On Thu, Dec 21, 2023 at 01:19:18PM +0000, Catalin Marinas wrote: > If we really want to avoid any aliases (though I think we are spending > too many cycles on something that's not a real issue), the only way is > to have fd-based mappings in KVM so that there's no VMM alias. After > that we need to choose between (2) and (3) since the VMM may no longer > be able to probe the device and figure out which ranges need what > attributes. If we use a FD then KVM will be invoking some API on the FD to get the physical memory addreses and we can have that API also return information on the allowed memory types. > > Kinda stinks to make the VMM aware of the device, but IMO it is a > > fundamental limitation of the way we back memslots right now. > > As I mentioned above, the limitation may be more complex if the > intra-BAR attributes are not something readily available in the device > documentation. Maybe Jason or Ankit can shed some light here: are those > intra-BAR ranges configurable by the (guest) driver or they are already > pre-configured by firmware and the driver only needs to probe them? Configured by the guest on the fly, on a page by page basis. There is no way for the VMM to pre-predict what memory type the VM will need. The VM must be in control of this. Jason
