On Fri, May 19, 2023 at 11:21:35AM +0200, David Hildenbrand wrote: > > > 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. That was my assumption at the time, there would be a memcmp_pages() in case of checksum collision. -- Catalin
