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>
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@ -221,6 +221,24 @@ This machine is deprecated because we have enough AST2500 based OpenPOWER
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machines. It can be easily replaced by the ``witherspoon-bmc`` or the
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machines. It can be easily replaced by the ``witherspoon-bmc`` or the
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``romulus-bmc`` machines.
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``romulus-bmc`` machines.
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Backend options
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---------------
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Using non-persistent backing file with pmem=on (since 6.1)
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''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
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This option is used when ``memory-backend-file`` is consumed by emulated NVDIMM
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device. However enabling ``memory-backend-file.pmem`` option, when backing file
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is (a) not DAX capable or (b) not on a filesystem that support direct mapping
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of persistent memory, is not safe and may lead to data loss or corruption in case
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of host crash.
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Options are:
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- modify VM configuration to set ``pmem=off`` to continue using fake NVDIMM
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(without persistence guaranties) with backing file on non DAX storage
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- move backing file to NVDIMM storage and keep ``pmem=on``
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(to have NVDIMM with persistence guaranties).
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Device options
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Device options
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--------------
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--------------
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@ -225,6 +225,8 @@ static void *mmap_activate(void *ptr, size_t size, int fd,
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"crash.\n", file_name);
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"crash.\n", file_name);
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g_free(proc_link);
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g_free(proc_link);
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g_free(file_name);
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g_free(file_name);
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warn_report("Using non DAX backing file with 'pmem=on' option"
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" is deprecated");
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}
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}
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/*
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/*
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* If mmap failed with MAP_SHARED_VALIDATE | MAP_SYNC, we will try
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* If mmap failed with MAP_SHARED_VALIDATE | MAP_SYNC, we will try
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