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Re: [Qemu-devel] [PATCH v2 2/2] vhost: double check used memslots number
From: |
Michael S. Tsirkin |
Subject: |
Re: [Qemu-devel] [PATCH v2 2/2] vhost: double check used memslots number |
Date: |
Fri, 22 Dec 2017 23:15:09 +0200 |
On Fri, Dec 22, 2017 at 07:48:55PM +0100, Igor Mammedov wrote:
> On Fri, 15 Dec 2017 16:45:55 +0800
> Jay Zhou <address@hidden> 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.
>
> PS:
> I wasn't able to reproduce crash
>
> >
> > Signed-off-by: Jay Zhou <address@hidden>
> > ---
> > 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?
OK but there's a vhost force flag, if that is set we definitely should
fail device_add.
Also, hotplug can follow device_add, should be handled similarly.
> > +
> > return 0;
> >
> > fail_busyloop:
[Qemu-devel] [PATCH v2 2/2] vhost: double check used memslots number, Jay Zhou, 2017/12/15
Re: [Qemu-devel] [PATCH v2 2/2] vhost: double check used memslots number, Zhoujian (jay), 2017/12/23
Re: [Qemu-devel] [PATCH v2 0/2] vhost: two fixes, no-reply, 2017/12/16
Re: [Qemu-devel] [PATCH v2 0/2] vhost: two fixes, Michael S. Tsirkin, 2017/12/19