RE: [RFC v3 2/3] virtio: Introduce Vdmabuf driver

["Kasireddy, Vivek" <vivek.kasireddy@intel.com>]

Hi Christian,

> 
> Hi Vivek,
> 
> > [Kasireddy, Vivek] What if I do mmap() on the fd followed by mlock()
> > or mmap() followed by get_user_pages()? If it still fails, would
> > ioremapping the device memory and poking at the backing storage be an
> > option? Or, if I bind the passthrough'd GPU device to vfio-pci and tap
> > into the memory region associated with the device memory, can it be made to work?
> 
> get_user_pages() is not allowed on mmaped DMA-bufs in the first place.
> 
> Daniel is currently adding code to make sure that this is never ever used.
> 
> > And, I noticed that for PFNs that do not have valid struct page
> > associated with it, KVM does a memremap() to access/map them. Is this an option?
> 
> No, even for system memory which has a valid struct page touching it when it is part of a
> DMA-buf is illegal since the reference count and mapping fields in struct page might be
> used for something different.
> 
> Keep in mind that struct page is a heavily overloaded structure for different use cases. You
> can't just use it for a different use case than what the owner of the page has intended it.
[Kasireddy, Vivek] What is your recommended/acceptable way for doing what I am trying to 
do?

Thanks,
Vivek

> 
> Regards,
> Christian.
> 
> >
> >
> > Thanks,
> > Vivek
> >> take care,
> >>    Gerd