Re: [Qemu-devel] [IGDVFIO] [PATCH 3/8] RFC and help completing: Intel IGD Direct Assignment with VFIO

[Paolo Bonzini <pbonzini@redhat.com>]

Il 24/09/2014 22:57, Alex Williamson ha scritto:
> Right, that's the physical mapping, Andy's patches are mimicking that
> behavior virtually.  Seabios reserves memory, creates e820 entries, and
> "maps" the hardware by writing to these registers.  That triggers QEMU
> to adjust the MemoryRegion in the guest address space which is an mmap
> to the host address space, using /dev/mem for now, but hopefully the
> vfio file descriptor in the future (I should be careful what I hope
> for).

Yeah, I remember discussing that with Andrew on IRC.  So he did
implement that idea.

> The opregion is pretty trivial because the write is to the IGD itself.
> The others are to the host bridge, so we need to figure out what sort of
> abstraction makes sense to get that back into vfio code.

Do we have to support all chipsets?  IIUC the more recent devices need
fewer and fewer "backdoors".

Paolo

> Perhaps vfio creates all the memory regions and registers them into an
> igd service and the host bridge can make calls like:
> 
> gtt = igd_get_gtt_mr();
> 
> which returns NULL and nothing happens or the registered MemoryRegion
> and the host bridge places it into the address space.  Thanks,