Re: [Xen-devel] [PATCH v4 10/12] IOMMU: introduce IOMMU_MIXED config option

[Julien Grall <julien.grall@xxxxxxx>]

Hi Jan,

On 06/11/2018 15:48, Jan Beulich wrote:
> > > > On 02.10.18 at 12:38, <julien.grall@xxxxxxx> wrote:
> > On 02/10/2018 11:18, Jan Beulich wrote:
> > > ARM is intended to gain support for heterogeneous IOMMUs on a single
> > > system. This not only disallows boot time replacement of respective
> > > indirect calls (handling of which is the main goal of the introduction
> > > here), but more generally disallows calls using the iommu_ops() return
> > > value directly - all such calls need to have means (commonly a domain
> > > pointer) to know the targeted IOMMU.
> > >
> > > Disallow all hooks lacking such context for the time being, which in
> > > effect is some dead code elimination for ARM. Once extended suitably,
> > > individual of these hooks can be moved out of their guards again in the
> > > future.
> > While in theory it is possible to have platform with hetereneous IOMMUs.
> >    I don't see such such support coming in Xen for the foreseeable
> > future. Note that even Linux does not support such case.
> >
> > This patch is going to make more complicate to unshare page-tables as
> > now we would need to care of mixed case. So I would rather not set
> > IOMMU_MIXED on Arm until we have a use case for it.
> So if I drop this here, how would you want iommu_get_ops()
> get handled on Arm (patch 11)? Right now I'd mean to leave it
> alone, but it could also be switched to the (new) x86 way (but
> that would then perhaps make mixed mode introduction more
> difficult down the road), allowing to get away with fewer
> #ifdef-s.
I would introduce the iommu_get_ops for x86 in asm-x86/iommu.h.

Cheers,

--
Julien Grall

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