RE: [PATCH v2 2/3] iommu/vt-d: Check FL and SL capability sanity in scalable mode

[Tian, Kevin]

> From: Tian, Kevin
> Sent: Monday, September 27, 2021 9:12 AM
> 
> > From: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> > Sent: Sunday, September 26, 2021 7:46 PM
> >
> > An iommu domain could be allocated and mapped before it's attached to
> > any
> > device. This requires that in scalable mode, when the domain is allocated,
> > the format (FL or SL) of the page table must be determined. In order to
> > achieve this, the platform should support consistent SL or FL capabilities
> > on all IOMMU's. This adds a check for this and aborts IOMMU probing if it
> > doesn't meet this requirement.
> 
> Is this a must? Looks the requirement comes from how the current code
> is implemented. It sets DOMAIN_FLAG_USE_FIRST_LEVEL flag in
> alloc_domain. But actually the pgtable is not allocated until the 1st device
> is attached. If this understanding is correct, you can also postpone the flag
> setting until pgtable is actually allocated.

Baolu explained to me that RMRR regions are mapped before device
attach. So this check is necessary

> 
> of course how to handle inconsistent IOMMU capabilities is another
> orthogonal problem. Addressing it should not be only applied to SL/FL
> difference. especially this patch doesn't check consistency. it just
> checks that an IOMMU must support either SL or FL which doesn't
> match the commit msg here.

and the overall inconsistency check mechanism is already in place. 
and the logic here just extends it to cover SL/FL. Given that,

Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>


> 
> >
> > Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> > ---
> >  drivers/iommu/intel/cap_audit.h |  1 +
> >  drivers/iommu/intel/cap_audit.c | 13 +++++++++++++
> >  2 files changed, 14 insertions(+)
> >
> > diff --git a/drivers/iommu/intel/cap_audit.h
> > b/drivers/iommu/intel/cap_audit.h
> > index 74cfccae0e81..d07b75938961 100644
> > --- a/drivers/iommu/intel/cap_audit.h
> > +++ b/drivers/iommu/intel/cap_audit.h
> > @@ -111,6 +111,7 @@ bool intel_cap_smts_sanity(void);
> >  bool intel_cap_pasid_sanity(void);
> >  bool intel_cap_nest_sanity(void);
> >  bool intel_cap_flts_sanity(void);
> > +bool intel_cap_slts_sanity(void);
> >
> >  static inline bool scalable_mode_support(void)
> >  {
> > diff --git a/drivers/iommu/intel/cap_audit.c
> > b/drivers/iommu/intel/cap_audit.c
> > index b12e421a2f1a..040e4ae0e42b 100644
> > --- a/drivers/iommu/intel/cap_audit.c
> > +++ b/drivers/iommu/intel/cap_audit.c
> > @@ -163,6 +163,14 @@ static int cap_audit_static(struct intel_iommu
> > *iommu, enum cap_audit_type type)
> >  			check_irq_capabilities(iommu, i);
> >  	}
> >
> > +	/*
> > +	 * If the system is sane to support scalable mode, either SL or FL
> > +	 * should be sane.
> > +	 */
> > +	if (intel_cap_smts_sanity() &&
> > +	    !intel_cap_flts_sanity() && !intel_cap_slts_sanity())
> > +		return -EFAULT;
> > +
> >  out:
> >  	rcu_read_unlock();
> >  	return 0;
> > @@ -203,3 +211,8 @@ bool intel_cap_flts_sanity(void)
> >  {
> >  	return ecap_flts(intel_iommu_ecap_sanity);
> >  }
> > +
> > +bool intel_cap_slts_sanity(void)
> > +{
> > +	return ecap_slts(intel_iommu_ecap_sanity);
> > +}
> > --
> > 2.25.1