On Thu, 23 Jan 2020 13:47:48 +0000 Alexandru Elisei <alexandru.elisei@xxxxxxx> wrote: Hi, > To get the size of the expansion ROM, software writes 0xfffff800 to the > expansion ROM BAR in the PCI configuration space. PCI emulation executes > the optional configuration space write callback that a device can > implement before emulating this write. > > VFIO doesn't have support for emulating expansion ROMs. With "VFIO doesn't have support" you mean kvmtool's VFIO implementation or the kernel's VFIO driver? Because to me it looks like it should work in the kernel, at least for the BAR sizing on the expansion ROM BAR: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/vfio/pci/vfio_pci_config.c#n477 Am I missing something here? QEMU seems to have code to load the ROM from the device and present that to the guest, but I am not sure exactly why. Cheers, Andre > However, the > callback writes the guest value to the hardware BAR, and then it reads > it back to the BAR to make sure the write has completed successfully. > > After this, we return to regular PCI emulation and because the BAR is > no longer 0, we write back to the BAR the value that the guest used to > get the size. As a result, the guest will think that the ROM size is > 0x800 after the subsequent read and we end up unintentionally exposing > to the guest a BAR which we don't emulate. > > Let's fix this by ignoring writes to the expansion ROM BAR. > > Signed-off-by: Alexandru Elisei <alexandru.elisei@xxxxxxx> > --- > vfio/pci.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/vfio/pci.c b/vfio/pci.c > index 1bdc20038411..1f38f90c3ae9 100644 > --- a/vfio/pci.c > +++ b/vfio/pci.c > @@ -472,6 +472,9 @@ static void vfio_pci_cfg_write(struct kvm *kvm, struct pci_device_header *pci_hd > struct vfio_device *vdev; > void *base = pci_hdr; > > + if (offset == PCI_ROM_ADDRESS) > + return; > + > pdev = container_of(pci_hdr, struct vfio_pci_device, hdr); > vdev = container_of(pdev, struct vfio_device, pci); > info = &vdev->regions[VFIO_PCI_CONFIG_REGION_INDEX].info;
