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From: Jason Gunthorpe <jgg@nvidia.com>
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>,
	Tony Luck <tony.luck@intel.com>,
	Dave Jiang <dave.jiang@intel.com>,
	Raj Ashok <ashok.raj@intel.com>,
	"Kumar, Sanjay K" <sanjay.k.kumar@intel.com>,
	mike.campin@intel.com, Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [RFC 0/7] Support in-kernel DMA with PASID and SVA
Date: Wed, 29 Sep 2021 20:43:01 -0300	[thread overview]
Message-ID: <20210929234301.GC964074@nvidia.com> (raw)
In-Reply-To: <20210929155720.794b6e65@jacob-builder>

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

WARNING: multiple messages have this Message-ID (diff)
From: Jason Gunthorpe via iommu <iommu@lists.linux-foundation.org>
To: Jacob Pan <jacob.jun.pan@linux.intel.com>
Cc: "Tian, Kevin" <kevin.tian@intel.com>,
	Tony Luck <tony.luck@intel.com>,
	Dave Jiang <dave.jiang@intel.com>,
	Raj Ashok <ashok.raj@intel.com>,
	"Kumar, Sanjay K" <sanjay.k.kumar@intel.com>,
	LKML <linux-kernel@vger.kernel.org>,
	Christoph Hellwig <hch@infradead.org>,
	iommu@lists.linux-foundation.org, mike.campin@intel.com,
	Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [RFC 0/7] Support in-kernel DMA with PASID and SVA
Date: Wed, 29 Sep 2021 20:43:01 -0300	[thread overview]
Message-ID: <20210929234301.GC964074@nvidia.com> (raw)
In-Reply-To: <20210929155720.794b6e65@jacob-builder>

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
_______________________________________________
iommu mailing list
iommu@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/iommu

  reply	other threads:[~2021-09-29 23:43 UTC|newest]

Thread overview: 58+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-21 20:29 [RFC 0/7] Support in-kernel DMA with PASID and SVA Jacob Pan
2021-09-21 20:29 ` Jacob Pan
2021-09-21 20:29 ` [RFC 1/7] ioasid: reserve special PASID for in-kernel DMA Jacob Pan
2021-09-21 20:29   ` Jacob Pan
2021-09-21 20:29 ` [RFC 2/7] dma-iommu: Add API for DMA request with PASID Jacob Pan
2021-09-21 20:29   ` Jacob Pan
2021-09-21 20:29 ` [RFC 3/7] iommu/vt-d: Add DMA w/ PASID support for PA and IOVA Jacob Pan
2021-09-21 20:29   ` Jacob Pan
2021-09-21 20:29 ` [RFC 4/7] dma-iommu: Add support for DMA w/ PASID in KVA Jacob Pan
2021-09-21 20:29   ` Jacob Pan
2021-09-21 20:29 ` [RFC 5/7] iommu/vt-d: Add support for KVA PASID mode Jacob Pan
2021-09-21 20:29   ` Jacob Pan
2021-09-21 20:29 ` [RFC 6/7] iommu: Add KVA map API Jacob Pan
2021-09-21 20:29   ` Jacob Pan
2021-09-21 20:29 ` [RFC 7/7] dma/idxd: Use dma-iommu PASID API instead of SVA lib Jacob Pan
2021-09-21 20:29   ` Jacob Pan
2021-09-22 17:04 ` [RFC 0/7] Support in-kernel DMA with PASID and SVA Jason Gunthorpe
2021-09-22 17:04   ` Jason Gunthorpe via iommu
2021-09-29 19:37 ` Jacob Pan
2021-09-29 19:37   ` Jacob Pan
2021-09-29 19:39   ` Jason Gunthorpe
2021-09-29 19:39     ` Jason Gunthorpe via iommu
2021-09-29 22:57     ` Jacob Pan
2021-09-29 22:57       ` Jacob Pan
2021-09-29 23:43       ` Jason Gunthorpe [this message]
2021-09-29 23:43         ` Jason Gunthorpe via iommu
2021-09-30 14:22         ` Campin, Mike
2021-09-30 14:22           ` Campin, Mike
2021-09-30 15:21           ` Jacob Pan
2021-09-30 15:21             ` Jacob Pan
2021-10-01 12:24 ` Barry Song
2021-10-01 12:24   ` Barry Song
2021-10-01 12:36   ` Jason Gunthorpe
2021-10-01 12:36     ` Jason Gunthorpe via iommu
2021-10-01 12:45     ` Barry Song
2021-10-01 12:45       ` Barry Song
2021-10-04 16:40       ` Jacob Pan
2021-10-04 16:40         ` Jacob Pan
2021-10-04 18:21         ` Jason Gunthorpe
2021-10-04 18:21           ` Jason Gunthorpe via iommu
2021-10-07  5:43           ` Barry Song
2021-10-07  5:43             ` Barry Song
2021-10-07 11:32             ` Jason Gunthorpe
2021-10-07 11:32               ` Jason Gunthorpe via iommu
2021-10-07 11:54               ` Barry Song
2021-10-07 11:54                 ` Barry Song
2021-10-07 11:59                 ` Jason Gunthorpe
2021-10-07 11:59                   ` Jason Gunthorpe via iommu
2021-10-07 17:50                   ` Jacob Pan
2021-10-07 17:50                     ` Jacob Pan
2021-10-07 17:48                     ` Jason Gunthorpe
2021-10-07 17:48                       ` Jason Gunthorpe via iommu
2021-10-07 18:08                       ` Jacob Pan
2021-10-07 18:08                         ` Jacob Pan
2021-10-07 19:11             ` Jacob Pan
2021-10-07 19:11               ` Jacob Pan
2021-10-07 19:10               ` Jason Gunthorpe
2021-10-07 19:10                 ` Jason Gunthorpe via iommu

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