widths provided via flags.
+ */
+#define VFIO_DEVICE_INFO_CAP_PCI_ATOMIC_COMP	5
+struct vfio_device_info_cap_pci_atomic_comp {
+	struct vfio_info_cap_header header;
+	__u32 flags;
+#define VFIO_PCI_ATOMIC_COMP32	(1 << 0)
+#define VFIO_PCI_ATOMIC_COMP64	(1 << 1)
+#define VFIO_PCI_ATOMIC_COMP128	(1 << 2)
+	__u32 reserved;
+};
+
 /**
  * VFIO_DEVICE_GET_REGION_INFO - _IOWR(VFIO_TYPE, VFIO_BASE + 8,
  *				       struct vfio_region_info)