Merge remote-tracking branch 'remotes/ehabkost/tags/machine-next-pull-request' into staging

Machine queue, 2019-04-25

* 4.1 machine-types (Cornelia Huck)
* Support MAP_SYNC on pmem memory backends (Zhang Yi)
* -cpu parsing fixes and cleanups (Eduardo Habkost)
* machine initialization cleanups (Wei Yang, Markus Armbruster)

# gpg: Signature made Thu 25 Apr 2019 18:54:57 BST
# gpg:                using RSA key 2807936F984DC5A6
# gpg: Good signature from "Eduardo Habkost <ehabkost@redhat.com>" [full]
# Primary key fingerprint: 5A32 2FD5 ABC4 D3DB ACCF  D1AA 2807 936F 984D C5A6

* remotes/ehabkost/tags/machine-next-pull-request:
  util/mmap-alloc: support MAP_SYNC in qemu_ram_mmap()
  linux-headers: add linux/mman.h.
  scripts/update-linux-headers: add linux/mman.h
  util/mmap-alloc: Add a 'is_pmem' parameter to qemu_ram_mmap
  cpu: Fix crash with empty -cpu option
  cpu: Rename parse_cpu_model() to parse_cpu_option()
  vl: Simplify machine_parse()
  vl: Clean up after previous commit
  vl.c: allocate TYPE_MACHINE list once during bootup
  vl.c: make find_default_machine() local
  hw: add compat machines for 4.1

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

1 files changed, 19 insertions, 3 deletions

diff --git a/docs/nvdimm.txt b/docs/nvdimm.txt
index 7231c2d78f..b531cacd35 100644
--- a/docs/nvdimm.txt
+++ b/docs/nvdimm.txt
@@ -144,9 +144,25 @@ Guest Data Persistence
 ----------------------
 
 Though QEMU supports multiple types of vNVDIMM backends on Linux,
-currently the only one that can guarantee the guest write persistence
-is the device DAX on the real NVDIMM device (e.g., /dev/dax0.0), to
-which all guest access do not involve any host-side kernel cache.
+the only backend that can guarantee the guest write persistence is:
+
+A. DAX device (e.g., /dev/dax0.0, ) or
+B. DAX file(mounted with dax option)
+
+When using B (A file supporting direct mapping of persistent memory)
+as a backend, write persistence is guaranteed if the host kernel has
+support for the MAP_SYNC flag in the mmap system call (available
+since Linux 4.15 and on certain distro kernels) and additionally
+both 'pmem' and 'share' flags are set to 'on' on the backend.
+
+If these conditions are not satisfied i.e. if either 'pmem' or 'share'
+are not set, if the backend file does not support DAX or if MAP_SYNC
+is not supported by the host kernel, write persistence is not
+guaranteed after a system crash. For compatibility reasons, these
+conditions are ignored if not satisfied. Currently, no way is
+provided to test for them.
+For more details, please reference mmap(2) man page:
+http://man7.org/linux/man-pages/man2/mmap.2.html.
 
 When using other types of backends, it's suggested to set 'unarmed'
 option of '-device nvdimm' to 'on', which sets the unarmed flag of the