Re: [Xen-devel] Upstream Dom0 DRM problems regarding swiotlb

[Michael Labriola <michael.d.labriola@xxxxxxxxx>]

On Wed, Feb 13, 2019 at 11:09 AM Jan Beulich <JBeulich@xxxxxxxx> wrote:
>
> >>> On 13.02.19 at 17:00, <michael.d.labriola@xxxxxxxxx> wrote:
> > On Wed, Feb 13, 2019 at 9:28 AM Jan Beulich <JBeulich@xxxxxxxx> wrote:
> >> >>> On 13.02.19 at 15:10, <michael.d.labriola@xxxxxxxxx> wrote:
> >> > Ah, so this isn't necessarily Xen-specific but rather any paravirtual
> >> > guest?  That hadn't crossed my mind.  Is there an easy way to find out
> >> > if we're a pv guest in the need_swiotlb conditionals?
> >>
> >> There's xen_pv_domain(), but I think xen_swiotlb would be more to
> >> the point if the check is already to be Xen-specific. There's no generic
> >> "is PV" predicate that I'm aware of.
> >
> > Well, that makes doing conditional code right more difficult.  I
> > assume since there isn't a generic predicate, and PV isn't new, that
> > it's absence is by design?  To reign in the temptation to sprinkle
> > conditional code all over the kernel?  ;-)
>
> Well, with lguest gone, Xen is the only PV environment the kernel
> can run in, afaik at least. I guess to decide between the suggested
> options or the need for some abstracting macro (or yet something
> else), you'll really need to ask the driver maintainers. Or simply
> send a patch their way implementing one of them, and see what
> their reaction is.

Thanks, I'll do that.

When you said any PV guest would need swiotlb, not just Xen, does that
mean anything that's using CONFIG_PARAVIRT?  That appears to include
KVM, VMware, Xen PVH, and Xen HVM in addition to Xen PV, all of which
populate the global pv_info structure at kernel bootup.  Is Xen PV the
only one of those that requires swiotlb?

-Mike

-- 
Michael D Labriola
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