vfio/pci: Enable AtomicOps completers on root ports

Dynamically enable Atomic Ops completer support around realize/exit of
vfio-pci devices reporting host support for these accesses and adhering
to a minimal configuration standard.  While the Atomic Ops completer
bits in the root port device capabilities2 register are read-only, the
PCIe spec does allow RO bits to change to reflect hardware state.  We
take advantage of that here around the realize and exit functions of
the vfio-pci device.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Robin Voetter <robin@streamhpc.com>
Tested-by: Robin Voetter <robin@streamhpc.com>
Signed-off-by: Cédric Le Goater <clg@redhat.com>

hw/vfio/pci.c

@@ -1828,6 +1828,81 @@ static void vfio_add_emulated_long(VFIOPCIDevice *vdev, int pos,
     vfio_set_long_bits(vdev->emulated_config_bits + pos, mask, mask);
 }
 
+static void vfio_pci_enable_rp_atomics(VFIOPCIDevice *vdev)
+{
+    struct vfio_device_info_cap_pci_atomic_comp *cap;
+    g_autofree struct vfio_device_info *info = NULL;
+    PCIBus *bus = pci_get_bus(&vdev->pdev);
+    PCIDevice *parent = bus->parent_dev;
+    struct vfio_info_cap_header *hdr;
+    uint32_t mask = 0;
+    uint8_t *pos;
+
+    /*
+     * PCIe Atomic Ops completer support is only added automatically for single
+     * function devices downstream of a root port supporting DEVCAP2.  Support
+     * is added during realize and, if added, removed during device exit.  The
+     * single function requirement avoids conflicting requirements should a
+     * slot be composed of multiple devices with differing capabilities.
+     */
+    if (pci_bus_is_root(bus) || !parent || !parent->exp.exp_cap ||
+        pcie_cap_get_type(parent) != PCI_EXP_TYPE_ROOT_PORT ||
+        pcie_cap_get_version(parent) != PCI_EXP_FLAGS_VER2 ||
+        vdev->pdev.devfn ||
+        vdev->pdev.cap_present & QEMU_PCI_CAP_MULTIFUNCTION) {
+        return;
+    }
+
+    pos = parent->config + parent->exp.exp_cap + PCI_EXP_DEVCAP2;
+
+    /* Abort if there'a already an Atomic Ops configuration on the root port */
+    if (pci_get_long(pos) & (PCI_EXP_DEVCAP2_ATOMIC_COMP32 |
+                             PCI_EXP_DEVCAP2_ATOMIC_COMP64 |
+                             PCI_EXP_DEVCAP2_ATOMIC_COMP128)) {
+        return;
+    }
+
+    info = vfio_get_device_info(vdev->vbasedev.fd);
+    if (!info) {
+        return;
+    }
+
+    hdr = vfio_get_device_info_cap(info, VFIO_DEVICE_INFO_CAP_PCI_ATOMIC_COMP);
+    if (!hdr) {
+        return;
+    }
+
+    cap = (void *)hdr;
+    if (cap->flags & VFIO_PCI_ATOMIC_COMP32) {
+        mask |= PCI_EXP_DEVCAP2_ATOMIC_COMP32;
+    }
+    if (cap->flags & VFIO_PCI_ATOMIC_COMP64) {
+        mask |= PCI_EXP_DEVCAP2_ATOMIC_COMP64;
+    }
+    if (cap->flags & VFIO_PCI_ATOMIC_COMP128) {
+        mask |= PCI_EXP_DEVCAP2_ATOMIC_COMP128;
+    }
+
+    if (!mask) {
+        return;
+    }
+
+    pci_long_test_and_set_mask(pos, mask);
+    vdev->clear_parent_atomics_on_exit = true;
+}
+
+static void vfio_pci_disable_rp_atomics(VFIOPCIDevice *vdev)
+{
+    if (vdev->clear_parent_atomics_on_exit) {
+        PCIDevice *parent = pci_get_bus(&vdev->pdev)->parent_dev;
+        uint8_t *pos = parent->config + parent->exp.exp_cap + PCI_EXP_DEVCAP2;
+
+        pci_long_test_and_clear_mask(pos, PCI_EXP_DEVCAP2_ATOMIC_COMP32 |
+                                          PCI_EXP_DEVCAP2_ATOMIC_COMP64 |
+                                          PCI_EXP_DEVCAP2_ATOMIC_COMP128);
+    }
+}
+
 static int vfio_setup_pcie_cap(VFIOPCIDevice *vdev, int pos, uint8_t size,
                                Error **errp)
 {
@@ -1931,6 +2006,8 @@ static int vfio_setup_pcie_cap(VFIOPCIDevice *vdev, int pos, uint8_t size,
                            QEMU_PCI_EXP_LNKCAP_MLS(QEMU_PCI_EXP_LNK_2_5GT), ~0);
             vfio_add_emulated_word(vdev, pos + PCI_EXP_LNKCTL, 0, ~0);
         }
+
+        vfio_pci_enable_rp_atomics(vdev);
     }
 
     /*
@@ -3273,6 +3350,7 @@ static void vfio_exitfn(PCIDevice *pdev)
         timer_free(vdev->intx.mmap_timer);
     }
     vfio_teardown_msi(vdev);
+    vfio_pci_disable_rp_atomics(vdev);
     vfio_bars_exit(vdev);
     vfio_migration_exit(&vdev->vbasedev);
 }

hw/vfio/pci.h

@@ -174,6 +174,7 @@ struct VFIOPCIDevice {
     bool no_vfio_ioeventfd;
     bool enable_ramfb;
     bool defer_kvm_irq_routing;
+    bool clear_parent_atomics_on_exit;
     VFIODisplay *dpy;
     Notifier irqchip_change_notifier;
 };