Re: [PATCH kernel 3/3] powerpc/iommu: Add iommu_ops to report capabilities and allow blocking domains

[Alexey Kardashevskiy <aik@ozlabs.ru>]

On 19/07/2022 04:09, Jason Gunthorpe wrote:
> On Thu, Jul 14, 2022 at 06:18:22PM +1000, Alexey Kardashevskiy wrote:
> 
>> +/*
>> + * A simple iommu_ops to allow less cruft in generic VFIO code.
>> + */
>> +static bool spapr_tce_iommu_capable(enum iommu_cap cap)
>> +{
>> +	switch (cap) {
>> +	case IOMMU_CAP_CACHE_COHERENCY:
> 
> I would add a remark here that it is because vfio is going to use
> SPAPR mode but still checks that the iommu driver support coherency -
> with out that detail it looks very strange to have caps without
> implementing unmanaged domains
> 
>> +static struct iommu_domain *spapr_tce_iommu_domain_alloc(unsigned int type)
>> +{
>> +	struct iommu_domain *dom;
>> +
>> +	if (type != IOMMU_DOMAIN_BLOCKED)
>> +		return NULL;
>> +
>> +	dom = kzalloc(sizeof(*dom), GFP_KERNEL);
>> +	if (!dom)
>> +		return NULL;
>> +
>> +	dom->geometry.aperture_start = 0;
>> +	dom->geometry.aperture_end = ~0ULL;
>> +	dom->geometry.force_aperture = true;
> 
> A blocked domain doesn't really have an aperture, all DMA is rejected,
> so I think these can just be deleted and left at zero.
> 
> Generally I'm suggesting drivers just use a static singleton instance
> for the blocked domain instead of the allocation like this, but that
> is a very minor nit.
> 
>> +static struct iommu_device *spapr_tce_iommu_probe_device(struct device *dev)
>> +{
>> +	struct pci_dev *pdev;
>> +	struct pci_controller *hose;
>> +
>> +	/* Weirdly iommu_device_register() assigns the same ops to all buses */
>> +	if (!dev_is_pci(dev))
>> +		return ERR_PTR(-EPERM);
> 
> Less "weirdly", more by design. The iommu driver should check if the
> given struct device is supported or not, it isn't really a bus
> specific operation.
> 
>> +static struct iommu_group *spapr_tce_iommu_device_group(struct device *dev)
>> +{
>> +	struct pci_controller *hose;
>> +	struct pci_dev *pdev;
>> +
>> +	/* Weirdly iommu_device_register() assigns the same ops to all buses */
>> +	if (!dev_is_pci(dev))
>> +		return ERR_PTR(-EPERM);
> 
> This doesn't need repeating, if probe_device() fails then this will
> never be called.
> 
>> +static int spapr_tce_iommu_attach_dev(struct iommu_domain *dom,
>> +				      struct device *dev)
>> +{
>> +	struct iommu_group *grp = iommu_group_get(dev);
>> +	struct iommu_table_group *table_group;
>> +	int ret = -EINVAL;
>> +
>> +	if (!grp)
>> +		return -ENODEV;
>> +
>> +	table_group = iommu_group_get_iommudata(grp);
>> +
>> +	if (dom->type == IOMMU_DOMAIN_BLOCKED)
>> +		ret = table_group->ops->take_ownership(table_group);
> 
> Ideally there shouldn't be dom->type checks like this.
> 
> 
> The blocking domain should have its own iommu_domain_ops that only
> process the blocking operation. Ie call this like
> spapr_tce_iommu_blocking_attach_dev()
> 
> Instead of having a "default_domain_ops" leave it NULL and create a
> spapr_tce_blocking_domain_ops with these two functions and assign it
> to domain->ops when creating. Then it is really clear these functions
> are only called for the DOMAIN_BLOCKED type and you don't need to
> check it.
> 
>> +static void spapr_tce_iommu_detach_dev(struct iommu_domain *dom,
>> +				       struct device *dev)
>> +{
>> +	struct iommu_group *grp = iommu_group_get(dev);
>> +	struct iommu_table_group *table_group;
>> +
>> +	table_group = iommu_group_get_iommudata(grp);
>> +	WARN_ON(dom->type != IOMMU_DOMAIN_BLOCKED);
>> +	table_group->ops->release_ownership(table_group);
>> +}
> 
> Ditto
> 
>> +struct iommu_group *pSeries_pci_device_group(struct pci_controller *hose,
>> +					     struct pci_dev *pdev)
>> +{
>> +	struct device_node *pdn, *dn = pdev->dev.of_node;
>> +	struct iommu_group *grp;
>> +	struct pci_dn *pci;
>> +
>> +	pdn = pci_dma_find(dn, NULL);
>> +	if (!pdn || !PCI_DN(pdn))
>> +		return ERR_PTR(-ENODEV);
>> +
>> +	pci = PCI_DN(pdn);
>> +	if (!pci->table_group)
>> +		return ERR_PTR(-ENODEV);
>> +
>> +	grp = pci->table_group->group;
>> +	if (!grp)
>> +		return ERR_PTR(-ENODEV);
>> +
>> +	return iommu_group_ref_get(grp);
> 
> Not for this series, but this is kind of backwards, the driver
> specific data (ie the table_group) should be in
> iommu_group_get_iommudata()...


It is there but here we are getting from a device to a group - a device 
is not added to a group yet when iommu_probe_device() works and tries 
adding a device via iommu_group_get_for_dev().




>> diff --git a/drivers/vfio/vfio_iommu_spapr_tce.c b/drivers/vfio/vfio_iommu_spapr_tce.c
>> index 8a65ea61744c..3b53b466e49b 100644
>> --- a/drivers/vfio/vfio_iommu_spapr_tce.c
>> +++ b/drivers/vfio/vfio_iommu_spapr_tce.c
>> @@ -1152,8 +1152,6 @@ static void tce_iommu_release_ownership(struct tce_container *container,
>>   	for (i = 0; i < IOMMU_TABLE_GROUP_MAX_TABLES; ++i)
>>   		if (container->tables[i])
>>   			table_group->ops->unset_window(table_group, i);
>> -
>> -	table_group->ops->release_ownership(table_group);
>>   }
>>   
>>   static long tce_iommu_take_ownership(struct tce_container *container,
>> @@ -1161,10 +1159,6 @@ static long tce_iommu_take_ownership(struct tce_container *container,
>>   {
>>   	long i, ret = 0;
>>   
>> -	ret = table_group->ops->take_ownership(table_group);
>> -	if (ret)
>> -		return ret;
>> -
>>   	/* Set all windows to the new group */
>>   	for (i = 0; i < IOMMU_TABLE_GROUP_MAX_TABLES; ++i) {
>>   		struct iommu_table *tbl = container->tables[i];
>> @@ -1183,8 +1177,6 @@ static long tce_iommu_take_ownership(struct tce_container *container,
>>   	for (i = 0; i < IOMMU_TABLE_GROUP_MAX_TABLES; ++i)
>>   		table_group->ops->unset_window(table_group, i);
>>   
>> -	table_group->ops->release_ownership(table_group);
>> -
> 
> This is great, makes alot of sense.
> 
> Anyhow, it all looks fine to me as is even:
> 
> Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>

Thanks. I'll try now to find an interested party to test this :)


> 
> Jason

-- 
Alexey