Re: kvm PCI assignment & VFIO ramblings

Roedel, Joerg
2011-08-25T10:54:02Z

Hi Alex,

On Wed, Aug 24, 2011 at 05:13:49PM -0400, Alex Williamson wrote:
> Is this roughly what you're thinking of for the iommu_group component?
> Adding a dev_to_group iommu ops callback let's us consolidate the sysfs
> support in the iommu base. Would AMD-Vi do something similar (or
> exactly the same) for group #s? Thanks,

The concept looks good, I have some comments, though. On AMD-Vi the
implementation would look a bit different because there is a
data-structure were the information can be gathered from, so no need for
PCI bus scanning there.

> diff --git a/drivers/base/iommu.c b/drivers/base/iommu.c
> index 6e6b6a1..6b54c1a 100644
> --- a/drivers/base/iommu.c
> +++ b/drivers/base/iommu.c
> @@ -17,20 +17,56 @@
> */
>
> #include <linux/bug.h>
> +#include <linux/device.h>
> #include <linux/types.h>
> #include <linux/module.h>
> #include <linux/slab.h>
> #include <linux/errno.h>
> #include <linux/iommu.h>
> +#include <linux/pci.h>
>
> static struct iommu_ops *iommu_ops;
>
> +static ssize_t show_iommu_group(struct device *dev,
> + struct device_attribute *attr, char *buf)
> +{
> + return sprintf(buf, "%lx", iommu_dev_to_group(dev));

Probably add a 0x prefix so userspace knows the format?

> +}
> +static DEVICE_ATTR(iommu_group, S_IRUGO, show_iommu_group, NULL);
> +
> +static int add_iommu_group(struct device *dev, void *unused)
> +{
> + if (iommu_dev_to_group(dev) >= 0)
> + return device_create_file(dev, &dev_attr_iommu_group);
> +
> + return 0;
> +}
> +
> +static int device_notifier(struct notifier_block *nb,
> + unsigned long action, void *data)
> +{
> + struct device *dev = data;
> +
> + if (action == BUS_NOTIFY_ADD_DEVICE)
> + return add_iommu_group(dev, NULL);
> +
> + return 0;
> +}
> +
> +static struct notifier_block device_nb = {
> + .notifier_call = device_notifier,
> +};
> +
> void register_iommu(struct iommu_ops *ops)
> {
> if (iommu_ops)
> BUG();
>
> iommu_ops = ops;
> +
> + /* FIXME - non-PCI, really want for_each_bus() */
> + bus_register_notifier(&pci_bus_type, &device_nb);
> + bus_for_each_dev(&pci_bus_type, NULL, NULL, add_iommu_group);
> }

We need to solve this differently. ARM is starting to use the iommu-api
too and this definitly does not work there. One possible solution might
be to make the iommu-ops per-bus.

> bool iommu_found(void)
> @@ -94,6 +130,14 @@ int iommu_domain_has_cap(struct iommu_domain *domain,
> }
> EXPORT_SYMBOL_GPL(iommu_domain_has_cap);
>
> +long iommu_dev_to_group(struct device *dev)
> +{
> + if (iommu_ops->dev_to_group)
> + return iommu_ops->dev_to_group(dev);
> + return -ENODEV;
> +}
> +EXPORT_SYMBOL_GPL(iommu_dev_to_group);

Please rename this to iommu_device_group(). The dev_to_group name
suggests a conversion but it is actually just a property of the device.
Also the return type should not be long but something that fits into
32bit on all platforms. Since you use -ENODEV, probably s32 is a good
choice.

> +
> int iommu_map(struct iommu_domain *domain, unsigned long iova,
> phys_addr_t paddr, int gfp_order, int prot)
> {
> diff --git a/drivers/pci/intel-iommu.c b/drivers/pci/intel-iommu.c
> index f02c34d..477259c 100644
> --- a/drivers/pci/intel-iommu.c
> +++ b/drivers/pci/intel-iommu.c
> @@ -404,6 +404,7 @@ static int dmar_map_gfx = 1;
> static int dmar_forcedac;
> static int intel_iommu_strict;
> static int intel_iommu_superpage = 1;
> +static int intel_iommu_no_mf_groups;
>
> #define DUMMY_DEVICE_DOMAIN_INFO ((struct device_domain_info *)(-1))
> static DEFINE_SPINLOCK(device_domain_lock);
> @@ -438,6 +439,10 @@ static int __init intel_iommu_setup(char *str)
> printk(KERN_INFO
> "Intel-IOMMU: disable supported super page\n");
> intel_iommu_superpage = 0;
> + } else if (!strncmp(str, "no_mf_groups", 12)) {
> + printk(KERN_INFO
> + "Intel-IOMMU: disable separate groups for multifunction devices\n");
> + intel_iommu_no_mf_groups = 1;

This should really be a global iommu option and not be VT-d specific.

>
> str += strcspn(str, ",");
> @@ -3902,6 +3907,52 @@ static int intel_iommu_domain_has_cap(struct iommu_domain *domain,
> return 0;
> }
>
> +/* Group numbers are arbitrary. Device with the same group number
> + * indicate the iommu cannot differentiate between them. To avoid
> + * tracking used groups we just use the seg|bus|devfn of the lowest
> + * level we're able to differentiate devices */
> +static long intel_iommu_dev_to_group(struct device *dev)
> +{
> + struct pci_dev *pdev = to_pci_dev(dev);
> + struct pci_dev *bridge;
> + union {
> + struct {
> + u8 devfn;
> + u8 bus;
> + u16 segment;
> + } pci;
> + u32 group;
> + } id;
> +
> + if (iommu_no_mapping(dev))
> + return -ENODEV;
> +
> + id.pci.segment = pci_domain_nr(pdev->bus);
> + id.pci.bus = pdev->bus->number;
> + id.pci.devfn = pdev->devfn;
> +
> + if (!device_to_iommu(id.pci.segment, id.pci.bus, id.pci.devfn))
> + return -ENODEV;
> +
> + bridge = pci_find_upstream_pcie_bridge(pdev);
> + if (bridge) {
> + if (pci_is_pcie(bridge)) {
> + id.pci.bus = bridge->subordinate->number;
> + id.pci.devfn = 0;
> + } else {
> + id.pci.bus = bridge->bus->number;
> + id.pci.devfn = bridge->devfn;
> + }
> + }
> +
> + /* Virtual functions always get their own group */
> + if (!pdev->is_virtfn && intel_iommu_no_mf_groups)
> + id.pci.devfn = PCI_DEVFN(PCI_SLOT(id.pci.devfn), 0);
> +
> + /* FIXME - seg # >= 0x8000 on 32b */
> + return id.group;
> +}

This looks like code duplication in the VT-d driver. It doesn't need to
be generalized now, but we should keep in mind to do a more general
solution later.
Maybe it is beneficial if the IOMMU drivers only setup the number in
dev->arch.iommu.groupid and the iommu-api fetches it from there then.
But as I said, this is some more work and does not need to be done for
this patch(-set).

> +
> static struct iommu_ops intel_iommu_ops = {
> .domain_init = intel_iommu_domain_init,
> .domain_destroy = intel_iommu_domain_destroy,
> @@ -3911,6 +3962,7 @@ static struct iommu_ops intel_iommu_ops = {
> .unmap = intel_iommu_unmap,
> .iova_to_phys = intel_iommu_iova_to_phys,
> .domain_has_cap = intel_iommu_domain_has_cap,
> + .dev_to_group = intel_iommu_dev_to_group,
> };
>
> static void __devinit quirk_iommu_rwbf(struct pci_dev *dev)
> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> index 0a2ba40..90c1a86 100644
> --- a/include/linux/iommu.h
> +++ b/include/linux/iommu.h
> @@ -45,6 +45,7 @@ struct iommu_ops {
> unsigned long iova);
> int (*domain_has_cap)(struct iommu_domain *domain,
> unsigned long cap);
> + long (*dev_to_group)(struct device *dev);
> };
>
> #ifdef CONFIG_IOMMU_API
> @@ -65,6 +66,7 @@ extern phys_addr_t iommu_iova_to_phys(struct iommu_domain *domain,
> unsigned long iova);
> extern int iommu_domain_has_cap(struct iommu_domain *domain,
> unsigned long cap);
> +extern long iommu_dev_to_group(struct device *dev);
>
> #else /* CONFIG_IOMMU_API */
>
> @@ -121,6 +123,10 @@ static inline int domain_has_cap(struct iommu_domain *domain,
> return 0;
> }
>
> +static inline long iommu_dev_to_group(struct device *dev);
> +{
> + return -ENODEV;
> +}
> #endif /* CONFIG_IOMMU_API */
>
> #endif /* __LINUX_IOMMU_H */
>
>
>

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