For now the switch of vfio dirty page tracking is integrated into
@vfio_save_handler. The reason is that some PCI vendor driver may
start to track dirty base on _SAVING state of device, so if dirty
tracking is started before setting device state, vfio will report
full-dirty to QEMU.
However, the dirty bmap of all ramblocks are fully set when setup
ram saving, so it's not matter whether the device is in _SAVING
state when start vfio dirty tracking.
Moreover, this logic causes some problems [1]. The object of dirty
tracking is guest memory, but the object of @vfio_save_handler is
device state, which produces unnecessary coupling and conflicts:
1. Coupling: Their saving granule is different (perVM vs perDevice).
vfio will enable dirty_page_tracking for each devices, actually
once is enough.
2. Conflicts: The ram_save_setup() traverses all memory_listeners
to execute their log_start() and log_sync() hooks to get the
first round dirty bitmap, which is used by the bulk stage of
ram saving. However, as vfio dirty tracking is not yet started,
it can't get dirty bitmap from vfio. Then we give up the chance
to handle vfio dirty page at bulk stage.
Move the switch of vfio dirty_page_tracking into vfio_memory_listener
can solve above problems. Besides, Do not require devices in SAVING
state for vfio_sync_dirty_bitmap().
[1] https://www.spinics.net/lists/kvm/msg229967.html
Reported-by: Zenghui Yu <yuzenghui@huawei.com>
Signed-off-by: Keqian Zhu <zhukeqian1@huawei.com>
Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20210309031913.11508-1-zhukeqian1@huawei.com>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
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