Re: [PATCH v4 17/23] iommu/arm-smmu-v3-iommufd: Add vsmmu_alloc impl op

[Nicolin Chen <nicolinc@nvidia.com>]

On Thu, May 15, 2025 at 02:19:02PM -0300, Jason Gunthorpe wrote:
> On Thu, May 08, 2025 at 08:02:38PM -0700, Nicolin Chen wrote:
> > An impl driver might want to allocate its own type of vIOMMU object or the
> > standard IOMMU_VIOMMU_TYPE_ARM_SMMUV3 by setting up its own SW/HW bits, as
> > the tegra241-cmdqv driver will add IOMMU_VIOMMU_TYPE_TEGRA241_CMDQV.
> > 
> > Add a vsmmu_alloc op and prioritize it in arm_vsmmu_alloc().
> > 
> > Reviewed-by: Pranjal Shrivastava <praan@google.com>
> > Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
> > ---
> >  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h     |  6 ++++++
> >  .../iommu/arm/arm-smmu-v3/arm-smmu-v3-iommufd.c | 17 +++++++++++------
> >  2 files changed, 17 insertions(+), 6 deletions(-)
> > 
> > diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
> > index 6b8f0d20dac3..a5835af72417 100644
> > --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
> > +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
> > @@ -16,6 +16,7 @@
> >  #include <linux/sizes.h>
> >  
> >  struct arm_smmu_device;
> > +struct arm_smmu_domain;
> >  
> >  /* MMIO registers */
> >  #define ARM_SMMU_IDR0			0x0
> > @@ -720,6 +721,11 @@ struct arm_smmu_impl_ops {
> >  	int (*init_structures)(struct arm_smmu_device *smmu);
> >  	struct arm_smmu_cmdq *(*get_secondary_cmdq)(
> >  		struct arm_smmu_device *smmu, struct arm_smmu_cmdq_ent *ent);
> > +	struct arm_vsmmu *(*vsmmu_alloc)(
> > +		struct arm_smmu_device *smmu,
> > +		struct arm_smmu_domain *smmu_domain, struct iommufd_ctx *ictx,
> > +		unsigned int viommu_type,
> > +		const struct iommu_user_data *user_data);
> >  };
> 
> I think you should put the supported viommu type here in the ops
> struct and match it here:

OK. A single type per impl might be enough for now, so it can
be a static one.

> > +	/* Prioritize the impl that may support IOMMU_VIOMMU_TYPE_ARM_SMMUV3 */
> > +	if (master->smmu->impl_ops && master->smmu->impl_ops->vsmmu_alloc)
> > +		vsmmu = master->smmu->impl_ops->vsmmu_alloc(
> > +			master->smmu, s2_parent, ictx, viommu_type, user_data);
> 
> instead of the EOPNOTSUPP dance. Either the impl_ops supports the
> requested viommu as an extension or we are running in the normal mode?

I think we can only do normal mode if requested viommu is the
normal SMMUV3 type, i.e. still need to reject a type other than
!CMDQV nor !SMMUV3, right?

> Is there a reason to allocate a different viommu if the userspace does
> not enable the implementation specific features?

Hmm, what is this different viommu?

If VMM doesn't want VCMDQ, it should go with the normal SMMUV3
type.

Thanks
Nicolin