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From: Jason Gunthorpe <jgg@ziepe.ca>
To: "Xiong, Jianxin" <jianxin.xiong@intel.com>
Cc: "linux-rdma@vger.kernel.org" <linux-rdma@vger.kernel.org>,
	Doug Ledford <dledford@redhat.com>,
	Sumit Semwal <sumit.semwal@linaro.org>,
	Leon Romanovsky <leon@kernel.org>,
	"Vetter, Daniel" <daniel.vetter@intel.com>,
	Christian Koenig <christian.koenig@amd.com>,
	"dri-devel@lists.freedesktop.org"
	<dri-devel@lists.freedesktop.org>
Subject: Re: [RFC PATCH v2 0/3] RDMA: add dma-buf support
Date: Thu, 2 Jul 2020 09:27:36 -0300
Message-ID: <20200702122736.GR25301@ziepe.ca> (raw)
In-Reply-To: <MW3PR11MB4555223B6D3C6E4829795798E56F0@MW3PR11MB4555.namprd11.prod.outlook.com>

On Tue, Jun 30, 2020 at 08:08:46PM +0000, Xiong, Jianxin wrote:
> > From: Jason Gunthorpe <jgg@ziepe.ca>
> > Sent: Tuesday, June 30, 2020 12:17 PM
> > To: Xiong, Jianxin <jianxin.xiong@intel.com>
> > Cc: linux-rdma@vger.kernel.org; Doug Ledford <dledford@redhat.com>; Sumit Semwal <sumit.semwal@linaro.org>; Leon Romanovsky
> > <leon@kernel.org>; Vetter, Daniel <daniel.vetter@intel.com>; Christian Koenig <christian.koenig@amd.com>; dri-
> > devel@lists.freedesktop.org
> > Subject: Re: [RFC PATCH v2 0/3] RDMA: add dma-buf support
> > 
> > > >
> > > > On Tue, Jun 30, 2020 at 05:21:33PM +0000, Xiong, Jianxin wrote:
> > > > > > > Heterogeneous Memory Management (HMM) utilizes
> > > > > > > mmu_interval_notifier and ZONE_DEVICE to support shared
> > > > > > > virtual address space and page migration between system memory
> > > > > > > and device memory. HMM doesn't support pinning device memory
> > > > > > > because pages located on device must be able to migrate to
> > > > > > > system memory when accessed by CPU. Peer-to-peer access is
> > > > > > > possible if the peer can handle page fault. For RDMA, that means the NIC must support on-demand paging.
> > > > > >
> > > > > > peer-peer access is currently not possible with hmm_range_fault().
> > > > >
> > > > > Currently hmm_range_fault() always sets the cpu access flag and
> > > > > device private pages are migrated to the system RAM in the fault handler.
> > > > > However, it's possible to have a modified code flow to keep the
> > > > > device private page info for use with peer to peer access.
> > > >
> > > > Sort of, but only within the same device, RDMA or anything else generic can't reach inside a DEVICE_PRIVATE and extract anything
> > useful.
> > >
> > > But pfn is supposed to be all that is needed.
> > 
> > Needed for what? The PFN of the DEVICE_PRIVATE pages is useless for anything.
> 
> Hmm. I thought the pfn corresponds to the address in the BAR range. I could be
> wrong here. 

No, DEVICE_PRIVATE is a dummy pfn to empty address space.

Jason

  reply index

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-29 17:31 Jianxin Xiong
2020-06-29 17:31 ` [RFC PATCH v2 1/3] RDMA/umem: Support importing dma-buf as user memory region Jianxin Xiong
2020-06-30 19:04   ` Xiong, Jianxin
2020-06-29 17:31 ` [RFC PATCH v2 2/3] RDMA/core: Expand the driver method 'reg_user_mr' to support dma-buf Jianxin Xiong
2020-06-30 19:04   ` Xiong, Jianxin
2020-06-29 17:31 ` [RFC PATCH v2 3/3] RDMA/uverbs: Add uverbs command for dma-buf based MR registration Jianxin Xiong
2020-06-30 19:05   ` Xiong, Jianxin
2020-06-29 18:51 ` [RFC PATCH v2 0/3] RDMA: add dma-buf support Jason Gunthorpe
2020-06-30 17:21   ` Xiong, Jianxin
2020-06-30 17:34     ` Jason Gunthorpe
2020-06-30 18:46       ` Xiong, Jianxin
2020-06-30 19:17         ` Jason Gunthorpe
2020-06-30 20:08           ` Xiong, Jianxin
2020-07-02 12:27             ` Jason Gunthorpe [this message]
2020-07-01  9:03         ` Christian König
2020-07-01 12:07           ` Daniel Vetter
2020-07-01 12:14             ` Daniel Vetter
2020-07-01 12:39           ` Jason Gunthorpe
2020-07-01 12:55             ` Christian König
2020-07-01 15:42               ` Daniel Vetter
2020-07-01 17:15                 ` Jason Gunthorpe
2020-07-02 13:10                   ` Daniel Vetter
2020-07-02 13:29                     ` Jason Gunthorpe
2020-07-02 14:50                       ` Christian König
2020-07-02 18:15                         ` Daniel Vetter
2020-07-03 12:03                           ` Jason Gunthorpe
2020-07-03 12:52                             ` Daniel Vetter
2020-07-03 13:14                               ` Jason Gunthorpe
2020-07-03 13:21                                 ` Christian König
2020-07-07 21:58                                   ` Xiong, Jianxin
2020-07-08  9:38                                     ` Christian König
2020-07-08  9:49                                       ` Daniel Vetter
2020-07-08 14:20                                         ` Christian König
2020-07-08 14:33                                           ` Alex Deucher
2020-06-30 18:56 ` Xiong, Jianxin

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