On Fri, Mar 03, 2023 at 01:47:53PM -0800, Jacob Pan wrote: > Hi Kevin, > > On Thu, 2 Mar 2023 09:43:03 +0000, "Tian, Kevin" <kevin.tian@xxxxxxxxx> > wrote: > > > > From: Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx> > > > Sent: Thursday, March 2, 2023 9:00 AM > > > > > > Global PASID allocation is under IOMMU SVA code since it is the primary > > > use case. However, some architecture such as VT-d, global PASIDs are > > > necessary for its internal use of DMA API with PASID. > > > > No, global PASID is not a VT-d restriction. It's from ENQCMD/S hence a > > device requirement. > I meant VT-d based platforms, it is kind of intertwined in that ENQCMDS > does not restrict RIDPASID!=DMA PASID, vt-d does. Without this > restriction, there wouldn't be a need for this patch. Let me reword. No, Kevin is right, there is nothing about VT-d that needs global PASID values. The driver should be managing RID2PASID itself to avoid conflicting with any in-use PASID, either by changing RID2PASID on demand or by setting it to a value that is not part of the PASID number space, eg we can make 0 entirely invalid, or the driver can reduce max_pasid of the devices it controls and use PASID_MAX. Jason
