On Tue, 6 Dec 2016 17:31:11 +0100
Joerg Roedel <j...@8bytes.org> wrote:
> Hi Jacob,
>
> On Thu, Dec 01, 2016 at 01:50:26PM -0800, Jacob Pan wrote:
> > diff --git a/drivers/iommu/intel-iommu.c
> > b/drivers/iommu/intel-iommu.c index 27596e6..f112aa9 100644
> > --- a/drivers/iommu/intel-iommu.c
> > +++ b/drivers/iommu/intel-iommu.c
> > @@ -5173,6 +5173,29 @@ static void intel_iommu_remove_device(struct
> > device *dev) }
> >
> > #ifdef CONFIG_INTEL_IOMMU_SVM
> > +#define MAX_NR_PASID_BITS (20)
> > +static inline unsigned long intel_iommu_get_pts(struct intel_iommu
> > *iommu) +{
> > + unsigned long pts;
> > +
> > + /*
> > + * Convert ecap_pss to extend context entry pts encoding,
> > also
> > + * respect the soft pasid_max value set by the iommu.
> > + * - number of PASID bits = ecap_pss + 1
> > + * - number of PASID table entries = 2^(pts + 5)
> > + * Therefore, pts = ecap_pss - 4
> > + * e.g. KBL ecap_pss = 0x13, PASID has 20 bits, pts = 15
> > + */
> > + if (ecap_pss(iommu->ecap) < 5)
> > + return 0;
> > +
> > + pts = (ecap_pss(iommu->ecap) - 4);
> > +
> > + /* pasid_max is encoded as actual number of entries not
> > the bits */
> > + return min(find_first_bit((unsigned long
> > *)&iommu->pasid_max,
> > + MAX_NR_PASID_BITS) - 5,
> > pts);
>
> Iommu->max_pasid already depends on ecap_pss(), so I think it is
> better to just calculate the pts value as ffs(iommu->max_pasid) - 5.
> This way you don't need an extra function and have a simpler
> calculation.
>
Good point. I will make the change. Still keeping the lower bond
sanity check to prevent insanely small pss.
I initially did the patch w/o knowing David's pasid_max patch in rc7.
I was under the impression that pasid_max is a temp solution until we
remove the requirement of contiguous memory allocation.
Thanks,
Jacob
