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| author | Igor Mammedov <imammedo@redhat.com> | 2021-01-11 15:33:32 -0500 |
|---|---|---|
| committer | Eduardo Habkost <ehabkost@redhat.com> | 2021-07-06 18:05:16 -0400 |
| commit | cdcf766d0b0364165ba9e5ceacfdf37c8b1fe4ae (patch) | |
| tree | 27dae453b720de1bc58c6eb425f9efbf996f9b3e | |
| parent | 80cc1a0dd19cc414ddaa3f1b9b6ef91e3ebc12b2 (diff) | |
| download | focaccia-qemu-cdcf766d0b0364165ba9e5ceacfdf37c8b1fe4ae.tar.gz focaccia-qemu-cdcf766d0b0364165ba9e5ceacfdf37c8b1fe4ae.zip | |
Deprecate pmem=on with non-DAX capable backend file
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>
| -rw-r--r-- | docs/system/deprecated.rst | 18 | ||||
| -rw-r--r-- | util/mmap-alloc.c | 2 |
2 files changed, 20 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 -------------- diff --git a/util/mmap-alloc.c b/util/mmap-alloc.c index 838e286ce5..893d864354 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 |