Re: [virtio-comment] [PATCH 5/5] virtio-pci: implement VIRTIO_F_QUEUE_STATE

["Zhu, Lingshan" <lingshan.zhu@intel.com>]

On 9/13/2023 12:19 PM, Parav Pandit wrote:
> > From: Zhu, Lingshan <lingshan.zhu@intel.com>
> > Sent: Wednesday, September 13, 2023 9:44 AM
> >
> >
> > On 9/12/2023 9:35 PM, Parav Pandit wrote:
> > > > From: Zhu, Lingshan <lingshan.zhu@intel.com>
> > > > Sent: Tuesday, September 12, 2023 6:39 PM
> > > >
> > > > On 9/12/2023 6:41 PM, Parav Pandit wrote:
> > > > > > From: Zhu, Lingshan <lingshan.zhu@intel.com>
> > > > > > Sent: Tuesday, September 12, 2023 4:05 PM I mean, why do you think
> > > > > > my series can not work with P2P
> > > > > Because it misses the intermediate mode STOP that we have in series [1].
> > > > >
> > > > > [1]
> > > > > https://lists.oasis-open.org/archives/virtio-comment/202309/msg00071
> > > > > .h
> > > > > tml
> > > > Again, when SUSPEND:
> > > > 1) the device freezes, means stop operation in both data-path and
> > > > control-path, except the device status
> > > Exactly, including the RESET_VQ command also cannot be served because
> > device is frozen.
> > see below
> > > > 2) a new feature bit will be introduced in V2, to allow RESET_VQ
> > > > after SUSPEND
> > > RESET_VQ after suspend is simply wrong. Because device is already
> > suspended to not respond to some  extra RESET_VQ command.
> > No, when the device presents SUSPEND, that means the device config space is
> > stabilized at that moment, from the SW perspective the device will not make
> > changes to config space until !SUSPEND.
> >
> > However at that moment, the driver can still make modification to the config
> > space and the driver handles the synchronization(checks, re-read, etc), so the
> > driver is responsible for what it reads.
> It should be named as SUSPEND_CFG_SPACE.!
> All of this frankly seems intrusive enough as Michael pointed out.
> Good luck.
it also SUSPEND the data-path
>   
> > As you can see, this is not perfect, so SiWei suggest to implement a new feature
> > bit to control this, and it will be implemented in V2.
> > > > 3) if there is a device doing P2P against the device.
> > > > They should be pass-through-ed to the same guest and should be
> > > > suspended as well for LM, or it is a security problem.
> > > There is no security problem. Multiple passthrough devices and P2P is already
> > there in PCI using ACS for probably a decade now.
> > As you aware of ACS, that means you have to trust them all, for example P2P
> > devices has to be placed in one IOMMU group, and all devices in the group
> > should be pass-through-ed to a guest
> Such things are done by the hypervisor already. There is nothing virtio specific here.
> There is no security problem.
> If there is one, please file CVE for generic P2P in the pci-sig and we will handle them this Thu meeting.