On 09-07-2021 17:13, 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.
>
> Signed-off-by: Wei Liu <wei....@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]);
Is there a possibility of pci_devs_to_skip + pos > sizeof(pci_devs_to_skip) and
also a valid memory ?
I would recommend to have a check of size as well before accessing the array
content, just to be safer accessing any memory.
> + }
> +
> vdev = kzalloc(sizeof(*vdev), GFP_KERNEL);
> if (!vdev)
> return ERR_PTR(-ENOMEM);
>
Regards,
~Praveen.
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