On 2016年12月22日 19:04, Peter Xu wrote:
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).
Just for switching? This seems an overkill since we don't depends on it
for all other things. Guest should setup correct mappings by explicitly
notify device IOTLB. A quick glance at ATS spec, for enabling and
disabling, looks like it was done through enable bit of ASTctl instead
of here.
So we are probably ok here :)
However, I think the bigger issue is we still don't have a dynamic way
to turn vhost DMAR on/off, right?
The API was ready for this, just issue another set_feature ioctl without
IOMMU_PLATFORM. (But unfortunately, vhost need a small patch to make
this work).
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).
For vhost part, the changes should be very minor, probably just:
- a patch to make sure vhost can disable device IOTLB during feature set
- properly handling enabling bit of ATSctl in qemu (probably through an
notifier)
(However I do think this is an improvement to current VT-d though)
Thanks,
-- peterx
+1. We should try to emulate exactly what hardware does to avoid
breaking all kinds of guest or userspace drivers.
Thanks
