Re: [PATCH 1/1] iommu/vt-d: Support asynchronous IOMMU nested capabilities

[Lu Baolu]

Hi Kevin,

On 5/12/21 4:30 PM, Tian, Kevin wrote:
> > From: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> > Sent: Wednesday, May 12, 2021 3:04 PM
> >
> > Current VT-d implementation supports nested translation only if all
> > underlying IOMMUs support the nested capability. This is unnecessary
> > as the upper layer is allowed to create different containers and set
> > them with different type of iommu backend. The IOMMU driver needs to
> > guarantee that devices attached to a nested mode iommu_domain should
> > support nested capabilility.
>
> so the consistency check is now applied only to the IOMMUs that are
> spanned by a given iommu_domain?

Yes.

> > Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> > ---
> >   drivers/iommu/intel/iommu.c | 21 +++++++++++++++++++--
> >   1 file changed, 19 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> > index f1742da42478..1cd4840e6f9f 100644
> > --- a/drivers/iommu/intel/iommu.c
> > +++ b/drivers/iommu/intel/iommu.c
> > @@ -4755,6 +4755,13 @@ static int prepare_domain_attach_device(struct
> > iommu_domain *domain,
> >   	if (!iommu)
> >   		return -ENODEV;
> >
> > +	if ((dmar_domain->flags & DOMAIN_FLAG_NESTING_MODE) &&
> > +	    !ecap_nest(iommu->ecap)) {
> > +		dev_err(dev, "%s: iommu not support nested translation\n",
> > +			iommu->name);
> > +		return -EINVAL;
> > +	}
> > +
> >   	/* check if this iommu agaw is sufficient for max mapped address */
> >   	addr_width = agaw_to_width(iommu->agaw);
> >   	if (addr_width > cap_mgaw(iommu->cap))
> > @@ -5451,11 +5458,21 @@ static int
> >   intel_iommu_enable_nesting(struct iommu_domain *domain)
> >   {
> >   	struct dmar_domain *dmar_domain = to_dmar_domain(domain);
> > +	struct dmar_drhd_unit *drhd;
> > +	struct intel_iommu *iommu;
> > +	bool has_nesting = false;
> >   	unsigned long flags;
> > -	int ret = -ENODEV;
> > +	int ret = -EINVAL;
> > +
> > +	for_each_active_iommu(iommu, drhd)
> > +		if (ecap_nest(iommu->ecap))
> > +			has_nesting = true;
> > +
> > +	if (!has_nesting)
> > +		return -ENODEV;
>
> Isn't above still doing global consistency check?

The logic is if nested mode is globally unsupported, return false.

> >   	spin_lock_irqsave(&device_domain_lock, flags);
> > -	if (nested_mode_support() && list_empty(&dmar_domain->devices))
> > {
> > +	if (list_empty(&dmar_domain->devices)) {
> >   		dmar_domain->flags |= DOMAIN_FLAG_NESTING_MODE;
> >   		dmar_domain->flags &= ~DOMAIN_FLAG_USE_FIRST_LEVEL;
> >   		ret = 0;
> > --
> > 2.25.1

Best regards,
baolu