Messages in this thread | | | Subject | Re: [PATCH 2/4] iommu: Add PASID support for DMA mapping API users | From | Lu Baolu <> | Date | Thu, 9 Dec 2021 10:21:38 +0800 |
| |
On 12/9/21 9:56 AM, Tian, Kevin wrote: >> From: Jacob Pan <jacob.jun.pan@linux.intel.com> >> Sent: Thursday, December 9, 2021 2:50 AM >> >>> Can a device issue DMA requests with PASID even there's no system >> IOMMU >>> or the system IOMMU is disabled? >>> >> Good point. >> If IOMMU is not enabled, device cannot issue DMA requests with PASID. This >> API will not be available. Forgot to add dummy functions to the header. >> > > PASID is a PCI thing, not defined by IOMMU. > > I think the key is physically if IOMMU is disabled, how will root complex > handle a PCI memory request including a PASID TLP prefix? Does it block > such request due to no IOMMU to consume PASID or simply ignore PASID > and continue routing the request to the memory controller? > > If block, then having an iommu interface makes sense. > > If ignore, possibly a DMA API call makes more sense instead, implying that > this extension can be used even when iommu is disabled. > > I think that is what Baolu wants to point out.
Yes, exactly. Imagining in the VM guest environment, do we require a vIOMMU for this functionality? vIOMMU is not performance friendly if we put aside the security considerations.
Best regards, baolu
| |