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Userfaultfd – Create a file descriptor for handling page faults in user space

by phab on 2/10/22, 12:49 PM with 15 comments

• by annonacct38 on 2/10/22, 4:55 PM

  One of my favorite examples of userfaultfd: transparently mapping databases on cloud storage into RAM.

  https://tech.nextroll.com/blog/data/2016/11/29/traildb-mmap-...

• by Retr0id on 2/10/22, 3:19 PM

  A fun application of userfaultfd:

  https://github.com/whitequark/unfork

  Past discussions of unfork:

  https://news.ycombinator.com/item?id=21394678

  https://news.ycombinator.com/item?id=27287930

• by rwmj on 2/10/22, 2:45 PM

  It's a great feature, but it had a few unintended side-effects:

  https://lwn.net/Articles/819834/ "Blocking userfaultfd() kernel-fault handling" (patches to fix a security issue, more detail in https://duasynt.com/blog/linux-kernel-heap-spray)

  https://lwn.net/Articles/849876/ "Patching until the COWs come home" (complicated interaction with copy-on-write)

• by mattgreenrocks on 2/10/22, 3:55 PM

  Possibly dumb question, but if I have some code that tries to blindly jump to, say, address 0x4000, would userfaultfd let me redirect accesses to 0x4000 to an address I've allocated elsewhere?