docs/system/deprecated.rst | 17 +++++++++++++++++ util/mmap-alloc.c | 3 +++ 2 files changed, 20 insertions(+)
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>)
---
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,
--
2.27.0
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>) I've posted as v1 though it's v2 and it looks like it fell through cracks, can someone pick it up if it looks fine, please? > --- > 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,
Cc'ing MST. On 1/20/21 8:31 PM, Igor Mammedov wrote: > 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>) > > I've posted as v1 though it's v2 and it looks like it fell through cracks, > > can someone pick it up if it looks fine, please? > >> --- >> 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, >
On Mon, Jan 11, 2021 at 03:33:32PM -0500, Igor Mammedov 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> I'm queueing this for 6.1, after changing "since 6.0" to "since 6.1". Sorry for letting it fall through the cracks. -- Eduardo
On Tue, Apr 27, 2021 at 04:48:48PM -0400, Eduardo Habkost wrote: > On Mon, Jan 11, 2021 at 03:33:32PM -0500, Igor Mammedov 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> > > I'm queueing this for 6.1, after changing "since 6.0" to "since 6.1". > > Sorry for letting it fall through the cracks. This caused build failures[1] and I had to apply the following fixup. [1] https://gitlab.com/ehabkost/qemu/-/jobs/1216917482#L3444 Signed-off-by: Eduardo Habkost <ehabkost@redhat.com> --- docs/system/deprecated.rst | 1 + 1 file changed, 1 insertion(+) diff --git a/docs/system/deprecated.rst b/docs/system/deprecated.rst index cc8d810be1a..c55c4bceb00 100644 --- a/docs/system/deprecated.rst +++ b/docs/system/deprecated.rst @@ -257,6 +257,7 @@ 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`` -- 2.30.2 -- Eduardo
On Wed, 28 Apr 2021 12:29:30 -0400 Eduardo Habkost <ehabkost@redhat.com> wrote: > On Tue, Apr 27, 2021 at 04:48:48PM -0400, Eduardo Habkost wrote: > > On Mon, Jan 11, 2021 at 03:33:32PM -0500, Igor Mammedov 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> > > > > I'm queueing this for 6.1, after changing "since 6.0" to "since 6.1". > > > > Sorry for letting it fall through the cracks. > > This caused build failures[1] and I had to apply the following > fixup. Thanks! > > [1] https://gitlab.com/ehabkost/qemu/-/jobs/1216917482#L3444 > > Signed-off-by: Eduardo Habkost <ehabkost@redhat.com> > --- > docs/system/deprecated.rst | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/docs/system/deprecated.rst b/docs/system/deprecated.rst > index cc8d810be1a..c55c4bceb00 100644 > --- a/docs/system/deprecated.rst > +++ b/docs/system/deprecated.rst > @@ -257,6 +257,7 @@ 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``
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