[dpdk-dev] [PATCH 2/2] uio: new driver to support PCI MSI-X

[Vladislav Zolotarov]

On Oct 6, 2015 12:55 AM, "Michael S. Tsirkin" <mst at redhat.com> wrote:
>
> On Thu, Oct 01, 2015 at 11:33:06AM +0300, Michael S. Tsirkin wrote:
> > Just forwarding events is not enough to make a valid driver.
> > What is missing is a way to access the device in a safe way.
>
> Thinking about it some more, maybe some devices don't do DMA, and merely
> signal events with MSI/MSI-X.
>
> The fact you mention igb_uio in the cover letter seems to hint that this
> isn't the case, and that the real intent is to abuse it for DMA-capable
> devices, but still ...
>
> If we assume such a simple device, we need to block userspace from
> tweaking at least the MSI control and the MSI-X table.
> And changing BARs might make someone else corrupt the MSI-X
> table, so we need to block it from changing BARs, too.
>
> Things like device reset will clear the table.  I guess this means we
> need to track access to reset, too, make sure we restore the
> table to a sane config.
>
> PM  capability can be used to reset things tooI think. Better be
> careful about that.
>
> And a bunch of devices could be doing weird things that need
> to be special-cased.
>
> All of this is what VFIO is already dealing with.
>
> Maybe extending VFIO for this usecase, or finding another way to share
> code might be a better idea than duplicating the code within uio?

How about instead of trying to invent the wheel just go and attack the
problem directly just like i've proposed already a few times in the last
days: instead of limiting the UIO limit the users that are allowed to use
UIO to privileged users only (e.g. root). This would solve all clearly
unresolvable issues u are raising here all together, wouldn't it?

>
> --
> MST