[RFC PATCH 3/9] vfio/pci: register a default migration region

[Yan Zhao <yan.y.zhao@intel.com>]

Vendor driver specifies when to support a migration region through cap
VFIO_PCI_DEVICE_CAP_MIGRATION in vfio_pci_mediate_ops->open().

If vfio-pci detects this cap, it creates a default migration region on
behalf of vendor driver with region len=0 and region->ops=null.
Vendor driver should override this region's len, flags, rw, mmap in
its vfio_pci_mediate_ops.

This migration region definition is aligned to QEMU vfio migration code v8:
(https://lists.gnu.org/archive/html/qemu-devel/2019-08/msg05542.html)

Cc: Kevin Tian <kevin.tian@intel.com>

Signed-off-by: Yan Zhao <yan.y.zhao@intel.com>
---
 drivers/vfio/pci/vfio_pci.c |  15 ++++
 include/linux/vfio.h        |   1 +
 include/uapi/linux/vfio.h   | 149 ++++++++++++++++++++++++++++++++++++
 3 files changed, 165 insertions(+)

diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
index f3730252ee82..059660328be2 100644
--- a/drivers/vfio/pci/vfio_pci.c
+++ b/drivers/vfio/pci/vfio_pci.c
@@ -115,6 +115,18 @@ static inline bool vfio_pci_is_vga(struct pci_dev *pdev)
 	return (pdev->class >> 8) == PCI_CLASS_DISPLAY_VGA;
 }
 
+/**
+ * init a region to hold migration ctl & data
+ */
+void init_migration_region(struct vfio_pci_device *vdev)
+{
+	vfio_pci_register_dev_region(vdev, VFIO_REGION_TYPE_MIGRATION,
+		VFIO_REGION_SUBTYPE_MIGRATION,
+		NULL, 0,
+		VFIO_REGION_INFO_FLAG_READ | VFIO_REGION_INFO_FLAG_WRITE,
+		NULL);
+}
+
 static void vfio_pci_probe_mmaps(struct vfio_pci_device *vdev)
 {
 	struct resource *res;
@@ -523,6 +535,9 @@ static int vfio_pci_open(void *device_data)
 				vdev->mediate_ops = mentry->ops;
 				vdev->mediate_handle = handle;
 
+				if (caps & VFIO_PCI_DEVICE_CAP_MIGRATION)
+					init_migration_region(vdev);
+
 				pr_info("vfio pci found mediate_ops %s, caps=%llx, handle=%x for %x:%x\n",
 						vdev->mediate_ops->name, caps,
 						handle, vdev->pdev->vendor,
diff --git a/include/linux/vfio.h b/include/linux/vfio.h
index 0265e779acd1..cddea8e9dcb2 100644
--- a/include/linux/vfio.h
+++ b/include/linux/vfio.h
@@ -197,6 +197,7 @@ extern void vfio_virqfd_disable(struct virqfd **pvirqfd);
 
 struct vfio_pci_mediate_ops {
 	char	*name;
+#define VFIO_PCI_DEVICE_CAP_MIGRATION (0x01)
 	int	(*open)(struct pci_dev *pdev, u64 *caps, u32 *handle);
 	void	(*release)(int handle);
 	void	(*get_region_info)(int handle,
diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
index 9e843a147ead..caf8845a67a6 100644
--- a/include/uapi/linux/vfio.h
+++ b/include/uapi/linux/vfio.h
@@ -306,6 +306,155 @@ struct vfio_region_info_cap_type {
 #define VFIO_REGION_TYPE_GFX                    (1)
 #define VFIO_REGION_TYPE_CCW			(2)
 
+/* Migration region type and sub-type */
+#define VFIO_REGION_TYPE_MIGRATION          (3)
+#define VFIO_REGION_SUBTYPE_MIGRATION           (1)
+
+/**
+ * Structure vfio_device_migration_info is placed at 0th offset of
+ * VFIO_REGION_SUBTYPE_MIGRATION region to get/set VFIO device related migration
+ * information. Field accesses from this structure are only supported at their
+ * native width and alignment, otherwise the result is undefined and vendor
+ * drivers should return an error.
+ *
+ * device_state: (read/write)
+ *      To indicate vendor driver the state VFIO device should be transitioned
+ *      to. If device state transition fails, write on this field return error.
+ *      It consists of 3 bits:
+ *      - If bit 0 set, indicates _RUNNING state. When its reset, that indicates
+ *        _STOPPED state. When device is changed to _STOPPED, driver should stop
+ *        device before write() returns.
+ *      - If bit 1 set, indicates _SAVING state.
+ *      - If bit 2 set, indicates _RESUMING state.
+ *      Bits 3 - 31 are reserved for future use. User should perform
+ *      read-modify-write operation on this field.
+ *      _SAVING and _RESUMING bits set at the same time is invalid state.
+ *
+ * pending bytes: (read only)
+ *      Number of pending bytes yet to be migrated from vendor driver
+ *
+ * data_offset: (read only)
+ *      User application should read data_offset in migration region from where
+ *      user application should read device data during _SAVING state or write
+ *      device data during _RESUMING state or read dirty pages bitmap. See below
+ *      for detail of sequence to be followed.
+ *
+ * data_size: (read/write)
+ *      User application should read data_size to get size of data copied in
+ *      migration region during _SAVING state and write size of data copied in
+ *      migration region during _RESUMING state.
+ *
+ * start_pfn: (write only)
+ *      Start address pfn to get bitmap of dirty pages from vendor driver duing
+ *      _SAVING state.
+ *
+ * page_size: (write only)
+ *      User application should write the page_size of pfn.
+ *
+ * total_pfns: (write only)
+ *      Total pfn count from start_pfn for which dirty bitmap is requested.
+ *
+ * copied_pfns: (read only)
+ *      pfn count for which dirty bitmap is copied to migration region.
+ *      Vendor driver should copy the bitmap with bits set only for pages to be
+ *      marked dirty in migration region.
+ *      - Vendor driver should return VFIO_DEVICE_DIRTY_PFNS_NONE if none of the
+ *        pages are dirty in requested range or rest of the range.
+ *      - Vendor driver should return VFIO_DEVICE_DIRTY_PFNS_ALL to mark all
+ *        pages dirty in the given range or rest of the range.
+ *      - Vendor driver should return pfn count for which bitmap is written in
+ *        the region.
+ *
+ * Migration region looks like:
+ *  ------------------------------------------------------------------
+ * |vfio_device_migration_info|    data section                      |
+ * |                          |     ///////////////////////////////  |
+ * ------------------------------------------------------------------
+ *   ^                              ^                             ^
+ *  offset 0-trapped part        data_offset                 data_size
+ *
+ * Data section is always followed by vfio_device_migration_info structure
+ * in the region, so data_offset will always be non-0. Offset from where data
+ * is copied is decided by kernel driver, data section can be trapped or
+ * mapped or partitioned, depending on how kernel driver defines data section.
+ * Data section partition can be defined as mapped by sparse mmap capability.
+ * If mmapped, then data_offset should be page aligned, where as initial section
+ * which contain vfio_device_migration_info structure might not end at offset
+ * which is page aligned.
+ * Data_offset can be same or different for device data and dirty pages bitmap.
+ * Vendor driver should decide whether to partition data section and how to
+ * partition the data section. Vendor driver should return data_offset
+ * accordingly.
+ *
+ * Sequence to be followed for _SAVING|_RUNNING device state or pre-copy phase
+ * and for _SAVING device state or stop-and-copy phase:
+ * a. read pending_bytes. If pending_bytes > 0, go through below steps.
+ * b. read data_offset, indicates kernel driver to write data to staging buffer.
+ * c. read data_size, amount of data in bytes written by vendor driver in
+ *    migration region.
+ * d. read data_size bytes of data from data_offset in the migration region.
+ * e. process data.
+ * f. Loop through a to e.
+ *
+ * To copy system memory content during migration, vendor driver should be able
+ * to report system memory pages which are dirtied by that driver. For such
+ * dirty page reporting, user application should query for a range of GFNs
+ * relative to device address space (IOVA), then vendor driver should provide
+ * the bitmap of pages from this range which are dirtied by him through
+ * migration region where each bit represents a page and bit set to 1 represents
+ * that the page is dirty.
+ * User space application should take care of copying content of system memory
+ * for those pages.
+ *
+ * Steps to get dirty page bitmap:
+ * a. write start_pfn, page_size and total_pfns.
+ * b. read copied_pfns. Vendor driver should take one of the below action:
+ *     - Vendor driver should return VFIO_DEVICE_DIRTY_PFNS_NONE if driver
+ *       doesn't have any page to report dirty in given range or rest of the
+ *       range. Exit the loop.
+ *     - Vendor driver should return VFIO_DEVICE_DIRTY_PFNS_ALL to mark all
+ *       pages dirty for given range or rest of the range. User space
+ *       application mark all pages in the range as dirty and exit the loop.
+ *     - Vendor driver should return copied_pfns and provide bitmap for
+ *       copied_pfn in migration region.
+ * c. read data_offset, where vendor driver has written bitmap.
+ * d. read bitmap from the migration region from data_offset.
+ * e. Iterate through steps a to d while (total copied_pfns < total_pfns)
+ *
+ * Sequence to be followed while _RESUMING device state:
+ * While data for this device is available, repeat below steps:
+ * a. read data_offset from where user application should write data.
+ * b. write data of data_size to migration region from data_offset.
+ * c. write data_size which indicates vendor driver that data is written in
+ *    staging buffer.
+ *
+ * For user application, data is opaque. User should write data in the same
+ * order as received.
+ */
+
+struct vfio_device_migration_info {
+	__u32 device_state;		/* VFIO device state */
+#define VFIO_DEVICE_STATE_RUNNING	(1 << 0)
+#define VFIO_DEVICE_STATE_SAVING	(1 << 1)
+#define VFIO_DEVICE_STATE_RESUMING	(1 << 2)
+#define VFIO_DEVICE_STATE_MASK		(VFIO_DEVICE_STATE_RUNNING | \
+					VFIO_DEVICE_STATE_SAVING | \
+					VFIO_DEVICE_STATE_RESUMING)
+#define VFIO_DEVICE_STATE_INVALID	(VFIO_DEVICE_STATE_SAVING | \
+					VFIO_DEVICE_STATE_RESUMING)
+	__u32 reserved;
+	__u64 pending_bytes;
+	__u64 data_offset;
+	__u64 data_size;
+	__u64 start_pfn;
+	__u64 page_size;
+	__u64 total_pfns;
+	__u64 copied_pfns;
+#define VFIO_DEVICE_DIRTY_PFNS_NONE	(0)
+#define VFIO_DEVICE_DIRTY_PFNS_ALL	(~0ULL)
+} __attribute__((packed));
+
+
 /* sub-types for VFIO_REGION_TYPE_PCI_* */
 
 /* 8086 vendor PCI sub-types */
-- 
2.17.1