Re: [RFC PATCH 2/6] dma-buf: Add get_phys() to describe a physical run

[Fred Griffoul]

On 10/5/26 Christian König wrote:
> Well filling page tables by the importer is an absolutely clear NO-GO
> for the DMA-buf design, we have gotten down that path already and it
> took us years to remove this functionality again.

Understood, thanks for the quick and clear answers on this patch and on
patch 3.

> The problem you are facing here is that dma_buf_mmap() doesn't work
> because you don't have a VMA.

Right: the memory has no struct page and is deliberately not mapped in
the host, so there is no VMA to hand to KVM.

I'll post a new version of this series. It drops get_phys(), the ranged
invalidation and the guest_memfd dma-buf import (patches 2-5), and it
does not touch drivers/dma-buf, as you suggested in the PAL discussion:

  https://lore.kernel.org/all/c413710b-4c28-4ed8-88ec-aeb8c4482011@xxxxxxx/

KVM gets its frames through the KVM-private guest_memfd provider
interface from David's series. iommufd gets them through a private
interface with the exporter, as it already does for vfio-pci. The new
version adds a small registry in iommufd for that, which replaces the
symbol_get() of the sample in David's series. The dma-buf is then only
the handle and the existing revoke.

Thanks,
Fred