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Subject: Re: [virtio-dev] Re: [PATCH 0/5] virtio: introduce SUSPEND bit and vq state
On 9/20/2023 8:05 PM, Michael S. Tsirkin wrote:
On Wed, Sep 20, 2023 at 07:22:32PM +0800, Zhu, Lingshan wrote:On 9/20/2023 6:36 PM, Michael S. Tsirkin wrote:On Wed, Sep 20, 2023 at 02:06:13PM +0800, Zhu, Lingshan wrote:On 9/19/2023 2:49 AM, Michael S. Tsirkin wrote:On Mon, Sep 18, 2023 at 06:41:55PM +0000, Parav Pandit wrote:Please refer to the code for setting FEATURES_OK.It wont work when one needs to suspend the device. There is no point of doing such work over registers as fundamental framework is over the AQ.Well not really. It's over admin commands. When these were built the intent always was that it's possible to use admin commands through another interface, other than admin queue. Is there a problem implementing admin commands over a memory BAR? For example, I can see an "admin command" capability pointing at a BAR where commands are supplied, and using a new group type referring to device itself.I am not sure, if a bar cap would be implemented as a proxy for the admin vq based live migration.Not a proxy for a vq in that there's no vq then.I think if the driver sends admin commands through a VF's bar, then VF forwards the admin commands to the PF, it acts like a proxy, or an agent. Anyway it takes admin commands.Why send them to the PF? They are controlling the VF anyway.
I think its still too heavy compared to this series proposal
So the problems we have discussed still exist.then the problems of admin vq LM that we have discussed still exist.I freely admit the finer points of this extended flamewar have been lost on me, and I wager I'm not the only one. I thought you wanted to migrate the device just by accessing the device itself (e.g. the VF) without accessing other devices (e.g. the PF), while Parav wants it in a separate device so the whole of the device itself can passed through to guest. Isn't this, fundamentally, the issue?we are implementing basic facilities for live migration. We have pointed out lots of issues, there are many discussions with Jason and Parav about the problems in migration by admin vq, for example: security, QOS and nested./me shrugs Thanks for the summary I guess. Same applies to almost any proposal. What would help make progress is an explanation why this has grown into a megathread. Do you understand Parav's thoughts well enough to summarize them?
as far as I see, I don't see admin vq as must for live migration. and it does not serve nested for sure.
the bar is only a proxy, doesn't fix anything. and even larger side channel attacking surface: vf-->pf-->vfIn this model there's no pf. BAR belongs to vf itself and you submit commands for the VF through its BAR. Just separate from the pci config space.If using the bar to process admin commands, is this solution too heavy compared to my proposal in this series?somewhat - because it's more comprehensive - you can actually migrate a device using it. this series just begins to define how to poke at some of the vq state - it's a subset of the necessary functionality. And it will give you a bunch of side benefits, such as support for legacy compat commands that were merged.
next version will include in-flight descriptors and dirty page tracking. I failed to process the comments for legacy. legacy devices are defined by code than the spec, if wants to migrate legacy devices, maybe working on QEMU first
The whole attacking surface discussion is also puzzling. We either are or are not discussing confidential computing/TDI. I couldn't figure it out. This needs a separate thread I think.I agree confidential computing is out of spec. Parva mentioned TDISP and even in TDISP spec, it explicitly defined some attacking model, and PF is an example. It is out of spec anyway.OK so we are ignoring TDISP applications for now? Everyone agrees on that?
sure
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