From: Christoph Hellwig <hch@infradead.org>
To: Jason Gunthorpe <jgg@nvidia.com>
Cc: "Christoph Hellwig" <hch@infradead.org>,
"Christian König" <christian.koenig@amd.com>,
"Alex Williamson" <alex.williamson@redhat.com>,
"Cornelia Huck" <cohuck@redhat.com>,
dri-devel@lists.freedesktop.org, kvm@vger.kernel.org,
linaro-mm-sig@lists.linaro.org, linux-media@vger.kernel.org,
"Sumit Semwal" <sumit.semwal@linaro.org>,
"Daniel Vetter" <daniel.vetter@ffwll.ch>,
"Leon Romanovsky" <leon@kernel.org>,
linux-rdma@vger.kernel.org, "Maor Gottlieb" <maorg@nvidia.com>,
"Oded Gabbay" <ogabbay@kernel.org>,
"Dan Williams" <dan.j.williams@intel.com>
Subject: Re: [PATCH v2 4/4] vfio/pci: Allow MMIO regions to be exported through dma-buf
Date: Wed, 7 Sep 2022 08:32:23 -0700 [thread overview]
Message-ID: <Yxi5h09JAzIo4Kh8@infradead.org> (raw)
In-Reply-To: <Yxi3cFfs0SA4XWJw@nvidia.com>
On Wed, Sep 07, 2022 at 12:23:28PM -0300, Jason Gunthorpe wrote:
> 2) DMABUF abuses dma_map_resource() for P2P and thus doesn't work in
> certain special cases.
Not just certain special cases, but one of the main use cases.
Basically P2P can happen in two ways:
a) through a PCIe switch, or
b) through connected root ports
The open code version here only supports a), only supports it when there
is no offset between the 'phyiscal' address of the BAR seen PCIe
endpoint and the Linux way. x86 usually (always?) doesn't have an
offset there, but other architectures often do.
Last but not least I don't really see how the code would even work
when an IOMMU is used, as dma_map_resource will return an IOVA that
is only understood by the IOMMU itself, and not the other endpoint.
How was this code even tested?
next prev parent reply other threads:[~2022-09-07 15:32 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-31 23:12 [PATCH v2 0/4] Allow MMIO regions to be exported through dma-buf Jason Gunthorpe
2022-08-31 23:12 ` [PATCH v2 1/4] dma-buf: Add dma_buf_try_get() Jason Gunthorpe
2022-09-01 7:55 ` Christian König
2022-09-06 16:44 ` Jason Gunthorpe
2022-09-06 17:52 ` Christian König
2022-08-31 23:12 ` [PATCH v2 2/4] vfio: Add vfio_device_get() Jason Gunthorpe
2022-08-31 23:12 ` [PATCH v2 3/4] vfio_pci: Do not open code pci_try_reset_function() Jason Gunthorpe
2022-08-31 23:12 ` [PATCH v2 4/4] vfio/pci: Allow MMIO regions to be exported through dma-buf Jason Gunthorpe
2022-09-06 9:51 ` Christoph Hellwig
2022-09-06 10:38 ` Christian König
2022-09-06 11:48 ` Jason Gunthorpe
2022-09-06 12:34 ` Oded Gabbay
2022-09-06 17:59 ` Jason Gunthorpe
2022-09-06 19:44 ` Oded Gabbay
2022-09-07 12:07 ` Christoph Hellwig
2022-09-07 12:05 ` Christoph Hellwig
2022-09-07 12:33 ` Jason Gunthorpe
2022-09-07 14:29 ` Christoph Hellwig
2022-09-07 14:46 ` Oded Gabbay
2022-09-07 15:23 ` Jason Gunthorpe
2022-09-07 15:32 ` Christoph Hellwig [this message]
2022-09-07 16:12 ` Jason Gunthorpe
2022-09-09 13:24 ` Christoph Hellwig
2022-09-09 14:09 ` Jason Gunthorpe
2022-09-07 16:31 ` Robin Murphy
2022-09-07 16:47 ` Jason Gunthorpe
2022-09-07 17:03 ` Dan Williams
2022-09-07 15:01 ` Robin Murphy
2022-09-07 12:03 ` Christoph Hellwig
2022-09-07 15:08 ` Christian König
2022-09-07 15:23 ` Christoph Hellwig
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