Subject: Re: kvm PCI assignment & VFIO ramblings

From: Don Dutile <[email-masked]>
Date: Thu, 25 Aug 2011 11:38:09 -0400

On 08/25/2011 06:54 AM, Roedel, Joerg wrote:
> 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.
>
When you think of a system where there isn't just one bus-type
with iommu support, it makes more sense.
Additionally, it also allows the long-term architecture to use different types
of IOMMUs on each bus segment -- think per-PCIe-switch/bridge IOMMUs --
esp. 'tuned' IOMMUs -- ones better geared for networks, ones better geared
for direct-attach disk hba's.

>>   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 */
>>
>>
>>
>