PPCBUG-160 partial: stswi's single invalidate_for_write(ea) only covered
the first cache line; with nb up to 32, the write span can cross a 128-byte
line boundary. Replace with two-call guard:
first_line = ea & !RESERVATION_MASK
last_line = ea.wrapping_add(nb - 1) & !RESERVATION_MASK
invalidate first; if last != first, invalidate last.
PPCBUG-160 partial: stswx had the same single-call gap; nb from XER[0:6]
can be up to 127 bytes. Same two-call guard applied; wrapped in `if nb > 0`
to guard against nb==0 underflow (XER TBC field is 0 when no bytes to store).
dcbz: zeroes 32 bytes at a 32-byte-aligned EA — touches exactly one 128-byte
cache line; add canonical single-call invalidate guard (was entirely missing).
dcbz128: zeroes 128 bytes at a 128-byte-aligned EA — one full reservation
line; add canonical single-call invalidate guard (was entirely missing).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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