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

Machine queue, 2021-07-07

Deprecation:
* Deprecate pmem=on with non-DAX capable backend file
  (Igor Mammedov)

Feature:
* virtio-mem: vfio support (David Hildenbrand)

Cleanup:
* vmbus: Don't make QOM property registration conditional
  (Eduardo Habkost)

# gpg: Signature made Thu 08 Jul 2021 20:55:04 BST
# gpg:                using RSA key 5A322FD5ABC4D3DBACCFD1AA2807936F984DC5A6
# gpg:                issuer "ehabkost@redhat.com"
# 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-gl/tags/machine-next-pull-request:
  vfio: Disable only uncoordinated discards for VFIO_TYPE1 iommus
  virtio-mem: Require only coordinated discards
  softmmu/physmem: Extend ram_block_discard_(require|disable) by two discard types
  softmmu/physmem: Don't use atomic operations in ram_block_discard_(disable|require)
  vfio: Support for RamDiscardManager in the vIOMMU case
  vfio: Sanity check maximum number of DMA mappings with RamDiscardManager
  vfio: Query and store the maximum number of possible DMA mappings
  vfio: Support for RamDiscardManager in the !vIOMMU case
  virtio-mem: Implement RamDiscardManager interface
  virtio-mem: Don't report errors when ram_block_discard_range() fails
  virtio-mem: Factor out traversing unplugged ranges
  memory: Helpers to copy/free a MemoryRegionSection
  memory: Introduce RamDiscardManager for RAM memory regions
  Deprecate pmem=on with non-DAX capable backend file
  vmbus: Don't make QOM property registration conditional

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

1 files changed, 18 insertions, 0 deletions

diff --git a/docs/system/deprecated.rst b/docs/system/deprecated.rst
index 70e08baff6..94fb7dbf4e 100644
--- a/docs/system/deprecated.rst
+++ b/docs/system/deprecated.rst
@@ -221,6 +221,24 @@ This machine is deprecated because we have enough AST2500 based OpenPOWER
 machines. It can be easily replaced by the ``witherspoon-bmc`` or the
 ``romulus-bmc`` machines.
 
+Backend options
+---------------
+
+Using non-persistent backing file with pmem=on (since 6.1)
+''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
+
+This option is used when ``memory-backend-file`` is consumed by emulated NVDIMM
+device. However enabling ``memory-backend-file.pmem`` option, when backing file
+is (a) not DAX capable or (b) not on a filesystem that support direct mapping
+of persistent memory, is not safe and may lead to data loss or corruption in case
+of host crash.
+Options are:
+
+    - modify VM configuration to set ``pmem=off`` to continue using fake NVDIMM
+      (without persistence guaranties) with backing file on non DAX storage
+    - move backing file to NVDIMM storage and keep ``pmem=on``
+      (to have NVDIMM with persistence guaranties).
+
 Device options
 --------------