Re: [Qemu-devel] [PULL 08/41] intel_iommu: support device iotlb descriptor

[Jason Wang]

On 2017年02月16日 13:43, Jason Wang wrote:
> On 2017年02月16日 13:36, Liu, Yi L wrote:
> > > -----Original Message-----
> > > From: Qemu-devel 
> > > [mailto:address@hidden
> > > On Behalf Of Michael S. Tsirkin
> > > Sent: Tuesday, January 10, 2017 1:40 PM
> > > To: address@hidden
> > > Cc: Peter Maydell <address@hidden>; Eduardo Habkost
> > > <address@hidden>; Jason Wang <address@hidden>; Peter Xu
> > > <address@hidden>; Paolo Bonzini <address@hidden>; Richard
> > > Henderson <address@hidden>
> > > Subject: [Qemu-devel] [PULL 08/41] intel_iommu: support device iotlb
> > > descriptor
> > >
> > > From: Jason Wang <address@hidden>
> > >
> > > This patch enables device IOTLB support for intel iommu. The major 
> > > work is to
> > > implement QI device IOTLB descriptor processing and notify the 
> > > device through
> > > iommu notifier.
> > Hi Jason/Michael,
> >
> > Recently Peter Xu's patch also touched intel-iommu emulation. His 
> > patch shadows
> > second-level page table by capturing iotlb flush from guest. It would 
> > result in page
> > table updating in host. Does this patch also use the same map/umap 
> > API provided
> > by VFIO?
>
> Yes, it depends on the iommu notifier too.
>
> > If it is, then I think it would also update page table in host. It 
> > looks to be
> > a duplicate update. Pls refer to the following snapshot captured from 
> > section 6.5.2.5
> > of vtd spec.
> >
> > "Since translation requests from a device may be serviced by hardware 
> > from the IOTLB, software must
> > always request IOTLB invalidation (iotlb_inv_dsc) before requesting 
> > corresponding Device-TLB
> > (dev_tlb_inv_dsc) invalidation."
> >
> > Maybe for device-iotlb, we need a separate API which just pass down 
> > the invalidate
> > info without updating page table. Any thoughts?
>
> cc Alex.
>
> If we want ATS to be visible for guest (but I'm not sure if VFIO 
> support this), we probably need another notifier or a new flag.
>
> Thanks 

Or need a dedicated address_space if ATS were enabled for the device.