Re: [PATCH v2] vfio: do not coalesce DMA mappings

[David Marchand <david.marchand@redhat.com>]

Hello Anatoly,

On Wed, Apr 5, 2023 at 4:17 PM Burakov, Anatoly
<anatoly.burakov@intel.com> wrote:
> >> Could you please provide some steps to reproduce the hotplug issue
> >> you're having? It would be great to have a test case for this patchset
> >> to put it in context.
> >
> > I am working on CDX bus
> > (http://patchwork.dpdk.org/project/dpdk/patch/20230124140746.594066-2-nipun.gupta@amd.com/) and trying out some cases for plug/unplug.
> >
> > The test is as follows:
> >    # Run testpmd application
> >    ./dpdk-testpmd -c 0x3 -- -i --nb-cores=1
> >
> >    # Bind to VFIO
> >    echo "vfio-cdx" >  /sys/bus/cdx/devices/cdx-00\:00/driver_override
> >    echo "cdx-00:00" > /sys/bus/cdx/drivers_probe
> >
> >    # Plug a device
> >    testpmd> port attach cdx:cdx-00:00
> >
> >    #quit testpmd
> >    testpmd> quit
> >
> > This gave error at testpmd exit that memory cannot be freed. On
> > debugging I updated this code and seems it should be seen with any of
> > the device.
> >
> > I see similar test case (without quit) mentioned
> > https://doc.dpdk.org/dts/test_plans/hotplug_test_plan.html, but the
> > difference is that it is with igb_uio and issue is being observed with
> > VFIO.
> >
> > Please note the device/bus mentioned in the commands is not yet
> > upstreamed in DPDK, but patches would be sent out soon.
> >
> > Thanks,
> > Nipun
> >
>
> Thanks, I can reproduce this issue with regular devices too (run testpmd
> with no devices, bind a NIC to VFIO, attach it, then quit). You're
> correct in that since the initial mapping was done with mapping large
> contiguous zones (such as when mempools are created before attach), any
> subsequent freeing of memory will cause these errors to happen.
>
> I don't think this can be fixed by anything other than not doing the
> contiguous mapping thing, so provisionally, I think this patch should be
> accepted. I'll play around with it some more and get back to you :)

Can we conclude on this topic?
It is best we merge this kind of change the sooner possible for a release.

Thanks.


-- 
David Marchand