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

[Liu, Yi L]

> -----Original Message-----
> From: Jason Wang [mailto:address@hidden
> Sent: Thursday, February 16, 2017 1:44 PM
> To: Liu, Yi L <address@hidden>; Michael S. Tsirkin <address@hidden>; qemu-
> address@hidden
> Cc: Peter Maydell <address@hidden>; Eduardo Habkost
> <address@hidden>; Peter Xu <address@hidden>; Paolo Bonzini
> <address@hidden>; Richard Henderson <address@hidden>; Tian, Kevin
> <address@hidden>; Lan, Tianyu <address@hidden>; Alex Williamson
> <address@hidden>
> Subject: Re: [Qemu-devel] [PULL 08/41] intel_iommu: support device iotlb
> descriptor
> 
> 
> 
> 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.

Jason, for assigned device, I think guest could see ATS if the assigned device
supports ATS. I can see it when passthru iGPU.

Regards,
Yi L