Robin Murphy
2021-Jul-09 12:46 UTC
[RFC v1 6/8] mshv: command line option to skip devices in PV-IOMMU
On 2021-07-09 12:43, Wei Liu wrote:> Some devices may have been claimed by the hypervisor already. One such > example is a user can assign a NIC for debugging purpose. > > Ideally Linux should be able to tell retrieve that information, but > there is no way to do that yet. And designing that new mechanism is > going to take time. > > Provide a command line option for skipping devices. This is a stopgap > solution, so it is intentionally undocumented. Hopefully we can retire > it in the future.Huh? If the host is using a device, why the heck is it exposing any knowledge of that device to the guest at all, let alone allowing the guest to do anything that could affect its operation!? Robin.> Signed-off-by: Wei Liu <wei.liu at kernel.org> > --- > drivers/iommu/hyperv-iommu.c | 45 ++++++++++++++++++++++++++++++++++++ > 1 file changed, 45 insertions(+) > > diff --git a/drivers/iommu/hyperv-iommu.c b/drivers/iommu/hyperv-iommu.c > index 043dcff06511..353da5036387 100644 > --- a/drivers/iommu/hyperv-iommu.c > +++ b/drivers/iommu/hyperv-iommu.c > @@ -349,6 +349,16 @@ static const struct irq_domain_ops hyperv_root_ir_domain_ops = { > > #ifdef CONFIG_HYPERV_ROOT_PVIOMMU > > +/* The IOMMU will not claim these PCI devices. */ > +static char *pci_devs_to_skip; > +static int __init mshv_iommu_setup_skip(char *str) { > + pci_devs_to_skip = str; > + > + return 0; > +} > +/* mshv_iommu_skip=(SSSS:BB:DD.F)(SSSS:BB:DD.F) */ > +__setup("mshv_iommu_skip=", mshv_iommu_setup_skip); > + > /* DMA remapping support */ > struct hv_iommu_domain { > struct iommu_domain domain; > @@ -774,6 +784,41 @@ static struct iommu_device *hv_iommu_probe_device(struct device *dev) > if (!dev_is_pci(dev)) > return ERR_PTR(-ENODEV); > > + /* > + * Skip the PCI device specified in `pci_devs_to_skip`. This is a > + * temporary solution until we figure out a way to extract information > + * from the hypervisor what devices it is already using. > + */ > + if (pci_devs_to_skip && *pci_devs_to_skip) { > + int pos = 0; > + int parsed; > + int segment, bus, slot, func; > + struct pci_dev *pdev = to_pci_dev(dev); > + > + do { > + parsed = 0; > + > + sscanf(pci_devs_to_skip + pos, > + " (%x:%x:%x.%x) %n", > + &segment, &bus, &slot, &func, &parsed); > + > + if (parsed <= 0) > + break; > + > + if (pci_domain_nr(pdev->bus) == segment && > + pdev->bus->number == bus && > + PCI_SLOT(pdev->devfn) == slot && > + PCI_FUNC(pdev->devfn) == func) > + { > + dev_info(dev, "skipped by MSHV IOMMU\n"); > + return ERR_PTR(-ENODEV); > + } > + > + pos += parsed; > + > + } while (pci_devs_to_skip[pos]); > + } > + > vdev = kzalloc(sizeof(*vdev), GFP_KERNEL); > if (!vdev) > return ERR_PTR(-ENOMEM); >