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From: Jason Gunthorpe <jgg@ziepe.ca>
To: Oded Gabbay <ogabbay@kernel.org>
Cc: "Christian König" <christian.koenig@amd.com>,
	"Linux-Kernel@Vger. Kernel. Org" <linux-kernel@vger.kernel.org>,
	"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
	"Daniel Vetter" <daniel.vetter@ffwll.ch>,
	"Gal Pressman" <galpress@amazon.com>,
	"Yossi Leybovich" <sleybo@amazon.com>,
	"Maling list - DRI developers" <dri-devel@lists.freedesktop.org>,
	linux-rdma <linux-rdma@vger.kernel.org>,
	"Linux Media Mailing List" <linux-media@vger.kernel.org>,
	"Doug Ledford" <dledford@redhat.com>,
	"Dave Airlie" <airlied@gmail.com>,
	"Alex Deucher" <alexander.deucher@amd.com>,
	"Leon Romanovsky" <leonro@nvidia.com>,
	"Christoph Hellwig" <hch@lst.de>,
	"amd-gfx list" <amd-gfx@lists.freedesktop.org>,
	"moderated list:DMA BUFFER SHARING FRAMEWORK"
	<linaro-mm-sig@lists.linaro.org>,
	"Tomer Tayar" <ttayar@habana.ai>
Subject: Re: [PATCH v6 2/2] habanalabs: add support for dma-buf exporter
Date: Fri, 1 Oct 2021 11:52:09 -0300	[thread overview]
Message-ID: <20211001145209.GP3544071@ziepe.ca> (raw)
In-Reply-To: <CAFCwf110SPfqpjKO7e2W-MSs6iSdecCwS6CwKx4cL-DjqriT2Q@mail.gmail.com>

On Thu, Sep 30, 2021 at 03:46:35PM +0300, Oded Gabbay wrote:

> After reading the kernel iommu code, I think this is not relevant
> here, and I'll add a comment appropriately but I'll also write it
> here, and please correct me if my understanding is wrong.
> 
> The memory behind this specific dma-buf has *always* resided on the
> device itself, i.e. it lives only in the 'device' domain (after all,
> it maps a PCI bar address which points to the device memory).
> Therefore, it was never in the 'CPU' domain and hence, there is no
> need to perform a sync of the memory to the CPU's cache, as it was
> never inside that cache to begin with.
> 
> This is not the same case as with regular memory which is dma-mapped
> and then copied into the device using a dma engine. In that case,
> the memory started in the 'CPU' domain and moved to the 'device'
> domain. When it is unmapped it will indeed be recycled to be used
> for another purpose and therefore we need to sync the CPU cache.
> 
> Is my understanding correct ?

It makes sense to me

Jason

  reply	other threads:[~2021-10-01 14:52 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-12 16:53 [PATCH v6 0/2] Add p2p via dmabuf to habanalabs Oded Gabbay
2021-09-12 16:53 ` [PATCH v6 1/2] habanalabs: define uAPI to export FD for DMA-BUF Oded Gabbay
2021-09-28 17:13   ` Jason Gunthorpe
2021-09-28 19:12     ` Oded Gabbay
2021-09-12 16:53 ` [PATCH v6 2/2] habanalabs: add support for dma-buf exporter Oded Gabbay
2021-09-28 17:36   ` Jason Gunthorpe
2021-09-28 21:17     ` Oded Gabbay
2021-09-30 12:46       ` Oded Gabbay
2021-10-01 14:52         ` Jason Gunthorpe [this message]
2021-10-01 14:50       ` Jason Gunthorpe
2021-09-14 14:18 ` [PATCH v6 0/2] Add p2p via dmabuf to habanalabs Daniel Vetter
2021-09-14 14:58   ` Oded Gabbay
2021-09-14 16:12   ` Jason Gunthorpe
2021-09-15  7:45     ` Oded Gabbay
2021-09-16 12:31       ` Daniel Vetter
2021-09-16 12:44         ` Oded Gabbay
2021-09-16 13:16           ` Oded Gabbay
2021-09-17 12:25           ` Daniel Vetter
2021-09-16 13:10         ` Jason Gunthorpe
2021-09-17 12:30           ` Daniel Vetter
2021-09-18  8:38             ` Oded Gabbay
2021-09-23  9:22               ` Oded Gabbay
2021-09-28  7:04                 ` Oded Gabbay
2021-09-30  9:13                   ` Daniel Vetter

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