Re: [PATCH v2 0/2] spapr: Use vIOMMU translation for virtio by default

[David Gibson]

On Thu, Feb 13, 2020 at 12:46:43PM +0100, Greg Kurz wrote:
> On Thu, 13 Feb 2020 11:58:35 +1100
> David Gibson <address@hidden> wrote:
> 
> > Upcoming Secure VM support for pSeries machines introduces some
> > complications for virtio, since the transfer buffers need to be
> > explicitly shared so that the hypervisor can access them.
> > 
> > While it's not strictly speaking dependent on it, the fact that virtio
> > devices bypass normal platform IOMMU translation complicates the issue
> > on the guest side.  Since there are some significan downsides to
> > bypassing the vIOMMU anyway, let's just disable that.
> > 
> > There's already a flag to do this in virtio, just turn it on by
> > default for forthcoming pseries machine types.
> > 
> > Any opinions on whether dropping support for the older guest kernels
> > is acceptable at this point?
> > 
> 
> As expected, this breaks compatibility with existing RHEL 6.10 guests. Each
> patch in this series requires an extra -global option to be specified on
> the command line in order to boot successfully.
> 
> Patch 1: -global virtio-pci.disable-legacy=auto
> Patch 2: -global virtio-pci.iommu_platform=off

Right, or setting an older machine type.

> As seen on the RH site [1], RHEL6 will reach "End of Maintenance Support
> or Maintenance Support 2 (Product retirement)" on November 30, 2020 and
> "End of Extended Life-cycle Support" on June 30, 2024.
> 
> Not sure if it's okay to drop support for RHEL6 this soon.

Hm, yeah.  I'm happy enough to do this upstream, downstream will
require some discussion.

> RHEL 7.7 guests seem to be unaffected.

Yeah, I already checked and RHEL7 has backported support for modern
virtio and the iommu platform flag.

> 
> [1] https://access.redhat.com/support/policy/updates/errata/#Life_Cycle_Dates
> 
> > Changes since v1:
> >  * Added information on which guest kernel versions will no longer
> >    work with these changes
> >  * Use Michael Tsirkin's suggested better way of handling the machine
> >    type change
> > 
> > David Gibson (2):
> >   spapr: Disable legacy virtio devices for pseries-5.0 and later
> >   spapr: Enable virtio iommu_platform=on by default
> > 
> >  hw/ppc/spapr.c | 16 +++++++++++++++-
> >  1 file changed, 15 insertions(+), 1 deletion(-)
> > 
> 

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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