Re: [Qemu-devel] [PATCH v3] intel_iommu: allow dynamic switch of IOMMU region

[Peter Xu]

On Thu, Dec 22, 2016 at 05:52:58PM +0800, Jason Wang wrote:
> 
> 
> On 2016年12月22日 17:48, Peter Xu wrote:
> >  /* Handle Translation Enable/Disable */
> >  static void vtd_handle_gcmd_te(IntelIOMMUState *s, bool en)
> >  {
> >+    if (s->dmar_enabled == en) {
> >+        return;
> >+    }
> >+
> >      VTD_DPRINTF(CSR, "Translation Enable %s", (en ? "on" : "off"));
> >      if (en) {
> >@@ -1196,6 +1237,8 @@ static void vtd_handle_gcmd_te(IntelIOMMUState *s, 
> >bool en)
> >          /* Ok - report back to driver */
> >          vtd_set_clear_mask_long(s, DMAR_GSTS_REG, VTD_GSTS_TES, 0);
> >      }
> >+
> >+    vtd_switch_address_space_all(s, en);
> >  }
> 
> We may need something like notifier here to tell e.g vhost to stop device
> IOTLB. (Since it's likely this series were applied after device IOTLB
> patches)

Yes, I missed vhost case.

To notify vhost, IMO we should be able to use memory listeners just
like how vfio devices do (please refer to vfio_memory_listener).
However, I think the bigger issue is we still don't have a dynamic way
to turn vhost DMAR on/off, right?

If so, we may need to re-touch all the parts to enable the dynamic
switching of DMA remapping - QEMU vhost, kernel vhost, and virtio on
the guest side... I start to doubt whether that effort will worth it
due to this single change, especially if this feature (dynamic on/off
DMA remapping) won't be used by most VMs (i.e., Linux should only turn
VT-d on when kernel detects it, and should never turn it off in
anyway).

(However I do think this is an improvement to current VT-d though)

Thanks,

-- peterx