Re: [PATCH V10 03/11] iommu/vt-d: Add a helper function to skip agaw

[Jacob Pan]

On Sun, 29 Mar 2020 15:20:55 +0800
Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx> wrote:

> On 2020/3/27 19:53, Tian, Kevin wrote:
> >> From: Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx>
> >> Sent: Saturday, March 21, 2020 7:28 AM
> >>
> >> Signed-off-by: Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx>  
> > 
> > could you elaborate in which scenario this helper function is
> > required?  
> 
> I added below commit message:
> 
>      An Intel iommu domain uses 5-level page table by default. If the
>      iommu that the domain tries to attach supports less page levels,
>      the top level page tables should be skipped. Add a helper to do
>      this so that it could be used in other places.
> 
Thanks Baolu,
I will also add this to my v11, it might save you some time :)


> Best regards,
> baolu
> 
> >     
> >> ---
> >>   drivers/iommu/intel-pasid.c | 22 ++++++++++++++++++++++
> >>   1 file changed, 22 insertions(+)
> >>
> >> diff --git a/drivers/iommu/intel-pasid.c
> >> b/drivers/iommu/intel-pasid.c index 22b30f10b396..191508c7c03e
> >> 100644 --- a/drivers/iommu/intel-pasid.c
> >> +++ b/drivers/iommu/intel-pasid.c
> >> @@ -500,6 +500,28 @@ int intel_pasid_setup_first_level(struct
> >> intel_iommu *iommu,
> >>   }
> >>
> >>   /*
> >> + * Skip top levels of page tables for iommu which has less agaw
> >> + * than default. Unnecessary for PT mode.
> >> + */
> >> +static inline int iommu_skip_agaw(struct dmar_domain *domain,
> >> +				  struct intel_iommu *iommu,
> >> +				  struct dma_pte **pgd)
> >> +{
> >> +	int agaw;
> >> +
> >> +	for (agaw = domain->agaw; agaw > iommu->agaw; agaw--) {
> >> +		*pgd = phys_to_virt(dma_pte_addr(*pgd));
> >> +		if (!dma_pte_present(*pgd)) {
> >> +			return -EINVAL;
> >> +		}
> >> +	}
> >> +	pr_debug_ratelimited("%s: pgd: %llx, agaw %d d_agaw %d\n",
> >> __func__, (u64)*pgd,
> >> +		iommu->agaw, domain->agaw);
> >> +
> >> +	return agaw;
> >> +}
> >> +
> >> +/*
> >>    * Set up the scalable mode pasid entry for second only
> >> translation type. */
> >>   int intel_pasid_setup_second_level(struct intel_iommu *iommu,
> >> --
> >> 2.7.4  
> >   

[Jacob Pan]