On Wed, May 17, 2023 at 1:30 AM David Hildenbrand <david@xxxxxxxxxx> wrote: > > >> Would the idea be to fail swap_readpage() on the one that comes last, > >> simply retrying to lookup the page? > > > > The idea would be that T2's arch_swap_readpage() could potentially not > > find tags if it ran after swap_free(), so T2 would produce a page > > without restored tags. But that wouldn't matter, because T1 reaching > > swap_free() means that T2 will follow the goto at [1] after waiting > > for T1 to unlock at [2], and T2's page will be discarded. > > Ah, right. > > > > >> This might be a naive question, but how does MTE play along with shared > >> anonymous pages? > > > > It should work fine. shmem_writepage() calls swap_writepage() which > > calls arch_prepare_to_swap() to write the tags. And > > shmem_swapin_folio() has a call to arch_swap_restore() to restore > > them. > > 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). Peter
