* Adalbert Lazăr (ala...@bitdefender.com) wrote: > On Mon, 27 Apr 2020 20:08:55 +0100, "Dr. David Alan Gilbert" > <dgilb...@redhat.com> wrote: > > * Adalbert Lazăr (ala...@bitdefender.com) wrote: > > > From: Marian Rotariu <marian.c.rota...@gmail.com> > > > > > > It is possible that the introspection tool has made some changes inside > > > the introspected VM which can make the guest crash if the introspection > > > connection is suddenly closed. > > > > > > When the live migration starts, for now, the introspection tool is > > > signaled to remove its hooks from the introspected VM. > > > > > > CC: Juan Quintela <quint...@redhat.com> > > > CC: "Dr. David Alan Gilbert" <dgilb...@redhat.com> > > > Signed-off-by: Marian Rotariu <marian.c.rota...@gmail.com> > > > Signed-off-by: Adalbert Lazăr <ala...@bitdefender.com> > > > > OK, so this isn't too intrusive to the migration code; and other than > > renaming 'start_live_migration_thread' to > > 'start_outgoing_migration_thread' I think I'd be OK with this, > > > > but it might depend what your overall aim is. > > > > For example, you might be better intercepting each migration_state > > change in your notifier, that's much finer grain than just the start of > > migration. > > Thank you, Dave. > > We want to intercept the live migration and 'block' it while the guest > is running (some changes made to the guest by the introspection app has > to be undone while the vCPUs are in certain states). > > I'm not sure what is the best way to block these kind of events > (including the pause/shutdown commands). If calling main_loop_wait() > is enough (patch [22/26] kvm: vmi: add 'async_unhook' property [1]) > then we can drop a lot of code. > > The use of a notifier will be nice, but from what I understand, we can't > block the migration from a notification callback.
Oh, if your intention is *just* to block a migration starting then you can use 'migrate_add_blocker' - see hw/9pfs/9p.c for an example where it's used and then removed; they use it to stop migration while the fs is mounted. That causes an attempt to start a migration to give an error (of your choosing). > > The other thing I worry about is that there doesn't seem to be much > > guard against odd orderings of things - for example, what happens > > if the introspection client was to issue the INTERCEPT_MIGRATE command > > twice while a migration was already running? Or before an actual > > incoming channel connetion had happened? > > > > Dave > > Sorry that I haven't described the interception. When we intercept > an action that we want to 'block', we set a static variable first, > regardless if the introspection channel is connected or not, and : > > - if the introspection channel is not connected we don't block the > action, but this (variable) will prevent the activation of this > channel until the action (ie. migrate) is completed (a). I assume > that there could be only one migrate (or suspend/pause) user command > at any given time (b). > > - if the introspection channel is connected, the introspection app > is signaled to start its unhook/undo process. We let the code flow > continue, but the action (migrate/suspend/pause) is delayed until > the introspection channel is closed. Meanwhile, any other intercepted > action will not be blocked/delayed (c), but the fact that these actions > are in progress is saved to static variables and the introspecton > channel won't be reactivated. > > Indeed, there are cases that are not handled well: > > a) if the migration is started and canceled before the introspection > object is created (through QMP), the introspection channel will be > disabled until the next migration starts and finishes. > > b) if a migration command has been delayed, a following migrate command > (if this is possible) won't be delayed and we will have two migration > threads started. > > c) if a migration command has been delayed, a following suspend/pause > command won't be delayed and the introspection app might not have > enough time to finish its unhook/undo process. Yeh that sounds a bit messy. Dave > [1]: > https://lore.kernel.org/qemu-devel/20200415005938.23895-23-ala...@bitdefender.com/ > > > > --- > > > accel/kvm/vmi.c | 31 +++++++++++++++++++++++++++---- > > > include/sysemu/vmi-intercept.h | 1 + > > > migration/migration.c | 18 +++++++++++++++--- > > > migration/migration.h | 2 ++ > > > 4 files changed, 45 insertions(+), 7 deletions(-) > > > > > > diff --git a/accel/kvm/vmi.c b/accel/kvm/vmi.c > > > index 90906478b4..ea7191e48d 100644 > > > --- a/accel/kvm/vmi.c > > > +++ b/accel/kvm/vmi.c > > > @@ -21,6 +21,8 @@ > > > #include "chardev/char.h" > > > #include "chardev/char-fe.h" > > > #include "migration/vmstate.h" > > > +#include "migration/migration.h" > > > +#include "migration/misc.h" > > > > > > #include "sysemu/vmi-intercept.h" > > > #include "sysemu/vmi-handshake.h" > > > @@ -58,6 +60,7 @@ typedef struct VMIntrospection { > > > int64_t vm_start_time; > > > > > > Notifier machine_ready; > > > + Notifier migration_state_change; > > > bool created_from_command_line; > > > > > > bool kvmi_hooked; > > > @@ -74,9 +77,11 @@ static const char *action_string[] = { > > > "suspend", > > > "resume", > > > "force-reset", > > > + "migrate", > > > }; > > > > > > static bool suspend_pending; > > > +static bool migrate_pending; > > > > > > #define TYPE_VM_INTROSPECTION "introspection" > > > > > > @@ -88,6 +93,15 @@ static bool suspend_pending; > > > static Error *vm_introspection_init(VMIntrospection *i); > > > static void vm_introspection_reset(void *opaque); > > > > > > +static void migration_state_notifier(Notifier *notifier, void *data) > > > +{ > > > + MigrationState *s = data; > > > + > > > + if (migration_has_failed(s)) { > > > + migrate_pending = false; > > > + } > > > +} > > > + > > > static void machine_ready(Notifier *notifier, void *data) > > > { > > > VMIntrospection *i = container_of(notifier, VMIntrospection, > > > machine_ready); > > > @@ -144,6 +158,9 @@ static void complete(UserCreatable *uc, Error **errp) > > > > > > ic->uniq = i; > > > > > > + i->migration_state_change.notify = migration_state_notifier; > > > + add_migration_state_change_notifier(&i->migration_state_change); > > > + > > > qemu_register_reset(vm_introspection_reset, i); > > > } > > > > > > @@ -478,6 +495,9 @@ static void > > > continue_with_the_intercepted_action(VMIntrospection *i) > > > case VMI_INTERCEPT_SUSPEND: > > > vm_stop(RUN_STATE_PAUSED); > > > break; > > > + case VMI_INTERCEPT_MIGRATE: > > > + start_live_migration_thread(migrate_get_current()); > > > + break; > > > default: > > > error_report("VMI: %s: unexpected action %d", > > > __func__, i->intercepted_action); > > > @@ -571,9 +591,9 @@ static void chr_event_open(VMIntrospection *i) > > > { > > > Error *local_err = NULL; > > > > > > - if (suspend_pending) { > > > - info_report("VMI: %s: too soon (suspend=%d)", > > > - __func__, suspend_pending); > > > + if (suspend_pending || migrate_pending) { > > > + info_report("VMI: %s: too soon (suspend=%d, migrate=%d)", > > > + __func__, suspend_pending, migrate_pending); > > > maybe_disable_socket_reconnect(i); > > > qemu_chr_fe_disconnect(&i->sock); > > > return; > > > @@ -608,7 +628,7 @@ static void chr_event_close(VMIntrospection *i) > > > cancel_unhook_timer(i); > > > cancel_handshake_timer(i); > > > > > > - if (suspend_pending) { > > > + if (suspend_pending || migrate_pending) { > > > maybe_disable_socket_reconnect(i); > > > > > > if (i->intercepted_action != VMI_INTERCEPT_NONE) { > > > @@ -680,6 +700,9 @@ static bool > > > record_intercept_action(VMI_intercept_command action) > > > break; > > > case VMI_INTERCEPT_FORCE_RESET: > > > break; > > > + case VMI_INTERCEPT_MIGRATE: > > > + migrate_pending = true; > > > + break; > > > default: > > > return false; > > > } > > > diff --git a/include/sysemu/vmi-intercept.h > > > b/include/sysemu/vmi-intercept.h > > > index ef591b49e7..b4a9a3faa7 100644 > > > --- a/include/sysemu/vmi-intercept.h > > > +++ b/include/sysemu/vmi-intercept.h > > > @@ -15,6 +15,7 @@ typedef enum { > > > VMI_INTERCEPT_SUSPEND, > > > VMI_INTERCEPT_RESUME, > > > VMI_INTERCEPT_FORCE_RESET, > > > + VMI_INTERCEPT_MIGRATE, > > > } VMI_intercept_command; > > > > > > bool vm_introspection_intercept(VMI_intercept_command ic, Error **errp); > > > diff --git a/migration/migration.c b/migration/migration.c > > > index 187ac0410c..222037d739 100644 > > > --- a/migration/migration.c > > > +++ b/migration/migration.c > > > @@ -55,6 +55,8 @@ > > > #include "qemu/queue.h" > > > #include "multifd.h" > > > > > > +#include "sysemu/vmi-intercept.h" > > > + > > > #define MAX_THROTTLE (32 << 20) /* Migration transfer speed > > > throttling */ > > > > > > /* Amount of time to allocate to each "chunk" of bandwidth-throttled > > > @@ -3471,6 +3473,13 @@ static void *migration_thread(void *opaque) > > > return NULL; > > > } > > > > > > +void start_live_migration_thread(MigrationState *s) > > > +{ > > > + qemu_thread_create(&s->thread, "live_migration", migration_thread, s, > > > + QEMU_THREAD_JOINABLE); > > > + s->migration_thread_running = true; > > > +} > > > + > > > void migrate_fd_connect(MigrationState *s, Error *error_in) > > > { > > > Error *local_err = NULL; > > > @@ -3534,9 +3543,12 @@ void migrate_fd_connect(MigrationState *s, Error > > > *error_in) > > > migrate_fd_cleanup(s); > > > return; > > > } > > > - qemu_thread_create(&s->thread, "live_migration", migration_thread, s, > > > - QEMU_THREAD_JOINABLE); > > > - s->migration_thread_running = true; > > > + > > > + if (vm_introspection_intercept(VMI_INTERCEPT_MIGRATE, &error_in)) { > > > + return; > > > + } > > > + > > > + start_live_migration_thread(s); > > > } > > > > > > void migration_global_dump(Monitor *mon) > > > diff --git a/migration/migration.h b/migration/migration.h > > > index 507284e563..eb5668e1f2 100644 > > > --- a/migration/migration.h > > > +++ b/migration/migration.h > > > @@ -263,6 +263,8 @@ struct MigrationState > > > uint8_t clear_bitmap_shift; > > > }; > > > > > > +void start_live_migration_thread(MigrationState *s); > > > + > > > void migrate_set_state(int *state, int old_state, int new_state); > > > > > > void migration_fd_process_incoming(QEMUFile *f, Error **errp); > > > > > -- > > Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK > > > -- Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
