Merge tag 'vfio-updates-20230307.1' of https://gitlab.com/alex.williamson/qemu into staging

VFIO updates for 8.0

 * Device level dirty page tracking support for vfio migration, as well as
   various cleanups and consolidations. (Avihai Horon, Joao Martins)

 * Trivial cleanup of migration entry points. (Alex Williamson)

 * Fix trace event typo. (Cédric Le Goater)

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# gpg:                using RSA key 42F6C04E540BD1A99E7B8A90239B9B6E3BB08B22
# gpg:                issuer "alex.williamson@redhat.com"
# gpg: Good signature from "Alex Williamson <alex.williamson@redhat.com>" [full]
# gpg:                 aka "Alex Williamson <alex@shazbot.org>" [full]
# gpg:                 aka "Alex Williamson <alwillia@redhat.com>" [full]
# gpg:                 aka "Alex Williamson <alex.l.williamson@gmail.com>" [full]
# Primary key fingerprint: 42F6 C04E 540B D1A9 9E7B  8A90 239B 9B6E 3BB0 8B22

* tag 'vfio-updates-20230307.1' of https://gitlab.com/alex.williamson/qemu:
  vfio: Fix vfio_get_dev_region() trace event
  vfio/migration: Rename entry points
  docs/devel: Document VFIO device dirty page tracking
  vfio/migration: Query device dirty page tracking support
  vfio/migration: Block migration with vIOMMU
  vfio/common: Add device dirty page bitmap sync
  vfio/common: Extract code from vfio_get_dirty_bitmap() to new function
  vfio/common: Add device dirty page tracking start/stop
  vfio/common: Record DMA mapped IOVA ranges
  vfio/common: Add helper to consolidate iova/end calculation
  vfio/common: Consolidate skip/invalid section into helper
  vfio/common: Use a single tracepoint for skipped sections
  vfio/common: Add helper to validate iova/end against hostwin
  vfio/common: Add VFIOBitmap and alloc function
  vfio/common: Abort migration if dirty log start/stop/sync fails
  vfio/common: Fix wrong %m usages
  vfio/common: Fix error reporting in vfio_get_dirty_bitmap()

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

1 files changed, 31 insertions, 15 deletions

diff --git a/docs/devel/vfio-migration.rst b/docs/devel/vfio-migration.rst
index c214c73..1b68ccf 100644
--- a/docs/devel/vfio-migration.rst
+++ b/docs/devel/vfio-migration.rst
@@ -59,22 +59,37 @@ System memory dirty pages tracking
 ----------------------------------
 
 A ``log_global_start`` and ``log_global_stop`` memory listener callback informs
-the VFIO IOMMU module to start and stop dirty page tracking. A ``log_sync``
-memory listener callback marks those system memory pages as dirty which are
-used for DMA by the VFIO device. The dirty pages bitmap is queried per
-container. All pages pinned by the vendor driver through external APIs have to
-be marked as dirty during migration. When there are CPU writes, CPU dirty page
-tracking can identify dirtied pages, but any page pinned by the vendor driver
-can also be written by the device. There is currently no device or IOMMU
-support for dirty page tracking in hardware.
+the VFIO dirty tracking module to start and stop dirty page tracking. A
+``log_sync`` memory listener callback queries the dirty page bitmap from the
+dirty tracking module and marks system memory pages which were DMA-ed by the
+VFIO device as dirty. The dirty page bitmap is queried per container.
+
+Currently there are two ways dirty page tracking can be done:
+(1) Device dirty tracking:
+In this method the device is responsible to log and report its DMAs. This
+method can be used only if the device is capable of tracking its DMAs.
+Discovering device capability, starting and stopping dirty tracking, and
+syncing the dirty bitmaps from the device are done using the DMA logging uAPI.
+More info about the uAPI can be found in the comments of the
+``vfio_device_feature_dma_logging_control`` and
+``vfio_device_feature_dma_logging_report`` structures in the header file
+linux-headers/linux/vfio.h.
+
+(2) VFIO IOMMU module:
+In this method dirty tracking is done by IOMMU. However, there is currently no
+IOMMU support for dirty page tracking. For this reason, all pages are
+perpetually marked dirty, unless the device driver pins pages through external
+APIs in which case only those pinned pages are perpetually marked dirty.
+
+If the above two methods are not supported, all pages are perpetually marked
+dirty by QEMU.
 
 By default, dirty pages are tracked during pre-copy as well as stop-and-copy
-phase. So, a page pinned by the vendor driver will be copied to the destination
-in both phases. Copying dirty pages in pre-copy phase helps QEMU to predict if
-it can achieve its downtime tolerances. If QEMU during pre-copy phase keeps
-finding dirty pages continuously, then it understands that even in stop-and-copy
-phase, it is likely to find dirty pages and can predict the downtime
-accordingly.
+phase. So, a page marked as dirty will be copied to the destination in both
+phases. Copying dirty pages in pre-copy phase helps QEMU to predict if it can
+achieve its downtime tolerances. If QEMU during pre-copy phase keeps finding
+dirty pages continuously, then it understands that even in stop-and-copy phase,
+it is likely to find dirty pages and can predict the downtime accordingly.
 
 QEMU also provides a per device opt-out option ``pre-copy-dirty-page-tracking``
 which disables querying the dirty bitmap during pre-copy phase. If it is set to
@@ -89,7 +104,8 @@ phase of migration. In that case, the unmap ioctl returns any dirty pages in
 that range and QEMU reports corresponding guest physical pages dirty. During
 stop-and-copy phase, an IOMMU notifier is used to get a callback for mapped
 pages and then dirty pages bitmap is fetched from VFIO IOMMU modules for those
-mapped ranges.
+mapped ranges. If device dirty tracking is enabled with vIOMMU, live migration
+will be blocked.
 
 Flow of state changes during Live migration
 ===========================================