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

* New KVM PV features (Marcelo, Wanpeng)
* valgrind fixes (Andrey)
* Remove clock reset notifiers (David)
* KConfig and Makefile cleanups (Paolo)
* Replay and icount improvements (Pavel)
* x86 FP fixes (Peter M.)
* TCG locking assertions (Roman)
* x86 support for mmap-ed -kernel/-initrd (Stefano)
* Other cleanups (Wei Yang, Yan Zhao, Tony)
* LSI fix for infinite loop (Prasad)
* ARM migration fix (Catherine)
* AVX512_BF16 feature (Jing)

# gpg: Signature made Tue 20 Aug 2019 19:00:54 BST
# gpg:                using RSA key BFFBD25F78C7AE83
# gpg: Good signature from "Paolo Bonzini <bonzini@gnu.org>" [full]
# gpg:                 aka "Paolo Bonzini <pbonzini@redhat.com>" [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: (33 commits)
  x86: Intel AVX512_BF16 feature enabling
  scsi: lsi: exit infinite loop while executing script (CVE-2019-12068)
  test-bitmap: test set 1 bit case for bitmap_set
  migration: do not rom_reset() during incoming migration
  HACKING: Document 'struct' keyword usage
  kvm: vmxcap: Enhance with latest features
  cpus-common: nuke finish_safe_work
  icount: remove unnecessary gen_io_end calls
  icount: clean up cpu_can_io at the entry to the block
  replay: rename step-related variables and functions
  replay: refine replay-time module
  replay: fix replay shutdown
  util/qemu-timer: refactor deadline calculation for external timers
  replay: document development rules
  replay: add missing fix for internal function
  timer: last, remove last bits of last
  replay: Remove host_clock_last
  timer: Remove reset notifiers
  mc146818rtc: Remove reset notifiers
  memory: fix race between TCG and accesses to dirty bitmap
  ...

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

1 files changed, 46 insertions, 0 deletions

diff --git a/docs/devel/replay.txt b/docs/devel/replay.txt
new file mode 100644
index 0000000..e641c35
--- /dev/null
+++ b/docs/devel/replay.txt
@@ -0,0 +1,46 @@
+Record/replay mechanism, that could be enabled through icount mode, expects
+the virtual devices to satisfy the following requirements.
+
+The main idea behind this document is that everything that affects
+the guest state during execution in icount mode should be deterministic.
+
+Timers
+======
+
+All virtual devices should use virtual clock for timers that change the guest
+state. Virtual clock is deterministic, therefore such timers are deterministic
+too.
+
+Virtual devices can also use realtime clock for the events that do not change
+the guest state directly. When the clock ticking should depend on VM execution
+speed, use virtual clock with EXTERNAL attribute. It is not deterministic,
+but its speed depends on the guest execution. This clock is used by
+the virtual devices (e.g., slirp routing device) that lie outside the
+replayed guest.
+
+Bottom halves
+=============
+
+Bottom half callbacks, that affect the guest state, should be invoked through
+replay_bh_schedule_event or replay_bh_schedule_oneshot_event functions.
+Their invocations are saved in record mode and synchronized with the existing
+log in replay mode.
+
+Saving/restoring the VM state
+=============================
+
+All fields in the device state structure (including virtual timers)
+should be restored by loadvm to the same values they had before savevm.
+
+Avoid accessing other devices' state, because the order of saving/restoring
+is not defined. It means that you should not call functions like
+'update_irq' in post_load callback. Save everything explicitly to avoid
+the dependencies that may make restoring the VM state non-deterministic.
+
+Stopping the VM
+===============
+
+Stopping the guest should not interfere with its state (with the exception
+of the network connections, that could be broken by the remote timeouts).
+VM can be stopped at any moment of replay by the user. Restarting the VM
+after that stop should not break the replay by the unneeded guest state change.