Register copied the protection it had recorded for pages it already
watched over the protection the kernel had just reported. A guest that
reserves address space, which registers it as PROT_NONE, then maps
direct memory over it read-write and registers it again kept the stale
PROT_NONE. Collect only write-protects pages with PROT_WRITE, so writes
to that memory were reported once and never again. With PPSA12544 on
the macOS port, the title menu text blinked and glyphs went missing.
Register now keeps a recorded protection only where its own write
protection explains what the kernel reports, and takes the kernel's
protection otherwise. A protected page that was mapped again also loses
its protected mark, so erase no longer restores the old protection over
the new mapping. The kernel is read under the lock, so a concurrent
Collect cannot protect a page between the read and the merge.
Test write_watch_mapped: a reservation, a mapping over it and a second
registration keep reporting writes, and a protected page reserved again
stays PROT_NONE.
AI-assisted: yes
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