Re: [Qemu-devel] [RFC PATCH v2 3/3] VFIO: Type1 IOMMU mapping support for vGPU

[Neo Jia <cjia@nvidia.com>]

On Mon, Mar 07, 2016 at 02:07:15PM +0800, Jike Song wrote:
> Hi Neo,
> 
> On Fri, Mar 4, 2016 at 3:00 PM, Neo Jia <cjia@nvidia.com> wrote:
> > On Wed, Mar 02, 2016 at 04:38:34PM +0800, Jike Song wrote:
> >> On 02/24/2016 12:24 AM, Kirti Wankhede wrote:
> >> > +   vgpu_dma->size = map->size;
> >> > +
> >> > +   vgpu_link_dma(vgpu_iommu, vgpu_dma);
> >>
> >> Hi Kirti & Neo,
> >>
> >> seems that no one actually setup mappings for IOMMU here?
> >>
> >
> > Hi Jike,
> >
> > Yes.
> >
> > The actual mapping should be done by the host kernel driver after calling the
> > translation/pinning API vgpu_dma_do_translate.
> 
> Thanks for the reply. I mis-deleted the mail in my intel account, so
> reply with private mail account, sorry for that.
> 
> 
> In vgpu_dma_do_translate():
> 
> for (i = 0; i < count; i++) {
>    {snip}
>    dma_addr_t iova = gfn_buffer[i] << PAGE_SHIFT;
>    vgpu_dma = vgpu_find_dma(vgpu_iommu, iova, 0 /*  size */);
> 
>     remote_vaddr = vgpu_dma->vaddr + iova - vgpu_dma->iova;
>     if (get_user_pages_unlocked(NULL, mm, remote_vaddr, 1, 1, 0, page) == 1) {
>         pfn = page_to_pfn(page[0]);
>     }
>     gfn_buffer[i] = pfn;
> }
> 
> If I understand correctly, the purpose of above code, is given an
> array of gfns, try to pin & return associated pfns. There is still no
> IOMMU mappings here.  

Yes.

> Is it supposed to be the caller who should set
> up IOMMU by DMA api such as dma_map_page(), after calling
> vgpu_dma_do_translate()?
> 

Don't think you need to call dma_map_page here. Once you have the pfn available
to your GPU kernel driver, you can just go ahead to setup the mapping as you
normally do such as calling pci_map_sg and its friends.

Thanks,
Neo

> 
> -- 
> Thanks,
> Jike