linux-kernel - Re: [RFC PATCH v2] uacce: Add uacce

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Message-ID: <20210201234424.GI4718@ziepe.ca>
Date:   Mon, 1 Feb 2021 19:44:24 -0400
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     "Tian, Kevin" <kevin.tian@...el.com>
Cc:     "Song Bao Hua (Barry Song)" <song.bao.hua@...ilicon.com>,
        "chensihang (A)" <chensihang1@...ilicon.com>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Zhangfei Gao <zhangfei.gao@...aro.org>,
        "Liguozhu (Kenneth)" <liguozhu@...ilicon.com>,
        "linux-accelerators@...ts.ozlabs.org" 
        <linux-accelerators@...ts.ozlabs.org>
Subject: Re: [RFC PATCH v2] uacce: Add uacce_ctrl misc device

On Fri, Jan 29, 2021 at 10:09:03AM +0000, Tian, Kevin wrote:
> > SVA is not doom to work with IO page fault only. If we have SVA+pin,
> > we would get both sharing address and stable I/O latency.
> 
> Isn't it like a traditional MAP_DMA API (imply pinning) plus specifying 
> cpu_va of the memory pool as the iova? 

I think their issue is the HW can't do the cpu_va trick without also
involving the system IOMMU in a SVA mode

It really is something that belongs under some general /dev/sva as we
talked on the vfio thread

Jason