Re: [PATCH v3 4/7] iommu/vt-d: Reserve RID_PASID from global PASID space

[Jacob Pan]

Hi Baolu,

On Sat, 1 Apr 2023 21:43:13 +0800, Baolu Lu <baolu.lu@xxxxxxxxxxxxxxx>
wrote:

> On 2023/4/1 7:11, Jacob Pan wrote:
> > On VT-d platforms, RID_PASID is used for DMA request without PASID. We
> > should not treat RID_PASID special instead let it be allocated from the
> > global PASID number space. Non-zero value can be used in RID_PASID on
> > Intel VT-d.
> > 
> > For ARM, AMD and others that _always_ use 0 as RID_PASID, there is no
> > impact in that SVA PASID allocation base is 1.
> > 
> > With this change, devices do both DMA with PASID and SVA will not worry
> > about conflicts when it comes to allocating PASIDs for in-kernel DMA.
> > 
> > Signed-off-by: Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx>
> > ---
> >   drivers/iommu/intel/iommu.c | 4 ++++
> >   1 file changed, 4 insertions(+)
> > 
> > diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> > index 9f737ef55463..cbb2670f88ca 100644
> > --- a/drivers/iommu/intel/iommu.c
> > +++ b/drivers/iommu/intel/iommu.c
> > @@ -3956,6 +3956,10 @@ int __init intel_iommu_init(void)
> >   
> >   	intel_iommu_enabled = 1;
> >   
> > +	/* Reserved RID_PASID from the global namespace for legacy DMA
> > */
> > +	WARN_ON(iommu_alloc_global_pasid(PASID_RID2PASID,
> > PASID_RID2PASID) !=
> > +		PASID_RID2PASID);  
> 
> This looks odd. With the previous patch unchanged,
> iommu_alloc_global_pasid() will always return IOMMU_PASID_INVALID if
> CONFIG_IOMMU_SVA is not set.
right, will move out of CONFIG_IOMMU_SVA. good point!

Thanks,

Jacob