Messages in this thread | | | Date | Thu, 30 Sep 2021 08:21:21 -0700 | From | Jacob Pan <> | Subject | Re: [RFC 0/7] Support in-kernel DMA with PASID and SVA |
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Hi Mike,
On Thu, 30 Sep 2021 14:22:34 +0000, "Campin, Mike" <mike.campin@intel.com> wrote:
> I need support for mixed user PASID, kernel PASID and non-PASID use cases > in the driver. > This specific RFC is for kernel PASID only. User PASID native use is supported under SVA lib kernel API and /dev/uacce UAPI or driver specific char dev. Guest PASID is being developed under the new /dev/iommu framework. Non-PASID kernel use should be under DMA API unchanged from the driver's POV. In fact, this proposal will map non-PASID and PASID DMA identically.
Thanks,
Jacob
> -----Original Message----- > From: Jason Gunthorpe <jgg@nvidia.com> > Sent: Wednesday, September 29, 2021 4:43 PM > To: Jacob Pan <jacob.jun.pan@linux.intel.com> > Cc: iommu@lists.linux-foundation.org; LKML > <linux-kernel@vger.kernel.org>; Joerg Roedel <joro@8bytes.org>; Christoph > Hellwig <hch@infradead.org>; Tian, Kevin <kevin.tian@intel.com>; Luck, > Tony <tony.luck@intel.com>; Jiang, Dave <dave.jiang@intel.com>; Raj, > Ashok <ashok.raj@intel.com>; Kumar, Sanjay K <sanjay.k.kumar@intel.com>; > Campin, Mike <mike.campin@intel.com>; Thomas Gleixner > <tglx@linutronix.de> Subject: Re: [RFC 0/7] Support in-kernel DMA with > PASID and SVA > > On Wed, Sep 29, 2021 at 03:57:20PM -0700, Jacob Pan wrote: > > Hi Jason, > > > > On Wed, 29 Sep 2021 16:39:53 -0300, Jason Gunthorpe <jgg@nvidia.com> > > wrote: > > > On Wed, Sep 29, 2021 at 12:37:19PM -0700, Jacob Pan wrote: > > > > > > > For #2, it seems we can store the kernel PASID in struct device. > > > > This will preserve the DMA API interface while making it PASID > > > > capable. Essentially, each PASID capable device would have two > > > > special global > > > > PASIDs: > > > > - PASID 0 for DMA request w/o PASID, aka RID2PASID > > > > - PASID 1 (randomly selected) for in-kernel DMA request w/ > > > > PASID > > > > > > This seems reasonable, I had the same thought. Basically just have > > > the driver issue some trivial call: > > > pci_enable_pasid_dma(pdev, &pasid) > > That would work, but I guess it needs to be an iommu_ call instead of > > pci_? > > Which ever makes sense.. The API should take in a struct pci_device and > return a PCI PASID - at least as a wrapper around a more generic immu api. > > > I think your suggestion is more precise, in case the driver does not > > want to do DMA w/ PASID, we can do less IOTLB flush (PASID 0 only). > > Since it is odd, and it may create overhead, I would do it only when > asked to do it > > > > Having multiple RID's pointing at the same IO page table is > > > something we expect iommufd to require so the whole thing should > > > ideally fall out naturally. > > > That would be the equivalent of attaching multiple devices to the same > > IOMMU domain. right? > > Effectively.. > > Jason
Thanks,
Jacob
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