On Thu, 30 Jul 2015 10:58:23 +0300 "Michael S. Tsirkin" <m...@redhat.com> wrote:
> On Thu, Jul 30, 2015 at 09:31:34AM +0200, Igor Mammedov wrote: > > On Thu, 30 Jul 2015 09:29:56 +0300 > > "Michael S. Tsirkin" <m...@redhat.com> wrote: > > > > > On Thu, Jul 30, 2015 at 09:25:55AM +0300, Michael S. Tsirkin wrote: > > > > On Thu, Jul 30, 2015 at 08:22:18AM +0200, Igor Mammedov wrote: > > > > > On Wed, 29 Jul 2015 18:03:36 +0300 > > > > > "Michael S. Tsirkin" <m...@redhat.com> wrote: > > > > > > > > > > > On Wed, Jul 29, 2015 at 01:49:47PM +0200, Igor Mammedov wrote: > > > > > > > v1->v2: > > > > > > > * replace probbing with checking for > > > > > > > /sys/module/vhost/parameters/max_mem_regions and > > > > > > > if it's missing has non wrong value return > > > > > > > hardcoded legacy limit (64 slots). > > > > > > > > > > > > > > it's defensive patchset which helps to avoid QEMU crashing > > > > > > > at memory hotplug time by checking that vhost has free capacity > > > > > > > for an additional memory slot. > > > > > > > > > > > > What if vhost is added after memory hotplug? Don't you need > > > > > > to check that as well? > > > > > vhost device can be hotplugged after memory hotplug as far as > > > > > current slots count doesn't exceed its limit, > > > > > if limit is exceeded device_add would fail or virtio device > > > > > would fallback to non vhost mode at its start-up (depends on > > > > > how particular device treats vhost_start failure). > > > > > > > > Where exactly does it fail? > > > > memory_listener_register returns void so clearly it's not that ... > > > > > > Oh, dev_start fails. But that's not called at device_add time. > > > And vhost-user can't fall back to anything. > > Yes, looks like it would lead to non functional vhost-user backed device > > since there isn't any error handling at that stage. > > > > But it's would be the same without memory hotplug also, one just has to > > start QEMU with several -name memdev=xxx options to cause that condition. > > Absolutely. And kvm has this problem too if using kernels before 2014. > > But I have a question: do we have to figure the number of > chunks exactly? How about being blunt, and just limiting the > number of memory devices? it would be guess work, number of chunks is not static and changes during guest runtime as it configures devices so chunks # at startup != chunks # at any other time > > How about this: > - teach memory listeners about a new "max mem devices" field # of mem devices != # of memory ranges > - when registering a listener, check that # of mem devices > does not exceed this limit, if not - fail registering > listener > - when adding mem device, check no existing listener > has a limit that conflicts with it > > Of course we could add a separate linked list+ register API with just this > field instead of adding it to a memory listener, if that seems > more appropriate. > > > > Probably the best place to add this check is at vhost_net_init() > > so that backend creation fails when one tries to add it on monitor/CLI > > I'd say vhost_dev_init - it's not network specific at all. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Igor Mammedov (2): > > > > > > > vhost: add vhost_has_free_slot() interface > > > > > > > pc-dimm: add vhost slots limit check before commiting to hotplug > > > > > > > > > > > > > > hw/mem/pc-dimm.c | 7 +++++++ > > > > > > > hw/virtio/vhost-backend.c | 21 ++++++++++++++++++++- > > > > > > > hw/virtio/vhost-user.c | 8 +++++++- > > > > > > > hw/virtio/vhost.c | 21 +++++++++++++++++++++ > > > > > > > include/hw/virtio/vhost-backend.h | 2 ++ > > > > > > > include/hw/virtio/vhost.h | 1 + > > > > > > > stubs/Makefile.objs | 1 + > > > > > > > stubs/vhost.c | 6 ++++++ > > > > > > > 8 files changed, 65 insertions(+), 2 deletions(-) > > > > > > > create mode 100644 stubs/vhost.c > > > > > > > > > > > > > > -- > > > > > > > 1.8.3.1 > > > >
