On Fri, 29 Jul 2022 21:43:44 +0300 Cosmin Chenaru <cosmin.chen...@gmail.com> wrote:
> Hi, > > I have an Intel network card inside a VM using PCI-Passthrough and I would > like to write one register (the Physical Hardware Clock) but from inside > the host, as writing it from inside the VM is complicated with all the > unstable vTSC or other time sensitive tools which don't work best from > inside a VM. > > I know that I cannot write it from the host's network driver, as the driver > will unbind the card when starting the VM, so let's say I write the > register from another place (either hacking the network driver or from the > VFIO driver). Do you think this would be possible? > > Also, should I worry about locking the access so that the host and VM don't > write to the PCI config space at the same time? I watched Alex's VFIO > presentations and I understand that through Memory Mapped IO the VM can > directly write the PCI config space, so the host will not be able to > intercept and, in my case, to do the locking. > > And my apologies if these questions were asked before. I did do a quick > search but could not find anything relevant. If you want special handling of the device in the host then you could write a vfio-pci variant driver, see for instance the mlx5 one recently added, and do the register write at an opportune time. I'm a bit dubious why this can't be written in the guest though. If you want the simplest means to poke the register from the host, see setpci(8). I don't think you need any special locking, all config space accesses come in through read/write operations to the config space region and go through the same accessor functions that setpci would use. Thanks, Alex _______________________________________________ vfio-users mailing list vfio-users@redhat.com https://listman.redhat.com/mailman/listinfo/vfio-users
