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Coverage Report for CI Build 37281200351Coverage increased (+0.05%) to 39.089%Details
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Coverage RegressionsNo coverage regressions found. Coverage Stats
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Virtio workers used to hold RamBus::lock_layout() for as long as a device was running, so any runtime change of the guest RAM layout, e.g. memory hot-plug, blocked forever on the write lock. Borrowing the read-copy-update idea from Linux RCU, - Readers call RamBus::load() to get an immutable snapshot. The read lock is only held while cloning the Arc. - Writers call RamBus::update(), which copies the layout, applies the change and publishes the result atomically. A failed update publishes nothing, and Memory batches all RAM ranges of a region into a single update. - Each published layout carries a generation number, so a reader can detect a stale snapshot with a single atomic load by comparing Ram::generation() with RamBus::generation(). Since ArcMemPages is reference counted, a snapshot keeps every host mapping it refers to alive, even after the slot is removed from the bus. This commit fixes the deadlock, but a running virtio worker still uses the snapshot taken when the device was activated. Follow-up commits make workers pick up new snapshots. Assisted-by: Antigravity:Claude-Fable-5.1 Signed-off-by: Changyuan Lyu <changyuanl@google.com>
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