v2 changelog:
- Fix Mac (and possibly some other) build issues for two patches
- os: add an ability to lock memory on_fault
- memory: pass MemTxAttrs to memory_access_is_direct()
List of features:
- William's fix on ram hole punching when with file offset
- Daniil's patchset to introduce mem-lock=on-fault
- William's hugetlb hwpoison fix for size report & remap
- David's series to allow qemu debug writes to MMIOs
-----BEGIN PGP SIGNATURE-----
iIgEABYKADAWIQS5GE3CDMRX2s990ak7X8zN86vXBgUCZ6zcQBIccGV0ZXJ4QHJl
ZGhhdC5jb20ACgkQO1/MzfOr1wbL3wEAqx94NpB/tEEBj6WXE3uV9LqQ0GCTYmV+
MbM51Vep8ksA/35yFn3ltM2yoSnUf9WJW6LXEEKhQlwswI0vChQERgkE
=++O1
-----END PGP SIGNATURE-----
Merge tag 'mem-next-pull-request' of https://gitlab.com/peterx/qemu into staging
Memory pull request for 10.0
v2 changelog:
- Fix Mac (and possibly some other) build issues for two patches
- os: add an ability to lock memory on_fault
- memory: pass MemTxAttrs to memory_access_is_direct()
List of features:
- William's fix on ram hole punching when with file offset
- Daniil's patchset to introduce mem-lock=on-fault
- William's hugetlb hwpoison fix for size report & remap
- David's series to allow qemu debug writes to MMIOs
# -----BEGIN PGP SIGNATURE-----
#
# iIgEABYKADAWIQS5GE3CDMRX2s990ak7X8zN86vXBgUCZ6zcQBIccGV0ZXJ4QHJl
# ZGhhdC5jb20ACgkQO1/MzfOr1wbL3wEAqx94NpB/tEEBj6WXE3uV9LqQ0GCTYmV+
# MbM51Vep8ksA/35yFn3ltM2yoSnUf9WJW6LXEEKhQlwswI0vChQERgkE
# =++O1
# -----END PGP SIGNATURE-----
# gpg: Signature made Thu 13 Feb 2025 01:37:04 HKT
# gpg: using EDDSA key B9184DC20CC457DACF7DD1A93B5FCCCDF3ABD706
# gpg: issuer "peterx@redhat.com"
# gpg: Good signature from "Peter Xu <xzpeter@gmail.com>" [full]
# gpg: aka "Peter Xu <peterx@redhat.com>" [full]
# Primary key fingerprint: B918 4DC2 0CC4 57DA CF7D D1A9 3B5F CCCD F3AB D706
* tag 'mem-next-pull-request' of https://gitlab.com/peterx/qemu:
overcommit: introduce mem-lock=on-fault
system: introduce a new MlockState enum
system/vl: extract overcommit option parsing into a helper
os: add an ability to lock memory on_fault
system/physmem: poisoned memory discard on reboot
system/physmem: handle hugetlb correctly in qemu_ram_remap()
physmem: teach cpu_memory_rw_debug() to write to more memory regions
hmp: use cpu_get_phys_page_debug() in hmp_gva2gpa()
memory: pass MemTxAttrs to memory_access_is_direct()
physmem: disallow direct access to RAM DEVICE in address_space_write_rom()
physmem: factor out direct access check into memory_region_supports_direct_access()
physmem: factor out RAM/ROMD check in memory_access_is_direct()
physmem: factor out memory_region_is_ram_device() check in memory_access_is_direct()
system/physmem: take into account fd_offset for file fallocate
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
qmp_migrate guarantees that cpr_channel is not null for
MIG_MODE_CPR_TRANSFER when cpr_state_save is called:
qmp_migrate()
if (s->parameters.mode == MIG_MODE_CPR_TRANSFER && !cpr_channel) {
return;
}
cpr_state_save(cpr_channel)
but cpr_state_save checks for mode differently before using channel,
and Coverity cannot infer that they are equivalent in outgoing QEMU,
and warns that channel may be NULL:
cpr_state_save(channel)
MigMode mode = migrate_mode();
if (mode == MIG_MODE_CPR_TRANSFER) {
f = cpr_transfer_output(channel, errp);
To make Coverity happy, assert that channel != NULL in cpr_state_save.
Resolves: Coverity CID 1590980
Reported-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
Message-ID: <1738788841-211843-1-git-send-email-steven.sistare@oracle.com>
[assert instead of using parameters.mode in cpr_state_save]
Signed-off-by: Fabiano Rosas <farosas@suse.de>
The expected outcome from qmp_migrate_cancel() is that the source
migration goes to the terminal state
MIGRATION_STATUS_CANCELLED. Anything different from this is a bug when
cancelling.
Make sure there is never a state transition from an unspecified state
into FAILED. Code that sets FAILED, should always either make sure
that the old state is not CANCELLING or specify the old state.
Note that the destination is allowed to go into FAILED, so there's no
issue there.
(I don't think this is relevant as a backport because cancelling does
work, it just doesn't show the right state at the end)
Fixes: 3dde8fdbad ("migration: Merge precopy/postcopy on switchover start")
Fixes: d0edb8a173 ("migration: Create the postcopy preempt channel asynchronously")
Fixes: 8518278a6a ("migration: implementation of background snapshot thread")
Fixes: bf78a046b9 ("migration: refactor migrate_fd_connect failures")
Reviewed-by: Peter Xu <peterx@redhat.com>
Message-ID: <20250213175927.19642-7-farosas@suse.de>
Signed-off-by: Fabiano Rosas <farosas@suse.de>
After postcopy has started, it's not possible to recover the source
machine in case a migration error occurs because the destination has
already been changing the state of the machine. For that same reason,
it doesn't make sense to try to cancel the migration after postcopy
has started. Reject the cancel command during postcopy.
Reviewed-by: Peter Xu <peterx@redhat.com>
Message-ID: <20250213175927.19642-6-farosas@suse.de>
Signed-off-by: Fabiano Rosas <farosas@suse.de>
If the destination side fails at migration_ioc_process_incoming()
before starting the coroutine, it will report the error but QEMU will
not exit.
Set the migration state to FAILED and exit the process if
exit-on-error allows.
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2633
Reported-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Message-ID: <20250213175927.19642-5-farosas@suse.de>
Signed-off-by: Fabiano Rosas <farosas@suse.de>
Remove all instances of _fd_ from the migration generic code. These
functions have grown over time and the _fd_ part is now just
confusing.
migration_fd_error() -> migration_error() makes it a little
vague. Since it's only used for migration_connect() failures, change
it to migration_connect_set_error().
Reviewed-by: Peter Xu <peterx@redhat.com>
Message-ID: <20250213175927.19642-4-farosas@suse.de>
Signed-off-by: Fabiano Rosas <farosas@suse.de>
There's no need for two separate functions and this _fd_ is a historic
artifact that makes little sense nowadays.
Reviewed-by: Peter Xu <peterx@redhat.com>
Message-ID: <20250213175927.19642-3-farosas@suse.de>
Signed-off-by: Fabiano Rosas <farosas@suse.de>
There's no point passing the error into migration cancel only for it
to call migrate_set_error().
Reviewed-by: Peter Xu <peterx@redhat.com>
Message-ID: <20250213175927.19642-2-farosas@suse.de>
Signed-off-by: Fabiano Rosas <farosas@suse.de>
We're currently only checking the QEMUFile error after
qemu_loadvm_state(). This was causing a TLS termination error from
multifd recv threads to be ignored.
Start checking the migration error as well to avoid missing further
errors.
Regarding compatibility concerning the TLS termination error that was
being ignored, for QEMUs <= 9.2 - if the old QEMU is being used as
migration source - the recently added migration property
multifd-tls-clean-termination needs to be set to OFF in the
*destination* machine.
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Fabiano Rosas <farosas@suse.de>
We're currently changing the way the source multifd migration handles
the shutdown of the multifd channels when TLS is in use to perform a
clean termination by calling gnutls_bye().
Older src QEMUs will always close the channel without terminating the
TLS session. New dst QEMUs treat an unclean termination as an error.
Add multifd_clean_tls_termination (default true) that can be switched
on the destination whenever a src QEMU <= 9.2 is in use.
(Note that the compat property is only strictly necessary for src
QEMUs older than 9.1. Due to synchronization coincidences, src QEMUs
9.1 and 9.2 can put the destination in a condition where it doesn't
see the unclean termination. Still, make the property more inclusive
to facilitate potential backports.)
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Fabiano Rosas <farosas@suse.de>
The multifd recv side has been getting a TLS error of
GNUTLS_E_PREMATURE_TERMINATION at the end of migration when the send
side closes the sockets without ending the TLS session. This has been
masked by the code not checking the migration error after loadvm.
Start ending the TLS session at multifd_send_shutdown() so the recv
side always sees a clean termination (EOF) and we can start to
differentiate that from an actual premature termination that might
possibly happen in the middle of the migration.
There's nothing to be done if a previous migration error has already
broken the connection, so add a comment explaining it and ignore any
errors coming from gnutls_bye().
This doesn't break compat with older recv-side QEMUs because EOF has
always caused the recv thread to exit cleanly.
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Fabiano Rosas <farosas@suse.de>
Locking the memory without MCL_ONFAULT instantly prefaults any mmaped
anonymous memory with a write-fault, which introduces a lot of extra
overhead in terms of memory usage when all you want to do is to prevent
kcompactd from migrating and compacting QEMU pages. Add an option to
only lock pages lazily as they're faulted by the process by using
MCL_ONFAULT if asked.
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Daniil Tatianin <d-tatianin@yandex-team.ru>
Link: https://lore.kernel.org/r/20250212143920.1269754-5-d-tatianin@yandex-team.ru
Signed-off-by: Peter Xu <peterx@redhat.com>
Replace the boolean value enable_mlock with an enum and add a helper to
decide whether we should be calling os_mlock.
This is a stepping stone towards introducing a new mlock mode, which
will be the third possible state of this enum.
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Daniil Tatianin <d-tatianin@yandex-team.ru>
Link: https://lore.kernel.org/r/20250212143920.1269754-4-d-tatianin@yandex-team.ru
Signed-off-by: Peter Xu <peterx@redhat.com>
This will be used in the following commits to make it possible to only
lock memory on fault instead of right away.
Signed-off-by: Daniil Tatianin <d-tatianin@yandex-team.ru>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Link: https://lore.kernel.org/r/20250212143920.1269754-2-d-tatianin@yandex-team.ru
[peterx: fail os_mlock(on_fault=1) when not supported]
[peterx: use G_GNUC_UNUSED instead of "(void)on_fault", per Dan]
Signed-off-by: Peter Xu <peterx@redhat.com>
The general expectation is that header files should follow the same
file/path naming scheme as the corresponding source file. There are
various historical exceptions to this practice in QEMU, with one of
the most notable being the include/qapi/qmp/ directory. Most of the
headers there correspond to source files in qobject/.
This patch corrects most of that inconsistency by creating
include/qobject/ and moving the headers for qobject/ there.
This also fixes MAINTAINERS for include/qapi/qmp/dispatch.h:
scripts/get_maintainer.pl now reports "QAPI" instead of "No
maintainers found".
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Zhao Liu <zhao1.liu@intel.com>
Acked-by: Halil Pasic <pasic@linux.ibm.com> #s390x
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-ID: <20241118151235.2665921-2-armbru@redhat.com>
[Rebased]
Block devices have an individual active state, a single global flag
can't cover this correctly. This becomes more important as we allow
users to manually manage which nodes are active or inactive.
Now that it's allowed to call bdrv_inactivate_all() even when some
nodes are already inactive, we can remove the flag and just
unconditionally call bdrv_inactivate_all() and, more importantly,
bdrv_activate_all() before we make use of the nodes.
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Acked-by: Fabiano Rosas <farosas@suse.de>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-ID: <20250204211407.381505-5-kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Refactor ram_save_target_page legacy and multifd
functions into one. Other than simplifying it,
it frees 'migration_ops' object from usage, so it
is expunged.
Signed-off-by: Prasad Pandit <pjp@fedoraproject.org>
Reviewed-by: Fabiano Rosas <farosas@suse.de>
Message-ID: <20250127120823.144949-3-ppandit@redhat.com>
Signed-off-by: Fabiano Rosas <farosas@suse.de>
Two small cleanups in the same section of vmstate_save():
- Check vmdesc before the "mixed null/non-null data in array" logic, to
be crystal clear that it's only about the JSON writer, not the vmstate on
its own in the migration stream.
- Since we have is_null variable now, use that to replace a check.
Signed-off-by: Peter Xu <peterx@redhat.com>
Tested-by: Jiri Denemark <jdenemar@redhat.com>
Reviewed-by: Juraj Marcin <jmarcin@redhat.com>
Link: https://lore.kernel.org/r/20250114230746.3268797-17-peterx@redhat.com
Signed-off-by: Fabiano Rosas <farosas@suse.de>
Now after all the cleanups, finally we can merge the switchover startup
phase into one single function for precopy/postcopy.
Signed-off-by: Peter Xu <peterx@redhat.com>
Tested-by: Jiri Denemark <jdenemar@redhat.com>
Reviewed-by: Juraj Marcin <jmarcin@redhat.com>
Link: https://lore.kernel.org/r/20250114230746.3268797-16-peterx@redhat.com
Signed-off-by: Fabiano Rosas <farosas@suse.de>
DEVICE state was introduced back in 2017:
https://lore.kernel.org/qemu-devel/20171020090556.18631-1-dgilbert@redhat.com/
Quote from Dave's cover letter, when the pre-switchover phase was enabled,
the state transition looks like this:
The precopy flow is:
active->pre-switchover->device->completed
The postcopy flow is:
active->pre-switchover->postcopy-active->completed
To supplement above, when the cap is not enabled:
The precopy flow is:
active->completed
The postcopy flow is:
active->postcopy-active->completed
It works for us, though we have some code just to special case these state
transitions, so the DEVICE state currently is special only to precopy, and
only conditionally.
I had a quick discussion with Libvirt developers, it turns out that this
may not be necessary. IOW, it seems okay we can have DEVICE state to be
generic, so that we don't have over-complicated state machines. It not
only helps align all the migration state machine, help cleanup the code
path especially on pre-switchover handling (see the patch itself), another
side benefit is we can unconditionally have a specific state to mark the
switchover phase, which might be helpful for debugging too.
This patch makes the DEVICE state to be present always, marking that source
QEMU is switching over. Then the state machine will be always as simple
as:
active-> [pre-switchover->] -> device -> [postcopy-active->] -> complete
After the change, no matter whether pre-switchover or postcopy is enabled
or not, we always have DEVICE state showing the switchover phase. When
pre-switchover enabled, we'll have an extra stage before that. When
postcopy is enabled, we'll have an extra stage after that.
A few qtests need touch up in QEMU tree for this change:
- A few iotest outputs (194, 203, 234, 262, 280)
- Teach libqos's migrate() on "device" state
Cc: Jiri Denemark <jdenemar@redhat.com>
Cc: Daniel P. Berrangé <berrange@redhat.com>
Cc: Dr. David Alan Gilbert <dave@treblig.org>
Signed-off-by: Peter Xu <peterx@redhat.com>
Tested-by: Jiri Denemark <jdenemar@redhat.com>
Reviewed-by: Juraj Marcin <jmarcin@redhat.com>
Link: https://lore.kernel.org/r/20250114230746.3268797-15-peterx@redhat.com
Signed-off-by: Fabiano Rosas <farosas@suse.de>
Now qemu_savevm_state_complete_precopy() is never used in postcopy, clean
it up as in_postcopy==false now unconditionally.
Signed-off-by: Peter Xu <peterx@redhat.com>
Tested-by: Jiri Denemark <jdenemar@redhat.com>
Reviewed-by: Juraj Marcin <jmarcin@redhat.com>
Link: https://lore.kernel.org/r/20250114230746.3268797-14-peterx@redhat.com
Signed-off-by: Fabiano Rosas <farosas@suse.de>
Postcopy invokes qemu_savevm_state_complete_precopy() twice for a long
time, and that caused way too much confusions. Let's clean this up and
make postcopy easier to read.
It's actually fairly straightforward: postcopy starts with saving
non-postcopiable iterables, then later it saves again with non-iterable
only. Move these two calls out makes everything much easier to follow.
Otherwise it's very unclear what qemu_savevm_state_complete_precopy() did
in either of the calls.
No functional change intended.
Signed-off-by: Peter Xu <peterx@redhat.com>
Tested-by: Jiri Denemark <jdenemar@redhat.com>
Reviewed-by: Juraj Marcin <jmarcin@redhat.com>
Link: https://lore.kernel.org/r/20250114230746.3268797-13-peterx@redhat.com
Signed-off-by: Fabiano Rosas <farosas@suse.de>
Postcopy invokes qemu_savevm_state_complete_precopy() twice, that means
it'll invoke COMPLETE notify twice.. also twice the tracepoints that
marking precopy complete.
Move that notification (along with the tracepoint) out to the caller, so
that postcopy will only notify once right at the start of switchover phase
from precopy. When at it, rename it to suite the file now it locates.
For precopy, there should have no functional change except the tracepoint
has a name change.
For the other two users of qemu_savevm_state_complete_precopy(), namely:
qemu_savevm_state() and qemu_savevm_live_state(): the notifier shouldn't
matter because they're not precopy at all. Now in these two contexts (aka,
"savevm", and "colo") sometimes the precopy notifiers will still be
invoked, but that's outside the scope of this patch.
Signed-off-by: Peter Xu <peterx@redhat.com>
Tested-by: Jiri Denemark <jdenemar@redhat.com>
Reviewed-by: Juraj Marcin <jmarcin@redhat.com>
Link: https://lore.kernel.org/r/20250114230746.3268797-12-peterx@redhat.com
Signed-off-by: Fabiano Rosas <farosas@suse.de>
This paves way for some follow up patch to modify migration states at the
end of postcopy_start(), which should better be with the BQL so that
there's no way of concurrent cancellation.
So we'll do something slightly more with BQL but they're really trivial,
hopefully nothing will really chance with this.
A side benefit is we can drop another explicit lock() in failure path.
Signed-off-by: Peter Xu <peterx@redhat.com>
Tested-by: Jiri Denemark <jdenemar@redhat.com>
Reviewed-by: Juraj Marcin <jmarcin@redhat.com>
Link: https://lore.kernel.org/r/20250114230746.3268797-11-peterx@redhat.com
Signed-off-by: Fabiano Rosas <farosas@suse.de>
I can't see why we must cache the state now after we avoided possible
CANCEL race: that's the only thing I can think of that can modify the
migration state concurrently with the migration thread itself. Make all
the state updates to happen always, then we don't need to cache the state
anymore.
Signed-off-by: Peter Xu <peterx@redhat.com>
Tested-by: Jiri Denemark <jdenemar@redhat.com>
Reviewed-by: Juraj Marcin <jmarcin@redhat.com>
Link: https://lore.kernel.org/r/20250114230746.3268797-10-peterx@redhat.com
Signed-off-by: Fabiano Rosas <farosas@suse.de>
In migration_maybe_pause() QEMU may yield BQL before waiting for a
semaphore. However it yields the BQL too early, which logically gives it
chance for the main thread to quickly take the BQL and modify the state to
CANCELLING.
To avoid such race condition from happening at all, always update the
migration states within the BQL. It'll make sure no concurrent
cancellation can ever happen.
With that, IIUC there's chance we can remove the extra parameter in
migration_maybe_pause() to update active state, but that'll be done
separately later.
Signed-off-by: Peter Xu <peterx@redhat.com>
Tested-by: Jiri Denemark <jdenemar@redhat.com>
Reviewed-by: Juraj Marcin <jmarcin@redhat.com>
Link: https://lore.kernel.org/r/20250114230746.3268797-9-peterx@redhat.com
Signed-off-by: Fabiano Rosas <farosas@suse.de>
Precopy uses unlimited bandwidth always during switchover, it makes sense
because this is so critical and no one would like to throttle bandwidth
during the VM blackout.
OTOH, postcopy surprisingly didn't do that. There's one line that in the
middle of the postcopy switchover it tries to switch to postcopy's
specified max-postcopy-bandwidth, but even so it's somewhere in the middle
which is strange.
This patch brings the two modes to always use unlimited bandwidth for
switchover, meanwhile only apply the postcopy max bandwidth after the
switchover is completed.
Signed-off-by: Peter Xu <peterx@redhat.com>
Tested-by: Jiri Denemark <jdenemar@redhat.com>
Reviewed-by: Juraj Marcin <jmarcin@redhat.com>
Link: https://lore.kernel.org/r/20250114230746.3268797-8-peterx@redhat.com
Signed-off-by: Fabiano Rosas <farosas@suse.de>
Do one shot cpu sync at qemu_savevm_state_complete_precopy_non_iterable(),
instead of coding it separately in two places.
Note that in the context of qemu_savevm_state_complete_precopy(), this
patch is also an optimization for postcopy path, in that we can avoid sync
cpu twice during switchover: before this patch, postcopy_start() invokes
twice on qemu_savevm_state_complete_precopy(), each of them will try to
sync CPU info. In reality, only one of them would be enough.
For background snapshot, there's no intended functional change.
Signed-off-by: Peter Xu <peterx@redhat.com>
Tested-by: Jiri Denemark <jdenemar@redhat.com>
Reviewed-by: Juraj Marcin <jmarcin@redhat.com>
Link: https://lore.kernel.org/r/20250114230746.3268797-7-peterx@redhat.com
Signed-off-by: Fabiano Rosas <farosas@suse.de>
This parameter is only used by one caller, which is the genuine precopy
complete path (migration_completion_precopy).
The parameter was introduced in a1fbe750fd ("migration: Fix race of image
locking between src and dst") to make sure the inactivate will happen
before EOF to make sure dest will always be able to activate the disk
properly. However there's no limitation on how early we inactivate the
disk. For precopy completion path, we can always do that as long as VM is
stopped.
Move the disk inactivate there, then we can remove this inactivate_disk
parameter in the whole call stack, because all the rest users pass in false
always.
Signed-off-by: Peter Xu <peterx@redhat.com>
Tested-by: Jiri Denemark <jdenemar@redhat.com>
Reviewed-by: Juraj Marcin <jmarcin@redhat.com>
Link: https://lore.kernel.org/r/20250114230746.3268797-6-peterx@redhat.com
Signed-off-by: Fabiano Rosas <farosas@suse.de>
Postcopy can trigger this tracepoint twice, while only the 1st one is
valid. Avoid triggering the 2nd tracepoint just like what we do with
recording the total downtime.
Signed-off-by: Peter Xu <peterx@redhat.com>
Tested-by: Jiri Denemark <jdenemar@redhat.com>
Reviewed-by: Juraj Marcin <jmarcin@redhat.com>
Link: https://lore.kernel.org/r/20250114230746.3268797-5-peterx@redhat.com
Signed-off-by: Fabiano Rosas <farosas@suse.de>
postcopy_start() is the entry function that postcopy is destined to start.
It also means QEMU source will not dump VM description, aka, the JSON
writer is garbage now.
We can leave that to be cleaned up when migration completes, however when
with the JSON writer object being present, vmstate_save() will still try to
construct the JSON objects for the VM descriptions, even though it'll never
be used later if it's postcopy.
To save those cycles, release the JSON writer earlier for postcopy. Then
vmstate_save() later will be smart enough to skip the JSON object
constructions completely. It can logically reduce downtime because all
such JSON constructions happen during postcopy blackout.
Signed-off-by: Peter Xu <peterx@redhat.com>
Tested-by: Jiri Denemark <jdenemar@redhat.com>
Reviewed-by: Juraj Marcin <jmarcin@redhat.com>
Link: https://lore.kernel.org/r/20250114230746.3268797-4-peterx@redhat.com
Signed-off-by: Fabiano Rosas <farosas@suse.de>
QEMU machine has a property "suppress-vmdesc". When it is enabled, QEMU
will stop attaching JSON VM description at the end of the precopy migration
stream (postcopy is never affected because postcopy never attach that).
However even if it's suppressed by the user, the source QEMU will still
construct the JSON descriptions, which is a complete waste of CPU and
memory resources.
To avoid it, only create the JSON writer object if suppress-vmdesc is not
specified.
Luckily, vmstate_save() already supports vmdesc==NULL, so only a few spots
that are left to be prepared that vmdesc can be NULL now.
When at it, move the init / destroy of the JSON writer object to start /
end of the migration - the JSON writer object is a sub-struct of migration
state, and that looks like the only object that was dynamically allocated /
destroyed within migration process. Make it the same as the rest objects
that migration uses.
Signed-off-by: Peter Xu <peterx@redhat.com>
Tested-by: Jiri Denemark <jdenemar@redhat.com>
Reviewed-by: Juraj Marcin <jmarcin@redhat.com>
Link: https://lore.kernel.org/r/20250114230746.3268797-3-peterx@redhat.com
Signed-off-by: Fabiano Rosas <farosas@suse.de>
should_send_vmdesc() has a hack inside (which was not reflected in the
function name) in that it tries to detect global postcopy state and that
will affect the value to be returned.
It's easier to keep the helper simple by only check the suppress-vmdesc
property. Then:
- On the sender side of its usage, there's already in_postcopy variable
that we can use: postcopy doesn't send vmdesc at all, so directly skip
everything for postcopy.
- On the recv side, when reaching vmdesc processing it must be precopy
code already, hence that hack check never used to work anyway.
No functional change intended, except a trivial side effect that QEMU
source will start to avoid running some JSON helper in postcopy path, but
that would only reduce the postcopy blackout window a bit, rather than any
other bad side effect.
Signed-off-by: Peter Xu <peterx@redhat.com>
Tested-by: Jiri Denemark <jdenemar@redhat.com>
Reviewed-by: Juraj Marcin <jmarcin@redhat.com>
Link: https://lore.kernel.org/r/20250114230746.3268797-2-peterx@redhat.com
Signed-off-by: Fabiano Rosas <farosas@suse.de>
Add the cpr-transfer migration mode, which allows the user to transfer
a guest to a new QEMU instance on the same host with minimal guest pause
time, by preserving guest RAM in place, albeit with new virtual addresses
in new QEMU, and by preserving device file descriptors. Pages that were
locked in memory for DMA in old QEMU remain locked in new QEMU, because the
descriptor of the device that locked them remains open.
cpr-transfer preserves memory and devices descriptors by sending them to
new QEMU over a unix domain socket using SCM_RIGHTS. Such CPR state cannot
be sent over the normal migration channel, because devices and backends
are created prior to reading the channel, so this mode sends CPR state
over a second "cpr" migration channel. New QEMU reads the cpr channel
prior to creating devices or backends. The user specifies the cpr channel
in the channel arguments on the outgoing side, and in a second -incoming
command-line parameter on the incoming side.
The user must start old QEMU with the the '-machine aux-ram-share=on' option,
which allows anonymous memory to be transferred in place to the new process
by transferring a memory descriptor for each ram block. Memory-backend
objects must have the share=on attribute, but memory-backend-epc is not
supported.
The user starts new QEMU on the same host as old QEMU, with command-line
arguments to create the same machine, plus the -incoming option for the
main migration channel, like normal live migration. In addition, the user
adds a second -incoming option with channel type "cpr". This CPR channel
must support file descriptor transfer with SCM_RIGHTS, i.e. it must be a
UNIX domain socket.
To initiate CPR, the user issues a migrate command to old QEMU, adding
a second migration channel of type "cpr" in the channels argument.
Old QEMU stops the VM, saves state to the migration channels, and enters
the postmigrate state. New QEMU mmap's memory descriptors, and execution
resumes.
The implementation splits qmp_migrate into start and finish functions.
Start sends CPR state to new QEMU, which responds by closing the CPR
channel. Old QEMU detects the HUP then calls finish, which connects the
main migration channel.
In summary, the usage is:
qemu-system-$arch -machine aux-ram-share=on ...
start new QEMU with "-incoming <main-uri> -incoming <cpr-channel>"
Issue commands to old QEMU:
migrate_set_parameter mode cpr-transfer
{"execute": "migrate", ...
{"channel-type": "main"...}, {"channel-type": "cpr"...} ... }
Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Acked-by: Markus Armbruster <armbru@redhat.com>
Link: https://lore.kernel.org/r/1736967650-129648-17-git-send-email-steven.sistare@oracle.com
Signed-off-by: Fabiano Rosas <farosas@suse.de>
Add functions to create a QEMUFile based on a unix URI, for saving or
loading, for use by cpr-transfer mode to preserve CPR state.
Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Link: https://lore.kernel.org/r/1736967650-129648-16-git-send-email-steven.sistare@oracle.com
Signed-off-by: Fabiano Rosas <farosas@suse.de>
Define functions to put/get file descriptors to/from a QEMUFile, for qio
channels that support SCM_RIGHTS. Maintain ordering such that
put(A), put(fd), put(B)
followed by
get(A), get(fd), get(B)
always succeeds. Other get orderings may succeed but are not guaranteed.
Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Link: https://lore.kernel.org/r/1736967650-129648-14-git-send-email-steven.sistare@oracle.com
Signed-off-by: Fabiano Rosas <farosas@suse.de>
Extend the -incoming option to allow an @MigrationChannel to be specified.
This allows channels other than 'main' to be described on the command
line, which will be needed for CPR.
Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
Acked-by: Peter Xu <peterx@redhat.com>
Link: https://lore.kernel.org/r/1736967650-129648-13-git-send-email-steven.sistare@oracle.com
Signed-off-by: Fabiano Rosas <farosas@suse.de>
Export migrate_uri_parse for use outside migration internals, and define
a method migrate_is_uri that indicates when migrate_uri_parse should
be used.
Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Link: https://lore.kernel.org/r/1736967650-129648-12-git-send-email-steven.sistare@oracle.com
Signed-off-by: Fabiano Rosas <farosas@suse.de>
CPR must save state that is needed after QEMU is restarted, when devices
are realized. Thus the extra state cannot be saved in the migration
channel, as objects must already exist before that channel can be loaded.
Instead, define auxilliary state structures and vmstate descriptions, not
associated with any registered object, and serialize the aux state to a
cpr-specific channel in cpr_state_save. Deserialize in cpr_state_load
after QEMU restarts, before devices are realized.
Provide accessors for clients to register file descriptors for saving.
The mechanism for passing the fd's to the new process will be specific
to each migration mode, and added in subsequent patches.
Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
Reviewed-by: Fabiano Rosas <farosas@suse.de>
Reviewed-by: Peter Xu <peterx@redhat.com>
Link: https://lore.kernel.org/r/1736967650-129648-8-git-send-email-steven.sistare@oracle.com
Signed-off-by: Fabiano Rosas <farosas@suse.de>
When QPL compression is enabled on the migration channel and the same
dirty page changes from a normal page to a zero page in the iterative
memory copy, the dirty page will not be updated to a zero page again
on the target side, resulting in incorrect memory data on the source
and target sides.
The root cause is that the target side does not record the normal pages
to the receivedmap.
The solution is to add ramblock_recv_bitmap_set_offset in target side
to record the normal pages.
Signed-off-by: Yuan Liu <yuan1.liu@intel.com>
Reviewed-by: Jason Zeng <jason.zeng@intel.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Message-Id: <20241218091413.140396-4-yuan1.liu@intel.com>
Signed-off-by: Fabiano Rosas <farosas@suse.de>
When QPL compression is enabled on the migration channel and the same
dirty page changes from a normal page to a zero page in the iterative
memory copy, the dirty page will not be updated to a zero page again
on the target side, resulting in incorrect memory data on the source
and target sides.
The root cause is that the target side does not record the normal pages
to the receivedmap.
The solution is to add ramblock_recv_bitmap_set_offset in target side
to record the normal pages.
Signed-off-by: Yuan Liu <yuan1.liu@intel.com>
Reviewed-by: Jason Zeng <jason.zeng@intel.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Message-Id: <20241218091413.140396-3-yuan1.liu@intel.com>
Signed-off-by: Fabiano Rosas <farosas@suse.de>
When compression is enabled on the migration channel and
the pages processed are all zero pages, these pages will
not be sent and updated on the target side, resulting in
incorrect memory data on the source and target sides.
The root cause is that all compression methods call
multifd_send_prepare_common to determine whether to compress
dirty pages, but multifd_send_prepare_common does not update
the IOV of MultiFDPacket_t when all dirty pages are zero pages.
The solution is to always update the IOV of MultiFDPacket_t
regardless of whether the dirty pages are all zero pages.
Fixes: 303e6f54f9 ("migration/multifd: Implement zero page transmission on the multifd thread.")
Cc: qemu-stable@nongnu.org #9.0+
Signed-off-by: Yuan Liu <yuan1.liu@intel.com>
Reviewed-by: Jason Zeng <jason.zeng@intel.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Message-Id: <20241218091413.140396-2-yuan1.liu@intel.com>
Signed-off-by: Fabiano Rosas <farosas@suse.de>
Currently, if an array of pointers contains a NULL pointer, that
pointer will be encoded as '0' in the stream. Since the JSON writer
doesn't define a "pointer" type, that '0' will now be an uint8, which
is different from the original type being pointed to, e.g. struct.
(we're further calling uint8 "nullptr", but that's irrelevant to the
issue)
That mixed-type array shouldn't be compressed, otherwise data is lost
as the code currently makes the whole array have the type of the first
element:
css = {NULL, NULL, ..., 0x5555568a7940, NULL};
{"name": "s390_css", "instance_id": 0, "vmsd_name": "s390_css",
"version": 1, "fields": [
...,
{"name": "css", "array_len": 256, "type": "nullptr", "size": 1},
...,
]}
In the above, the valid pointer at position 254 got lost among the
compressed array of nullptr.
While we could disable the array compression when a NULL pointer is
found, the JSON part of the stream still makes part of downtime, so we
should avoid writing unecessary bytes to it.
Keep the array compression in place, but if NULL and non-NULL pointers
are mixed break the array into several type-contiguous pieces :
css = {NULL, NULL, ..., 0x5555568a7940, NULL};
{"name": "s390_css", "instance_id": 0, "vmsd_name": "s390_css",
"version": 1, "fields": [
...,
{"name": "css", "array_len": 254, "type": "nullptr", "size": 1},
{"name": "css", "type": "struct", "struct": {"vmsd_name": "s390_css_img", ... }, "size": 768},
{"name": "css", "type": "nullptr", "size": 1},
...,
]}
Now each type-discontiguous region will become a new JSON entry. The
reader should interpret this as a concatenation of values, all part of
the same field.
Parsing the JSON with analyze-script.py now shows the proper data
being pointed to at the places where the pointer is valid and
"nullptr" where there's NULL:
"s390_css (14)": {
...
"css": [
"nullptr",
"nullptr",
...
"nullptr",
{
"chpids": [
{
"in_use": "0x00",
"type": "0x00",
"is_virtual": "0x00"
},
...
]
},
"nullptr",
}
Reviewed-by: Peter Xu <peterx@redhat.com>
Message-Id: <20250109185249.23952-7-farosas@suse.de>
Signed-off-by: Fabiano Rosas <farosas@suse.de>
QEMU plays a trick with null pointers inside an array of pointers in a VMSD
field. See 07d4e69147 ("migration/vmstate: fix array of ptr with
nullptrs") for more details on why. The idea makes sense in general, but
it may overlooked the JSON writer where it could write nothing in a
"struct" in the JSON hints section.
We hit some analyze-migration.py issues on s390 recently, showing that some
of the struct field contains nothing, like:
{"name": "css", "array_len": 256, "type": "struct", "struct": {}, "size": 1}
As described in details by Fabiano:
https://lore.kernel.org/r/87pll37cin.fsf@suse.de
It could be that we hit some null pointers there, and JSON was gone when
they're null pointers.
To fix it, instead of hacking around only at VMStateInfo level, do that
from VMStateField level, so that JSON writer can also be involved. In this
case, JSON writer will replace the pointer array (which used to be a
"struct") to be the real representation of the nullptr field.
Signed-off-by: Peter Xu <peterx@redhat.com>
Message-Id: <20250109185249.23952-6-farosas@suse.de>
Signed-off-by: Fabiano Rosas <farosas@suse.de>
Rename vmstate_info_nullptr from "uint64_t" to "nullptr". This vmstate
actually reads and writes just a byte, so the proper name would be
uint8. However, since this is a marker for a NULL pointer, it's
convenient to have a more explicit name that can be identified by the
consumers of the JSON part of the stream.
Change the name to "nullptr" and add support for it in the
analyze-migration.py script. Arbitrarily use the name of the type as
the value of the field to avoid the script showing 0x30 or '0', which
could be confusing for readers.
Reviewed-by: Peter Xu <peterx@redhat.com>
Message-Id: <20250109185249.23952-5-farosas@suse.de>
Signed-off-by: Fabiano Rosas <farosas@suse.de>
This patch proposes a flag to maintain disk activation status globally. It
mostly rewrites disk activation mgmt for QEMU, including COLO and QMP
command xen_save_devices_state.
Backgrounds
===========
We have two problems on disk activations, one resolved, one not.
Problem 1: disk activation recover (for switchover interruptions)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
When migration is either cancelled or failed during switchover, especially
when after the disks are inactivated, QEMU needs to remember re-activate
the disks again before vm starts.
It used to be done separately in two paths: one in qmp_migrate_cancel(),
the other one in the failure path of migration_completion().
It used to be fixed in different commits, all over the places in QEMU. So
these are the relevant changes I saw, I'm not sure if it's complete list:
- In 2016, commit fe904ea824 ("migration: regain control of images when
migration fails to complete")
- In 2017, commit 1d2acc3162 ("migration: re-active images while migration
been canceled after inactive them")
- In 2023, commit 6dab4c93ec ("migration: Attempt disk reactivation in
more failure scenarios")
Now since we have a slightly better picture maybe we can unify the
reactivation in a single path.
One side benefit of doing so is, we can move the disk operation outside QMP
command "migrate_cancel". It's possible that in the future we may want to
make "migrate_cancel" be OOB-compatible, while that requires the command
doesn't need BQL in the first place. This will already do that and make
migrate_cancel command lightweight.
Problem 2: disk invalidation on top of invalidated disks
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
This is an unresolved bug for current QEMU. Link in "Resolves:" at the
end. It turns out besides the src switchover phase (problem 1 above), QEMU
also needs to remember block activation on destination.
Consider two continuous migration in a row, where the VM was always paused.
In that scenario, the disks are not activated even until migration
completed in the 1st round. When the 2nd round starts, if QEMU doesn't
know the status of the disks, it needs to try inactivate the disk again.
Here the issue is the block layer API bdrv_inactivate_all() will crash a
QEMU if invoked on already inactive disks for the 2nd migration. For
detail, see the bug link at the end.
Implementation
==============
This patch proposes to maintain disk activation with a global flag, so we
know:
- If we used to inactivate disks for migration, but migration got
cancelled, or failed, QEMU will know it should reactivate the disks.
- On incoming side, if the disks are never activated but then another
migration is triggered, QEMU should be able to tell that inactivate is
not needed for the 2nd migration.
We used to have disk_inactive, but it only solves the 1st issue, not the
2nd. Also, it's done in completely separate paths so it's extremely hard
to follow either how the flag changes, or the duration that the flag is
valid, and when we will reactivate the disks.
Convert the existing disk_inactive flag into that global flag (also invert
its naming), and maintain the disk activation status for the whole
lifecycle of qemu. That includes the incoming QEMU.
Put both of the error cases of source migration (failure, cancelled)
together into migration_iteration_finish(), which will be invoked for
either of the scenario. So from that part QEMU should behave the same as
before. However with such global maintenance on disk activation status, we
not only cleanup quite a few temporary paths that we try to maintain the
disk activation status (e.g. in postcopy code), meanwhile it fixes the
crash for problem 2 in one shot.
For freshly started QEMU, the flag is initialized to TRUE showing that the
QEMU owns the disks by default.
For incoming migrated QEMU, the flag will be initialized to FALSE once and
for all showing that the dest QEMU doesn't own the disks until switchover.
That is guaranteed by the "once" variable.
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2395
Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Fabiano Rosas <farosas@suse.de>
Message-Id: <20241206230838.1111496-7-peterx@redhat.com>
Signed-off-by: Fabiano Rosas <farosas@suse.de>
