From cdcf766d0b0364165ba9e5ceacfdf37c8b1fe4ae Mon Sep 17 00:00:00 2001 From: Igor Mammedov Date: Mon, 11 Jan 2021 15:33:32 -0500 Subject: Deprecate pmem=on with non-DAX capable backend file MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 Reviewed-by: Philippe Mathieu-Daudé Message-Id: <20210111203332.740815-1-imammedo@redhat.com> Signed-off-by: Eduardo Habkost --- docs/system/deprecated.rst | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) (limited to 'docs') diff --git a/docs/system/deprecated.rst b/docs/system/deprecated.rst index 70e08ba..94fb7db 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 -------------- -- cgit v1.1