On 2017/10/12 17:50, Liu, Yi L wrote: > > >> -----Original Message----- >> From: Bob Liu [mailto:liub...@huawei.com] >> Sent: Thursday, October 12, 2017 5:39 PM >> To: Jean-Philippe Brucker <jean-philippe.bruc...@arm.com>; Joerg Roedel >> <j...@8bytes.org>; Liu, Yi L <yi.l....@intel.com> >> Cc: Lan, Tianyu <tianyu....@intel.com>; Liu, Yi L >> <yi.l....@linux.intel.com>; Greg >> Kroah-Hartman <gre...@linuxfoundation.org>; Wysocki, Rafael J >> <rafael.j.wyso...@intel.com>; LKML <linux-kernel@vger.kernel.org>; >> io...@lists.linux-foundation.org; David Woodhouse <dw...@infradead.org> >> Subject: Re: [PATCH v2 03/16] iommu: introduce iommu invalidate API function >> >> On 2017/10/11 20:48, Jean-Philippe Brucker wrote: >>> On 11/10/17 13:15, Joerg Roedel wrote: >>>> On Wed, Oct 11, 2017 at 11:54:52AM +0000, Liu, Yi L wrote: >>>>> I didn't quite get 'iovm' mean. Can you explain a bit about the idea? >>>> >>>> It's short for IO Virtual Memory, basically a replacement term for 'svm' >>>> that is not ambiguous (afaik) and not specific to Intel. >>> >>> I wonder if SVM originated in OpenCL first, rather than intel? That's >>> why I'm using it, but it is ambiguous. I'm not sure IOVM is precise >>> enough though, since the name could as well be used without shared >>> tables, for classical map/unmap and IOVAs. Kevin Tian suggested SVA >>> "Shared Virtual Addressing" last time, which is a little more clear >>> than SVM and isn't used elsewhere in the kernel either. >>> >> >> The process "vaddr" can be the same as "IOVA" by using the classical >> map/unmap >> way. >> This is also a kind of share virtual memory/address(except have to pin >> physical >> memory). >> How to distinguish these two different implementation of "share virtual >> memory/address"? >> > [Liu, Yi L] Not sure if I get your idea well. Process "vaddr" is owned by > process and > maintained by mmu, while "IOVA" is maintained by iommu. So they are different > in the > way they are maintained. Since process "vaddr" is maintained by mmu and then > used by > iommu, so we call it shared virtual memory/address. This is how "shared" term > comes.
I think from the view of application, the share virtual memory/address(or Nvidia-CUDA unify virtual address) is like this: 1. vaddr = malloc(); e.g vaddr=0x10000 2. device can get the same data(accessing the same physical memory) through same address e.g 0x10000, and don't care about it's a vaddr or IOVA.. (actually in Nvidia-cuda case, the data will be migrated between system-ddr and gpu-memory, but the vaddr is always the same for CPU and GPU). So there are two ways(beside Nvidia way) to implement this requirement: 1) get the physical memory of vaddr; dma_map the paddr to iova; If we appoint iova = vaddr (e.g iova can be controlled by the user space driver through vfio DMA_MAP), This can also be called share virtual address between CPU process and device.. 2) The second way is what this RFC did.
