Roland> Yes, because the kernel may go through and unmap pages
Roland> from userspace while trying to swap. Since we have the
Roland> page locked in the kernel, the physical page won't go
Roland> anywhere, but userspace might end up with a different page
Roland> mapped at the same virtual address.
Andrew> That shouldn't happen. If get_user_pages() has elevated
Andrew> the refcount on a page then the following can happen:
...
Andrew> IOW: while the page has an elevated refcount from
Andrew> get_user_pages(), that physical page is 100% pinned.
Andrew> Once you've done the set_page_dirty+put_page(), the page
Andrew> is again under control of the VM.
Hmm... I've never tested it first hand but Libor assures me there is a
something like what I said. Libor, did I get the explanation right?
- R.
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