Re: [RFC PATCH v3 1/2] iommu: Add capability IOMMU_CAP_VIOMMU

[Lu Baolu]

Hi Leon,

On 2021/1/16 16:39, Leon Romanovsky wrote:
> On Sat, Jan 16, 2021 at 09:20:16AM +0800, Lu Baolu wrote:
> > Hi,
> >
> > On 2021/1/15 14:31, Leon Romanovsky wrote:
> > > On Fri, Jan 15, 2021 at 07:49:47AM +0800, Lu Baolu wrote:
> > > > Hi Leon,
> > > >
> > > > On 1/14/21 9:26 PM, Leon Romanovsky wrote:
> > > > > On Thu, Jan 14, 2021 at 09:30:02AM +0800, Lu Baolu wrote:
> > > > > > Some vendor IOMMU drivers are able to declare that it is running in a VM
> > > > > > context. This is very valuable for the features that only want to be
> > > > > > supported on bare metal. Add a capability bit so that it could be used.
> > > > >
> > > > > And how is it used? Who and how will set it?
> > > >
> > > > Use the existing iommu_capable(). I should add more descriptions about
> > > > who and how to use it.
> > >
> > > I want to see the code that sets this capability.
> >
> > Currently we have Intel VT-d and the virt-iommu setting this capability.
> >
> >   static bool intel_iommu_capable(enum iommu_cap cap)
> >   {
> >   	if (cap == IOMMU_CAP_CACHE_COHERENCY)
> >   		return domain_update_iommu_snooping(NULL) == 1;
> >   	if (cap == IOMMU_CAP_INTR_REMAP)
> >   		return irq_remapping_enabled == 1;
> > +	if (cap == IOMMU_CAP_VIOMMU)
> > +		return caching_mode_enabled();
> >
> >   	return false;
> >   }
> >
> > And,
> >
> > +static bool viommu_capable(enum iommu_cap cap)
> > +{
> > +	if (cap == IOMMU_CAP_VIOMMU)
> > +		return true;
> > +
> > +	return false;
> > +}
>
> These two functions are reading this cap and not setting.
> Where can I see code that does "cap = IOMMU_CAP_VIOMMU" and not "=="?

The iommu_capable() is a generic IOMMU interface to query IOMMU
capabilities. It takes @bus and @cap as input, and calls the callback
of vendor iommu. If the vendor iommu driver supports the specific
capability, it returns true. Otherwise, it returns false.

bool iommu_capable(struct bus_type *bus, enum iommu_cap cap)
{
        if (!bus->iommu_ops || !bus->iommu_ops->capable)
                return false;

        return bus->iommu_ops->capable(cap);
}
EXPORT_SYMBOL_GPL(iommu_capable);

In the vendor iommu's callback, it checks the capability and returns a
value according to its capability, just as showed above.

Best regards,
baolu