lkml.org 
[lkml]   [2019]   [Mar]   [25]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [RFC PATCH] virtio_ring: Use DMA API if guest memory is encrypted
On Sat, Mar 23, 2019 at 05:01:35PM -0400, Michael S. Tsirkin wrote:
> On Thu, Mar 21, 2019 at 09:05:04PM -0300, Thiago Jung Bauermann wrote:
> > Michael S. Tsirkin <mst@redhat.com> writes:
[snip]
> > >> > Is there any justification to doing that beyond someone putting
> > >> > out slow code in the past?
> > >>
> > >> The definition of the ACCESS_PLATFORM flag is generic and captures the
> > >> notion of memory access restrictions for the device. Unfortunately, on
> > >> powerpc pSeries guests it also implies that the IOMMU is turned on
> > >
> > > IIUC that's really because on pSeries IOMMU is *always* turned on.
> > > Platform has no way to say what you want it to say
> > > which is bypass the iommu for the specific device.
> >
> > Yes, that's correct. pSeries guests running on KVM are in a gray area
> > where theoretically they use an IOMMU but in practice KVM ignores it.
> > It's unfortunate but it's the reality on the ground today. :-/

Um.. I'm not sure what you mean by this. As far as I'm concerned
there is always a guest-visible (paravirtualized) IOMMU, and that will
be backed onto the host IOMMU when necessary.

[Actually there is an IOMMU bypass hack that's used by the guest
firmware, but I don't think we want to expose that]

> Well it's not just the reality, virt setups need something that
> emulated IOMMUs don't provide. That is not uncommon, e.g.
> intel's VTD has a "cache mode" field which AFAIK is only used for virt.

--
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
[unhandled content-type:application/pgp-signature]
\
 
 \ /
  Last update: 2019-03-25 05:35    [W:0.120 / U:1.740 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site