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Re: [Qemu-devel] [PATCH for-2.4 v2 0/2] vhost: check if vhost has capaci


From: Michael S. Tsirkin
Subject: Re: [Qemu-devel] [PATCH for-2.4 v2 0/2] vhost: check if vhost has capacity for hotplugged memory
Date: Thu, 30 Jul 2015 09:25:55 +0300

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" <address@hidden> 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 ...

> > 
> > 
> > > 
> > > 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



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