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

[Lu Baolu]

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.

> > Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> > ---
> >   drivers/iommu/intel/iommu.c  | 20 ++++++++++++++++++++
> >   drivers/iommu/virtio-iommu.c |  9 +++++++++
> >   include/linux/iommu.h        |  1 +
> >   3 files changed, 30 insertions(+)
> >
> > diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> > index cb205a04fe4c..8eb022d0e8aa 100644
> > --- a/drivers/iommu/intel/iommu.c
> > +++ b/drivers/iommu/intel/iommu.c
> > @@ -5738,12 +5738,32 @@ static inline bool nested_mode_support(void)
> >   	return ret;
> >   }
> >
> > +static inline bool caching_mode_enabled(void)
> > +{
>
> Kernel coding style is not in favour of inline functions in *.c files.

Yes, agreed.

Best regards,
baolu

> > +	struct dmar_drhd_unit *drhd;
> > +	struct intel_iommu *iommu;
> > +	bool ret = false;
> > +
> > +	rcu_read_lock();
> > +	for_each_active_iommu(iommu, drhd) {
> > +		if (cap_caching_mode(iommu->cap)) {
> > +			ret = true;
> > +			break;
> > +		}
> > +	}
> > +	rcu_read_unlock();
> > +
> > +	return ret;
> > +}
> > +
> >   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;
> >   }
> > diff --git a/drivers/iommu/virtio-iommu.c b/drivers/iommu/virtio-iommu.c
> > index 2bfdd5734844..719793e103db 100644
> > --- a/drivers/iommu/virtio-iommu.c
> > +++ b/drivers/iommu/virtio-iommu.c
> > @@ -931,7 +931,16 @@ static int viommu_of_xlate(struct device *dev, struct of_phandle_args *args)
> >   	return iommu_fwspec_add_ids(dev, args->args, 1);
> >   }
> >
> > +static bool viommu_capable(enum iommu_cap cap)
> > +{
> > +	if (cap == IOMMU_CAP_VIOMMU)
> > +		return true;
> > +
> > +	return false;
> > +}
> > +
> >   static struct iommu_ops viommu_ops = {
> > +	.capable		= viommu_capable,
> >   	.domain_alloc		= viommu_domain_alloc,
> >   	.domain_free		= viommu_domain_free,
> >   	.attach_dev		= viommu_attach_dev,
> > diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> > index b95a6f8db6ff..1d24be667a03 100644
> > --- a/include/linux/iommu.h
> > +++ b/include/linux/iommu.h
> > @@ -94,6 +94,7 @@ enum iommu_cap {
> >   					   transactions */
> >   	IOMMU_CAP_INTR_REMAP,		/* IOMMU supports interrupt isolation */
> >   	IOMMU_CAP_NOEXEC,		/* IOMMU_NOEXEC flag */
> > +	IOMMU_CAP_VIOMMU,		/* IOMMU can declar running in a VM */
> >   };
> >
> >   /*
> > --
> > 2.25.1