On Wed, 24 May 2023, Jan Beulich wrote: > >> RFC: _setup_hwdom_pci_devices()' loop may want splitting: For > >> modify_bars() to consistently respect BARs of hidden devices while > >> setting up "normal" ones (i.e. to avoid as much as possible the > >> "continue" path introduced here), setting up of the former may want > >> doing first. > > > > But BARs of hidden devices should be mapped into dom0 physmap? > > Yes.
The BARs would be mapped read-only (not read-write), right? Otherwise we let dom0 access devices that belong to Xen, which doesn't seem like a good idea. But even if we map the BARs read-only, what is the benefit of mapping them to Dom0? If Dom0 loads a driver for it and the driver wants to initialize the device, the driver will crash because the MMIO region is read-only instead of read-write, right? How does this device hiding work for dom0? How does dom0 know not to access a device that is present on the PCI bus but is used by Xen? The reason why I was suggesting to hide the device completely in the past was that I assumed we had to hide the device (make it "disappear" on the PCI bus) otherwise Dom0 would access it. Is there another way to mark a PCI devices as "inaccessible" or "disabled"?
