Sorry, I meant actual anonymous memory pages, not shmem. Like, anonymous
pages that are COW-shared due to fork() or KSM.
How does MTE, in general, interact with that? Assume one process ends up
modifying the tags ... and the page is COW-shared with a different
process that should not observe these tag modifications.
Tag modifications cause write faults if the page is read-only, so for
COW shared pages we would end up copying the page in the usual way,
which on arm64 would copy the tags as well via the copy_highpage hook
(see arch/arm64/mm/copypage.c).
Oh, that makes sense, thanks for pointing that out!
... and I can spot that KSM also checks the tag when de-duplicating:
pages_identical() ends up calling memcmp_pages(), which knows how to
deal with tags.
Interestingly, calc_checksum() does not seem to care about tags. But
that simply implies that pages with the same content have same checksum,
independent of the tag. And pages_identical() is the single source of truth.
--
Thanks,
David / dhildenb
