vfio/virtio: Enable live migration once VIRTIO_PCI was configured

Now that the driver supports live migration, only the legacy IO
functionality depends on config VIRTIO_PCI_ADMIN_LEGACY.

As part of that we introduce a bool configuration option as a sub menu
under the driver's main live migration feature named
VIRTIO_VFIO_PCI_ADMIN_LEGACY, to control the legacy IO functionality.

This will let users configuring the kernel, know which features from the
description might be available in the resulting driver.

As of that, move the legacy IO into a separate file to be compiled only
once CONFIG_VIRTIO_VFIO_PCI_ADMIN_LEGACY was configured and let the live
migration depends only on VIRTIO_PCI.

Signed-off-by: Yishai Hadas <yishaih@nvidia.com>
Link: https://lore.kernel.org/r/20241113115200.209269-8-yishaih@nvidia.com
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

Author: Yishai Hadas

drivers/vfio/pci/virtio/Kconfig

@@ -1,15 +1,31 @@
 # SPDX-License-Identifier: GPL-2.0-only
 config VIRTIO_VFIO_PCI
-        tristate "VFIO support for VIRTIO NET PCI devices"
-        depends on VIRTIO_PCI && VIRTIO_PCI_ADMIN_LEGACY
-        select VFIO_PCI_CORE
-        help
-          This provides support for exposing VIRTIO NET VF devices which support
-          legacy IO access, using the VFIO framework that can work with a legacy
-          virtio driver in the guest.
-          Based on PCIe spec, VFs do not support I/O Space.
-          As of that this driver emulates I/O BAR in software to let a VF be
-          seen as a transitional device by its users and let it work with
-          a legacy driver.
-
-          If you don't know what to do here, say N.
+	tristate "VFIO support for VIRTIO NET PCI VF devices"
+	depends on VIRTIO_PCI
+	select VFIO_PCI_CORE
+	help
+	  This provides migration support for VIRTIO NET PCI VF devices
+	  using the VFIO framework. Migration support requires the
+	  SR-IOV PF device to support specific VIRTIO extensions,
+	  otherwise this driver provides no additional functionality
+	  beyond vfio-pci.
+
+	  Migration support in this driver relies on dirty page tracking
+	  provided by the IOMMU hardware and exposed through IOMMUFD, any
+	  other use cases are dis-recommended.
+
+	  If you don't know what to do here, say N.
+
+config VIRTIO_VFIO_PCI_ADMIN_LEGACY
+	bool "Legacy I/O support for VIRTIO NET PCI VF devices"
+	depends on VIRTIO_VFIO_PCI && VIRTIO_PCI_ADMIN_LEGACY
+	default y
+	help
+	  This extends the virtio-vfio-pci driver to support legacy I/O
+	  access, allowing use of legacy virtio drivers with VIRTIO NET
+	  PCI VF devices. Legacy I/O support requires the SR-IOV PF
+	  device to support and enable specific VIRTIO extensions,
+	  otherwise this driver provides no additional functionality
+	  beyond vfio-pci.
+
+	  If you don't know what to do here, say N.

drivers/vfio/pci/virtio/Makefile

@@ -1,3 +1,4 @@
 # SPDX-License-Identifier: GPL-2.0-only
 obj-$(CONFIG_VIRTIO_VFIO_PCI) += virtio-vfio-pci.o
 virtio-vfio-pci-y := main.o migrate.o
+virtio-vfio-pci-$(CONFIG_VIRTIO_VFIO_PCI_ADMIN_LEGACY) += legacy_io.o

drivers/vfio/pci/virtio/common.h

@@ -78,6 +78,7 @@ struct virtiovf_migration_file {
 
 struct virtiovf_pci_core_device {
 	struct vfio_pci_core_device core_device;
+#ifdef CONFIG_VIRTIO_VFIO_PCI_ADMIN_LEGACY
 	u8 *bar0_virtual_buf;
 	/* synchronize access to the virtual buf */
 	struct mutex bar_mutex;
@@ -87,6 +88,7 @@ struct virtiovf_pci_core_device {
 	__le16 pci_cmd;
 	u8 bar0_virtual_buf_size;
 	u8 notify_bar;
+#endif
 
 	/* LM related */
 	u8 migrate_cap:1;
@@ -105,4 +107,21 @@ void virtiovf_open_migration(struct virtiovf_pci_core_device *virtvdev);
 void virtiovf_close_migration(struct virtiovf_pci_core_device *virtvdev);
 void virtiovf_migration_reset_done(struct pci_dev *pdev);
 
+#ifdef CONFIG_VIRTIO_VFIO_PCI_ADMIN_LEGACY
+int virtiovf_open_legacy_io(struct virtiovf_pci_core_device *virtvdev);
+long virtiovf_vfio_pci_core_ioctl(struct vfio_device *core_vdev,
+				  unsigned int cmd, unsigned long arg);
+int virtiovf_pci_ioctl_get_region_info(struct vfio_device *core_vdev,
+				       unsigned int cmd, unsigned long arg);
+ssize_t virtiovf_pci_core_write(struct vfio_device *core_vdev,
+				const char __user *buf, size_t count,
+				loff_t *ppos);
+ssize_t virtiovf_pci_core_read(struct vfio_device *core_vdev, char __user *buf,
+			       size_t count, loff_t *ppos);
+bool virtiovf_support_legacy_io(struct pci_dev *pdev);
+int virtiovf_init_legacy_io(struct virtiovf_pci_core_device *virtvdev);
+void virtiovf_release_legacy_io(struct virtiovf_pci_core_device *virtvdev);
+void virtiovf_legacy_io_reset_done(struct pci_dev *pdev);
+#endif
+
 #endif /* VIRTIO_VFIO_COMMON_H */