From: Igor Mammedov <imammedo@redhat.com>
To: qemu-devel@nongnu.org, pbonzini@redhat.com
Subject: Re: [PATCH] Deprecate pmem=on with non-DAX capable backend file
Date: Tue, 9 Feb 2021 17:09:32 +0100 [thread overview]
Message-ID: <20210209170932.5a70136b@redhat.com> (raw)
In-Reply-To: <20210111203332.740815-1-imammedo@redhat.com>
On Mon, 11 Jan 2021 15:33:32 -0500
Igor Mammedov <imammedo@redhat.com> wrote:
> 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>
> ---
> v2:
> rephrase deprecation comment andwarning message
> (Philippe Mathieu-Daudé <philmd@redhat.com>)
Paolo,
can you pick it up via your tree?
> ---
> docs/system/deprecated.rst | 17 +++++++++++++++++
> util/mmap-alloc.c | 3 +++
> 2 files changed, 20 insertions(+)
>
> diff --git a/docs/system/deprecated.rst b/docs/system/deprecated.rst
> index bacd76d7a5..e79fb02b3a 100644
> --- a/docs/system/deprecated.rst
> +++ b/docs/system/deprecated.rst
> @@ -327,6 +327,23 @@ The Raspberry Pi machines come in various models (A, A+, B, B+). To be able
> to distinguish which model QEMU is implementing, the ``raspi2`` and ``raspi3``
> machines have been renamed ``raspi2b`` and ``raspi3b``.
>
> +Backend options
> +---------------
> +
> +Using non-persistent backing file with pmem=on (since 6.0)
> +''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
> +
> +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 27dcccd8ec..0388cc3be2 100644
> --- a/util/mmap-alloc.c
> +++ b/util/mmap-alloc.c
> @@ -20,6 +20,7 @@
> #include "qemu/osdep.h"
> #include "qemu/mmap-alloc.h"
> #include "qemu/host-utils.h"
> +#include "qemu/error-report.h"
>
> #define HUGETLBFS_MAGIC 0x958458f6
>
> @@ -166,6 +167,8 @@ void *qemu_ram_mmap(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 map failed with MAP_SHARED_VALIDATE | MAP_SYNC,
next prev parent reply other threads:[~2021-02-09 16:13 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-11 20:33 [PATCH] Deprecate pmem=on with non-DAX capable backend file Igor Mammedov
2021-01-20 19:31 ` Igor Mammedov
2021-01-20 21:35 ` Philippe Mathieu-Daudé
2021-02-09 16:09 ` Igor Mammedov [this message]
2021-04-27 20:48 ` Eduardo Habkost
2021-04-28 16:29 ` Eduardo Habkost
2021-05-03 12:14 ` Igor Mammedov
-- strict thread matches above, loose matches on Subject: below --
2020-12-29 17:29 Igor Mammedov
2020-12-29 18:04 ` Philippe Mathieu-Daudé
2020-12-29 20:11 ` Igor Mammedov
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