Re: [Qemu-devel] [PATCH v4 RESEND 0/3] IOMMU: intel_iommu support map and unmap notifications

[Alex Williamson <alex.williamson@redhat.com>]

[cc +david]

On Thu, 20 Oct 2016 22:17:18 +0300
"Aviv B.D." <bd.aviv@gmail.com> wrote:

> On Mon, Oct 17, 2016 at 7:07 PM, Alex Williamson <alex.williamson@redhat.com
> > wrote:  
> 
> > On Mon, 17 Oct 2016 18:44:21 +0300
> > "Aviv B.D" <bd.aviv@gmail.com> wrote:
> >  
> > > From: "Aviv Ben-David" <bd.aviv@gmail.com>
> > >
> > > * Advertize Cache Mode capability in iommu cap register.
> > >   This capability is controlled by "cache-mode" property of intel-iommu  
> > device.  
> > >   To enable this option call QEMU with "-device  
> > intel-iommu,cache-mode=true".  
> > >
> > > * On page cache invalidation in intel vIOMMU, check if the domain belong  
> > to  
> > >   registered notifier, and notify accordingly.
> > >
> > > Currently this patch still doesn't enabling VFIO devices support with  
> > vIOMMU  
> > > present. Current problems:
> > > * vfio_iommu_map_notify is not aware about memory range belong to  
> > specific  
> > >   VFIOGuestIOMMU.  
> >
> > Could you elaborate on why this is an issue?
> >  
> 
> In my setup the VFIO registered two memory areas with one page of
> unregistered memory
> between them.
> 
> When I'm calling memory_region_notify_iommu it calls the notifier function
> of VFIO twice
> when the second time is failing with warning to console as the new mapping
> is already present.
> 
> The notifier function of VFIO should ignore IOMMUTLBEntry that is not in
> the correct
> range.

Hmm, right vfio_listener_region_add() is called for a
MemoryRegionSection, but then we add an iommu notifier to the
MemoryRegion, so we end up with a notifier per MemoryRegionSection
regardless of whether they're backed by the same MemoryRegion.  Seems
like we need a MemoryRegion based list of VFIOGuestIOMMUs so we only
register once per MemoryRegion and then sort though the list of
VFIOGuestIOMMUs for a given MemoryRegion to find the one affected.
David, does that sound right to you?

I am curious why you get two regions separated by one page, can you
give an example of the ranges for each?  Thanks,

Alex