Subject: Re: kvm PCI assignment & VFIO ramblings

From: "Roedel, Joerg" <[email-masked]>
Date: Thu, 25 Aug 2011 12:54:02 +0200

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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