On Thu, Dec 02, 2021 at 16:56:49 +0100, Jiri Denemark wrote: > Userfaultfd is by default allowed only for privileged processes. Since > libvirt runs QEMU unprivileged, we need to enable unprivileged access to > userfaultfd before starting post-copy migration. > > Rather than providing a static sysctl configuration file, we set the > sysctl knob in runtime once post-copy migration is requested. This way > unprivileged_userfaultfd is only enabled once actually used. > > https://bugzilla.redhat.com/show_bug.cgi?id=1945420 > > Signed-off-by: Jiri Denemark <jdenemar@xxxxxxxxxx> > --- > src/qemu/qemu_migration_params.c | 25 +++++++++++++++++++++++++ > 1 file changed, 25 insertions(+) > > diff --git a/src/qemu/qemu_migration_params.c b/src/qemu/qemu_migration_params.c > index dbc3219826..a9449ed1ff 100644 > --- a/src/qemu/qemu_migration_params.c > +++ b/src/qemu/qemu_migration_params.c > @@ -804,6 +804,24 @@ qemuMigrationCapsToJSON(virBitmap *caps, > } > > > +static void > +qemuMigrationParamsEnableUserfaultfd(virDomainObj *vm) passing 'vm' > +{ > + const char *sysctl = "/proc/sys/vm/unprivileged_userfaultfd"; > + > + if (!virFileExists(sysctl)) > + return; > + > + VIR_DEBUG("Enabling unprivileged userfaultfd for post-copy migration of " > + "domain %s", vm->def->name); Just to debug-log the VM name is a bit pointless. If debug logs are enabled you'll be able to figure out the migrated VM by other log entries. > + > + if (virFileWriteStr(sysctl, "1", 0) < 0) { > + virReportSystemError(errno, "%s", > + _("failed to enable unprivileged userfaultfd")); Reporting an error and not actually failing is also something we rarely do. Firstly it can set the error object and report a spurious error in cases when we'd forget to set an error, and additionally it can flood system logs with 'error' level messages which is also getting frequently reported. > + } > +} > + > + > /** > * qemuMigrationParamsApply > * @driver: qemu driver > @@ -839,6 +857,13 @@ qemuMigrationParamsApply(virQEMUDriver *driver, > goto cleanup; > } > } else { > + /* userfaultfd may only be enabled for privileged processes by default, > + * we need to make sure QEMU can use it before enabling post-copy > + * migration */ > + if (virBitmapIsBitSet(priv->migrationCaps, QEMU_MIGRATION_CAP_POSTCOPY) && > + virBitmapIsBitSet(migParams->caps, QEMU_MIGRATION_CAP_POSTCOPY)) > + qemuMigrationParamsEnableUserfaultfd(vm); > + > if (!(caps = qemuMigrationCapsToJSON(priv->migrationCaps, migParams->caps))) > goto cleanup; > > -- > 2.34.1 >
