Merge remote-tracking branch 'remotes/bonzini/tags/for-upstream' into staging

Bugfixes, and reworking of the atomics documentation.

# gpg: Signature made Tue 14 Apr 2020 15:38:01 BST
# gpg:                using RSA key F13338574B662389866C7682BFFBD25F78C7AE83
# gpg:                issuer ""
# gpg: Good signature from "Paolo Bonzini <>" [full]
# gpg:                 aka "Paolo Bonzini <>" [full]
# Primary key fingerprint: 46F5 9FBD 57D6 12E7 BFD4  E2F7 7E15 100C CD36 69B1
#      Subkey fingerprint: F133 3857 4B66 2389 866C  7682 BFFB D25F 78C7 AE83

* remotes/bonzini/tags/for-upstream:
  hax: Windows doesn't like posix device names
  tests: numa: test one backend with prealloc enabled
  hostmem: set default prealloc_threads to valid value

Signed-off-by: Peter Maydell <>