> -----Original Message-----
> From: Igor Mammedov [mailto:imamm...@redhat.com]
> Sent: Saturday, December 23, 2017 2:49 AM
> To: Zhoujian (jay) <jianjay.z...@huawei.com>
> Cc: qemu-devel@nongnu.org; m...@redhat.com; Huangweidong (C)
> <weidong.hu...@huawei.com>; Gonglei (Arei) <arei.gong...@huawei.com>;
> wangxin (U) <wangxinxin.w...@huawei.com>; Liuzhe (Cloud Open Labs, NFV)
> <gary.liu...@huawei.com>; dgilb...@redhat.com
> Subject: Re: [PATCH v2 2/2] vhost: double check used memslots number
>
> On Fri, 15 Dec 2017 16:45:55 +0800
> Jay Zhou <jianjay.z...@huawei.com> wrote:
>
> > If the VM already has N(N>8) available memory slots for vhost user,
> > the VM will be crashed in vhost_user_set_mem_table if we try to
> > hotplug the first vhost user NIC.
> > This patch checks if memslots number exceeded or not after updating
> > vhost_user_used_memslots.
> Can't understand commit message, pls rephrase (what is being fixed, and
> how it's fixed) also include reproducing steps for crash and maybe
> describe call flow/backtrace that triggers crash.
Sorry about my pool english
>
> PS:
> I wasn't able to reproduce crash
Steps to reproduce:
(1) start up a VM successfully without any vhost device
(2) hotplug 8 DIMM memory successfully
(3) hotplug a vhost-user NIC, the VM crashed, it asserted
at the line
assert(fd_num < VHOST_MEMORY_MAX_NREGIONS);
in vhost_user_set_mem_table()
Regards,
Jay
> >
> > Signed-off-by: Jay Zhou <jianjay.z...@huawei.com>
> > ---
> > hw/virtio/vhost.c | 27 +++++++++++++++++++++++----
> > 1 file changed, 23 insertions(+), 4 deletions(-)
> >
> > diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c index
> > 59a32e9..e45f5e2 100644
> > --- a/hw/virtio/vhost.c
> > +++ b/hw/virtio/vhost.c
> > @@ -1234,6 +1234,18 @@ static void vhost_virtqueue_cleanup(struct
> vhost_virtqueue *vq)
> > event_notifier_cleanup(&vq->masked_notifier);
> > }
> >
> > +static bool vhost_dev_used_memslots_is_exceeded(struct vhost_dev
> > +*hdev) {
> > + if (hdev->vhost_ops->vhost_get_used_memslots() >
> > + hdev->vhost_ops->vhost_backend_memslots_limit(hdev)) {
> > + error_report("vhost backend memory slots limit is less"
> > + " than current number of present memory slots");
> > + return true;
> > + }
> > +
> > + return false;
> > +}
> > +
> > int vhost_dev_init(struct vhost_dev *hdev, void *opaque,
> > VhostBackendType backend_type, uint32_t
> > busyloop_timeout) { @@ -1252,10 +1264,7 @@ int vhost_dev_init(struct
> > vhost_dev *hdev, void *opaque,
> > goto fail;
> > }
> >
> > - if (hdev->vhost_ops->vhost_get_used_memslots() >
> > - hdev->vhost_ops->vhost_backend_memslots_limit(hdev)) {
> > - error_report("vhost backend memory slots limit is less"
> > - " than current number of present memory slots");
> > + if (vhost_dev_used_memslots_is_exceeded(hdev)) {
> why do you keep this check?
> it seems always be false
>
>
>
> > r = -1;
> > goto fail;
> > }
> > @@ -1341,6 +1350,16 @@ int vhost_dev_init(struct vhost_dev *hdev, void
> *opaque,
> > hdev->memory_changed = false;
> > memory_listener_register(&hdev->memory_listener,
> &address_space_memory);
> > QLIST_INSERT_HEAD(&vhost_devices, hdev, entry);
> > +
> > + if (vhost_dev_used_memslots_is_exceeded(hdev)) {
> > + r = -1;
> > + if (busyloop_timeout) {
> > + goto fail_busyloop;
> > + } else {
> > + goto fail;
> > + }
> > + }
> seem to be right thing to do, since after registering listener for the
> first time used_memslots will be updated to actual value.
>
>
> I did some testing and without this hunk/patch
>
> on 'device_add virtio-net-pci,netdev=net0' qemu prints:
>
> qemu-system-x86_64: vhost_set_mem_table failed: Argument list too long (7)
> qemu-system-x86_64: unable to start vhost net: 7: falling back on
> userspace virtio
>
> and network is operational in guest, but with this patch
>
> "netdev_add ...,vhost-on" prints:
>
> vhost backend memory slots limit is less than current number of present
> memory slots vhost-net requested but could not be initialized
>
> and following "device_add virtio-net-pci,netdev=net0" prints:
>
> TUNSETOFFLOAD ioctl() failed: Bad file descriptor TUNSETOFFLOAD ioctl()
> failed: Bad file descriptor
>
> adapter is still hot-plugged but guest networking is broken (can't get IP
> address via DHCP)
>
> so patch seems introduces a regression or something broken elsewhere and
> this exposes issue, not sure what qemu reaction should be in this case
> i.e. when netdev_add fails
> 1: should we fail followed up device_add or
> 2: make it fall back to userspace virtio
>
> I'd go for #2,
> Michael what's your take on it?
>
> > +
> > return 0;
> >
> > fail_busyloop:
