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[PULL v2 02/15] Deprecate pmem=on with non-DAX capable backend file
From: |
Eduardo Habkost |
Subject: |
[PULL v2 02/15] Deprecate pmem=on with non-DAX capable backend file |
Date: |
Thu, 8 Jul 2021 15:55:39 -0400 |
From: Igor Mammedov <imammedo@redhat.com>
It is not safe to pretend that emulated NVDIMM supports
persistence while backend actually failed to enable it
and used non-persistent mapping as fall back.
Instead of falling-back, QEMU should be more strict and
error out with clear message that it's not supported.
So if user asks for persistence (pmem=on), they should
store backing file on NVDIMM.
Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20210111203332.740815-1-imammedo@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
---
docs/system/deprecated.rst | 18 ++++++++++++++++++
util/mmap-alloc.c | 2 ++
2 files changed, 20 insertions(+)
diff --git a/docs/system/deprecated.rst b/docs/system/deprecated.rst
index 70e08baff62..94fb7dbf4e6 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
--------------
diff --git a/util/mmap-alloc.c b/util/mmap-alloc.c
index 838e286ce51..893d864354a 100644
--- a/util/mmap-alloc.c
+++ b/util/mmap-alloc.c
@@ -225,6 +225,8 @@ static void *mmap_activate(void *ptr, size_t size, int fd,
"crash.\n", file_name);
g_free(proc_link);
g_free(file_name);
+ warn_report("Using non DAX backing file with 'pmem=on' option"
+ " is deprecated");
}
/*
* If mmap failed with MAP_SHARED_VALIDATE | MAP_SYNC, we will try
--
2.31.1
- [PULL v2 00/15] Machine queue, 2021-07-07, Eduardo Habkost, 2021/07/08
- [PULL v2 02/15] Deprecate pmem=on with non-DAX capable backend file,
Eduardo Habkost <=
- [PULL v2 01/15] vmbus: Don't make QOM property registration conditional, Eduardo Habkost, 2021/07/08
- [PULL v2 03/15] memory: Introduce RamDiscardManager for RAM memory regions, Eduardo Habkost, 2021/07/08
- [PULL v2 04/15] memory: Helpers to copy/free a MemoryRegionSection, Eduardo Habkost, 2021/07/08
- [PULL v2 05/15] virtio-mem: Factor out traversing unplugged ranges, Eduardo Habkost, 2021/07/08
- [PULL v2 06/15] virtio-mem: Don't report errors when ram_block_discard_range() fails, Eduardo Habkost, 2021/07/08
- [PULL v2 07/15] virtio-mem: Implement RamDiscardManager interface, Eduardo Habkost, 2021/07/08
- [PULL v2 08/15] vfio: Support for RamDiscardManager in the !vIOMMU case, Eduardo Habkost, 2021/07/08
- [PULL v2 09/15] vfio: Query and store the maximum number of possible DMA mappings, Eduardo Habkost, 2021/07/08
- [PULL v2 10/15] vfio: Sanity check maximum number of DMA mappings with RamDiscardManager, Eduardo Habkost, 2021/07/08
- [PULL v2 11/15] vfio: Support for RamDiscardManager in the vIOMMU case, Eduardo Habkost, 2021/07/08