From: Jason Gunthorpe via iommu <iommu@lists.linux-foundation.org>
To: Barry Song <21cnbao@gmail.com>
Cc: "Tian, Kevin" <kevin.tian@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, Tony Luck <tony.luck@intel.com>,
mike.campin@intel.com
Subject: Re: [RFC 0/7] Support in-kernel DMA with PASID and SVA
Date: Fri, 1 Oct 2021 09:36:23 -0300 [thread overview]
Message-ID: <20211001123623.GM964074@nvidia.com> (raw)
In-Reply-To: <CAGsJ_4z=2y2nVStXP-aAPnQrJJbMmv78mjaMwNc9P9Ec+gCtGw@mail.gmail.com>
On Sat, Oct 02, 2021 at 01:24:54AM +1300, Barry Song wrote:
> I assume KVA mode can avoid this iotlb flush as the device is using
> the page table of the kernel and sharing the whole kernel space. But
> will users be glad to accept this mode?
You can avoid the lock be identity mapping the physical address space
of the kernel and maping map/unmap a NOP.
KVA is just a different way to achive this identity map with slightly
different security properties than the normal way, but it doesn't
reach to the same security level as proper map/unmap.
I'm not sure anyone who cares about DMA security would see value in
the slight difference between KVA and a normal identity map.
> which have been mapped in the current dma-map/unmap with IOMMU backend.
> some drivers are using bouncing buffer to overcome the performance loss of
> dma_map/unmap as copying is faster than unmapping:
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=907676b130711fd1f
It is pretty unforuntate that drivers are hard coding behaviors based
on assumptions of what the portable API is doing under the covers.
Jason
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next prev parent reply other threads:[~2021-10-01 12:36 UTC|newest]
Thread overview: 29+ 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 ` [RFC 1/7] ioasid: reserve special PASID for in-kernel DMA 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 ` [RFC 3/7] iommu/vt-d: Add DMA w/ PASID support for PA and IOVA 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 ` [RFC 5/7] iommu/vt-d: Add support for KVA PASID mode Jacob Pan
2021-09-21 20:29 ` [RFC 6/7] iommu: Add KVA map API Jacob Pan
2021-09-21 20:29 ` [RFC 7/7] dma/idxd: Use dma-iommu PASID API instead of SVA lib Jacob Pan
2021-09-22 17:04 ` [RFC 0/7] Support in-kernel DMA with PASID and SVA Jason Gunthorpe via iommu
2021-09-29 19:37 ` Jacob Pan
2021-09-29 19:39 ` Jason Gunthorpe via iommu
2021-09-29 22:57 ` Jacob Pan
2021-09-29 23:43 ` Jason Gunthorpe via iommu
2021-09-30 14:22 ` Campin, Mike
2021-09-30 15:21 ` Jacob Pan
2021-10-01 12:24 ` Barry Song
2021-10-01 12:36 ` Jason Gunthorpe via iommu [this message]
2021-10-01 12:45 ` Barry Song
2021-10-04 16:40 ` Jacob Pan
2021-10-04 18:21 ` Jason Gunthorpe via iommu
2021-10-07 5:43 ` Barry Song
2021-10-07 11:32 ` Jason Gunthorpe via iommu
2021-10-07 11:54 ` Barry Song
2021-10-07 11:59 ` Jason Gunthorpe via iommu
2021-10-07 17:50 ` Jacob Pan
2021-10-07 17:48 ` Jason Gunthorpe via iommu
2021-10-07 18:08 ` Jacob Pan
2021-10-07 19:11 ` Jacob Pan
2021-10-07 19:10 ` Jason Gunthorpe via iommu
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