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Here's the full flow: >>>>>> >>>>>> getsockopt(TCP_ZEROCOPY_RECEIVE) returns -EINVAL because of the >>>>>> below flow in the kernel: >>>>>> >>>>>> tcp_zerocopy_receive() >>>>>> -> tcp_zerocopy_vm_insert_batch() >>>>>> -> vm_insert_pages() >>>>>> -> insert_pages() >>>>>> -> insert_page_in_batch_locked() >>>>>> -> validate_page_before_insert() returns -EINVAL >>>>>> because page_has_type(page) is now true. >>>>>> >>>>>> The patch below fixes the issue. But is this a valid fix? >>>>> >>>>> Hmm the check traces back to commit 0ee930e6cafa0 "mm/memory.c: prevent >>>>> mapping typed pages to userspace" >>>>> >>>>>> Pages which use page_type must never be mapped to userspace as it would >>>>>> destroy their page type. Add an explicit check for this instead of >>>>>> assuming that kernel drivers always get this right. >>>>> >>>>> So uh, this doesn't look good I think. >>>> >>>> Yep, you fundamentally can't map a page with a type as page type aliases with >>>> mapcount. Even with the given diff, just mapping it will increment the mapcount >>>> and wreak havoc. I think we need to revert this patch for now. >>>> >>>> I'm not sure what the long term plan for this would be. If page types are moved >>>> to memdesc types, then the two stop colliding and that could work. I don't know >>>> if that's Willy's plan, however. >>>> >>>> (then there's the other question: are page pool pages really folios? not really. >>>> they are mappable, but they aren't part of the page cache, or anon, nor are >>>> they in the LRU or have rmap capabilities. perhaps we need a different memdesc >>>> for those. we're one step away from reinventing class polymorphism from first >>>> principles ;) >>> >>> Zi Yan is working on this: non-folio pages would no longer mess with >>> rmap/mapcounts, and page table walking code will identify them to be non-folio >>> things to skip them. >>> >>> It will take a while, though ... >>> >> So do I get it right that the path forward here is to revert this commit [1] >> and wait until the work from Zi Yan is ready? > > I think it's the best way for now. > Ack. Can you do it please? This is a more complicated revert and the risk that I mess it up is higher. Thanks, Dragos