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SubjectRe: [PATCH v2 03/16] iommu: introduce iommu invalidate API function
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On 2017/10/12 17:50, Liu, Yi L wrote:
>
>
>> -----Original Message-----
>> From: Bob Liu [mailto:liubo95@huawei.com]
>> Sent: Thursday, October 12, 2017 5:39 PM
>> To: Jean-Philippe Brucker <jean-philippe.brucker@arm.com>; Joerg Roedel
>> <joro@8bytes.org>; Liu, Yi L <yi.l.liu@intel.com>
>> Cc: Lan, Tianyu <tianyu.lan@intel.com>; Liu, Yi L <yi.l.liu@linux.intel.com>; Greg
>> Kroah-Hartman <gregkh@linuxfoundation.org>; Wysocki, Rafael J
>> <rafael.j.wysocki@intel.com>; LKML <linux-kernel@vger.kernel.org>;
>> iommu@lists.linux-foundation.org; David Woodhouse <dwmw2@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.


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