Importing guest memory collected the write watch over the whole import,
which write-protected every page of it, so pages nothing had collected yet
took a write fault on their first CPU write. The import now collects only
the parts a collect already protects (GuestWriteWatchCollectArmed). The
rest stays unprotected until something collects it, which reports it as
written; a GPU write recorded into such memory (MarkWritten) first collects
the never-collected parts of its 64 KiB blocks
(GuestWriteWatchCollectFresh), so that report is older than the GPU's
results and does not read as a CPU write over them.
Those pages are stamped as written and their CPU pages are noted, but the
block's CPU stamp is left alone, so a GPU label record or a pending storage
image elsewhere in the block does not see a CPU write. StoredOver and
UnchangedSinceCollected read the noted pages whenever a block has them, so
a store to such a page is still seen by a check over that page. The extra
generation step happens only when something was collected; a block whose
write protection fails is unwatched and the write returns no generation.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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