Re: [Qemu-devel] [PATCH RFC v4 18/20] intel_iommu: enable vfio devices

[Jason Wang]

On 2017年01月22日 17:04, Peter Xu wrote:
> On Sun, Jan 22, 2017 at 04:08:04PM +0800, Jason Wang wrote:
>
> [...]
>
> > > +static void vtd_iotlb_page_invalidate_notify(IntelIOMMUState *s,
> > > +                                           uint16_t domain_id, hwaddr addr,
> > > +                                           uint8_t am)
> > > +{
> > > +    IntelIOMMUNotifierNode *node;
> > > +    VTDContextEntry ce;
> > > +    int ret;
> > > +
> > > +    QLIST_FOREACH(node, &(s->notifiers_list), next) {
> > > +        VTDAddressSpace *vtd_as = node->vtd_as;
> > > +        ret = vtd_dev_to_context_entry(s, pci_bus_num(vtd_as->bus),
> > > +                                       vtd_as->devfn, &ce);
> > > +        if (!ret && domain_id == VTD_CONTEXT_ENTRY_DID(ce.hi)) {
> > > +            vtd_page_walk(&ce, addr, addr + (1 << am) * VTD_PAGE_SIZE,
> > > +                          vtd_page_invalidate_notify_hook,
> > > +                          (void *)&vtd_as->iommu, true);
> > Why not simply trigger the notifier here? (or is this vfio required?)
> Because we may only want to notify part of the region - we are with
> mask here, but not exact size.
>
> Consider this: guest (with caching mode) maps 12K memory (4K*3 pages),
> the mask will be extended to 16K in the guest. In that case, we need
> to explicitly go over the page entry to know that the 4th page should
> not be notified.

I see. Then it was required by vfio only, I think we can add a fast path 
for !CM in this case by triggering the notifier directly.

Another possible issue is, consider (with CM) a 16K contiguous iova with 
the last page has already been mapped. In this case, if we want to map 
first three pages, when handling IOTLB invalidation, am would be 16K, 
then the last page will be mapped twice. Can this lead some issue?

Thanks