Re: [Xen-devel] [PATCH V2 6/6] iommu/arm: Add Renesas IPMMU-VMSA support

[Oleksandr <olekstysh@xxxxxxxxx>]

On 14.08.19 20:38, Julien Grall wrote:
> Hi Oleksandr,
Hi Julien.


> On 02/08/2019 17:39, Oleksandr Tyshchenko wrote:
> > +static int ipmmu_iommu_domain_init(struct domain *d)
> > +{
> > +    struct ipmmu_vmsa_xen_domain *xen_domain;
> > +
> > +    xen_domain = xzalloc(struct ipmmu_vmsa_xen_domain);
> > +    if ( !xen_domain )
> > +        return -ENOMEM;
> > +
> > +    spin_lock_init(&xen_domain->lock);
> > +    INIT_LIST_HEAD(&xen_domain->cache_domains);
> > +    /*
> > +     * We don't create Root IPMMU domain here, it will be created on 
> > demand
> > +     * only, when attaching the first master device to this Xen 
> > domain in
> > +     * ipmmu_assign_device().
> > +     * xen_domain->root_domain = NULL;
> > +    */
> > +
> > +    dom_iommu(d)->arch.priv = xen_domain;
> While looking at other part of Xen I realized you don't set 
> IOMMU_FEAT_COHERENT_WALK. Does it mean the IOMMU walker does not 
> support coherent walk (i.e snooping the cache)?
*AFAIK*, not supported.

Linux driver reports coherent_walk is not supported as well.


> Note that when this feature is not set, the p2m code will require to 
> clean each P2M entry when updated. So if the IPMMU supports coherent 
> walk, I would strongly suggest to set the flag :).
When playing with non-shared IOMMU in Xen (two years ago), I noticed 
that I had forgotten to use clean_dcache after updating a page table 
entry. I could face faults when
shattering superpages for example. Once I added it, the faults went away 
completely.
So, leave IOMMU_FEAT_COHERENT_WALK in disabled state, but will keep your 
suggestion in mind.

> Cheers,
--
Regards,

Oleksandr Tyshchenko


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