vgsp: xw-mirror page-reuse guards + submit-status clearer scaffold (SESSION 148 r873)

The unguarded 3 ms mirror loop kept writing the count law into its latched
page after the guest had reused it (r872 evidence: guest 'Bad page map ...
pmd:102656067' pointing at exactly the mirrored page's PA as another
process's PTE table). The loop now latches the progress word's base bits and
stops permanently when they change or are zeroed, and re-checks the counter
object's signature every 64th tick. New sema_xw_comp parameter + vgsp-xwcomp
kthread can clear a submit member's armed 0x8000 status (value 0 pattern
only); r874 proved an unverified clear into a false member kills Xorg within
seconds, so it stays uninjected until the member address is watched live.

0 files changed, 0 insertions, 0 deletions