Re: [PATCH RESEND v5 4/5] iommu: Allow max opt DMA len be set for a group via sysfs

[John Garry via iommu <iommu@lists.linux-foundation.org>]

On 07/04/2022 09:21, Leizhen (ThunderTown) wrote:
> 
> 
> On 2022/4/4 19:27, John Garry wrote:
>> Add support to allow the maximum optimised DMA len be set for an IOMMU
>> group via sysfs.
>>
>> This is much the same with the method to change the default domain type
>> for a group.
>>
>> Signed-off-by: John Garry <john.garry@huawei.com>
>> ---
>>   .../ABI/testing/sysfs-kernel-iommu_groups     | 16 +++++
>>   drivers/iommu/iommu.c                         | 59 ++++++++++++++++++-
>>   include/linux/iommu.h                         |  6 ++
>>   3 files changed, 79 insertions(+), 2 deletions(-)
>>
>> diff --git a/Documentation/ABI/testing/sysfs-kernel-iommu_groups b/Documentation/ABI/testing/sysfs-kernel-iommu_groups
>> index b15af6a5bc08..ed6f72794f6c 100644
>> --- a/Documentation/ABI/testing/sysfs-kernel-iommu_groups
>> +++ b/Documentation/ABI/testing/sysfs-kernel-iommu_groups
>> @@ -63,3 +63,19 @@ Description:	/sys/kernel/iommu_groups/<grp_id>/type shows the type of default
>>   		system could lead to catastrophic effects (the users might
>>   		need to reboot the machine to get it to normal state). So, it's
>>   		expected that the users understand what they're doing.
>> +
>> +What:		/sys/kernel/iommu_groups/<grp_id>/max_opt_dma_size
>> +Date:		Feb 2022
>> +KernelVersion:	v5.18
>> +Contact:	iommu@lists.linux-foundation.org
>> +Description:	/sys/kernel/iommu_groups/<grp_id>/max_opt_dma_size shows the
>> +		max optimised DMA size for the default IOMMU domain associated
>> +		with the group.
>> +		Each IOMMU domain has an IOVA domain. The IOVA domain caches
>> +		IOVAs upto a certain size as a performance optimisation.
>> +		This sysfs file allows the range of the IOVA domain caching be
>> +		set, such that larger than default IOVAs may be cached.
>> +		A value of 0 means that the default caching range is chosen.
>> +		A privileged user could request the kernel the change the range
>> +		by writing to this file. For this to happen, the same rules
>> +		and procedure applies as in changing the default domain type.
>> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
>> index 10bb10c2a210..7c7258f19bed 100644
>> --- a/drivers/iommu/iommu.c
>> +++ b/drivers/iommu/iommu.c
>> @@ -48,6 +48,7 @@ struct iommu_group {
>>   	struct iommu_domain *default_domain;
>>   	struct iommu_domain *domain;
>>   	struct list_head entry;
>> +	size_t max_opt_dma_size;
>>   };
>>   
>>   struct group_device {
>> @@ -89,6 +90,9 @@ static int iommu_create_device_direct_mappings(struct iommu_group *group,
>>   static struct iommu_group *iommu_group_get_for_dev(struct device *dev);
>>   static ssize_t iommu_group_store_type(struct iommu_group *group,
>>   				      const char *buf, size_t count);
>> +static ssize_t iommu_group_store_max_opt_dma_size(struct iommu_group *group,
>> +						  const char *buf,
>> +						  size_t count);
>>   
>>   #define IOMMU_GROUP_ATTR(_name, _mode, _show, _store)		\
>>   struct iommu_group_attribute iommu_group_attr_##_name =		\
>> @@ -571,6 +575,12 @@ static ssize_t iommu_group_show_type(struct iommu_group *group,
>>   	return strlen(type);
>>   }
>>   
>> +static ssize_t iommu_group_show_max_opt_dma_size(struct iommu_group *group,
>> +				     char *buf)
>> +{
>> +	return sprintf(buf, "%zu\n", group->max_opt_dma_size);
>> +}
>> +
>>   static IOMMU_GROUP_ATTR(name, S_IRUGO, iommu_group_show_name, NULL);
>>   
>>   static IOMMU_GROUP_ATTR(reserved_regions, 0444,
>> @@ -579,6 +589,9 @@ static IOMMU_GROUP_ATTR(reserved_regions, 0444,
>>   static IOMMU_GROUP_ATTR(type, 0644, iommu_group_show_type,
>>   			iommu_group_store_type);
>>   
>> +static IOMMU_GROUP_ATTR(max_opt_dma_size, 0644, iommu_group_show_max_opt_dma_size,
>> +			iommu_group_store_max_opt_dma_size);
>> +
>>   static void iommu_group_release(struct kobject *kobj)
>>   {
>>   	struct iommu_group *group = to_iommu_group(kobj);
>> @@ -665,6 +678,10 @@ struct iommu_group *iommu_group_alloc(void)
>>   	if (ret)
>>   		return ERR_PTR(ret);
>>   
>> +	ret = iommu_group_create_file(group, &iommu_group_attr_max_opt_dma_size);
>> +	if (ret)
>> +		return ERR_PTR(ret);
>> +
>>   	pr_debug("Allocated group %d\n", group->id);
>>   
>>   	return group;
>> @@ -2087,6 +2104,11 @@ struct iommu_domain *iommu_get_dma_domain(struct device *dev)
>>   	return dev->iommu_group->default_domain;
>>   }
>>   
>> +size_t iommu_group_get_max_opt_dma_size(struct iommu_group *group)
>> +{
>> +	return group->max_opt_dma_size;
>> +}
>> +
>>   /*
>>    * IOMMU groups are really the natural working unit of the IOMMU, but
>>    * the IOMMU API works on domains and devices.  Bridge that gap by
>> @@ -2871,12 +2893,14 @@ EXPORT_SYMBOL_GPL(iommu_sva_get_pasid);
>>    * @prev_dev: The device in the group (this is used to make sure that the device
>>    *	 hasn't changed after the caller has called this function)
>>    * @type: The type of the new default domain that gets associated with the group
>> + * @max_opt_dma_size: Set the IOMMU group max_opt_dma_size if non-zero
>>    *
>>    * Returns 0 on success and error code on failure
>>    *
>>    */
>>   static int iommu_change_dev_def_domain(struct iommu_group *group,
>> -				       struct device *prev_dev, int type)
>> +				       struct device *prev_dev, int type,
>> +				       unsigned long max_opt_dma_size)
>>   {
>>   	struct iommu_domain *prev_dom;
>>   	struct group_device *grp_dev;
>> @@ -2977,6 +3001,9 @@ static int iommu_change_dev_def_domain(struct iommu_group *group,
>>   
>>   	group->domain = group->default_domain;
>>   
>> +	if (max_opt_dma_size)
>> +		group->max_opt_dma_size = max_opt_dma_size;
> 

Hi Leizhen,

> Why not add a new function just do this?

But how would the function look?

> In this way, we do not need to modify
> iommu_change_dev_def_domain() and patch 3/5 can be dropped.

A change in the group max_opt_dma_size will only be applied when realloc 
the def domain, i.e. in this function, and we need 3/5 to support that

thanks,
John

> 
>> +
>>   	/*
>>   	 * Release the mutex here because ops->probe_finalize() call-back of
>>   	 * some vendor IOMMU drivers calls arm_iommu_attach_device() which
>> @@ -3003,6 +3030,7 @@ static int iommu_change_dev_def_domain(struct iommu_group *group,
>>   
>>   enum iommu_group_op {
>>   	CHANGE_GROUP_TYPE,
>> +	CHANGE_DMA_OPT_SIZE,
>>   };
>>   
>>   static int __iommu_group_store_type(const char *buf, struct iommu_group *group,
>> @@ -3031,7 +3059,24 @@ static int __iommu_group_store_type(const char *buf, struct iommu_group *group,
>>   		return -EINVAL;
>>   	}
>>   
>> -	return iommu_change_dev_def_domain(group, dev, type);
>> +	return iommu_change_dev_def_domain(group, dev, type, 0);
>> +}
>> +
>> +static int __iommu_group_store_max_opt_dma_size(const char *buf,
>> +						struct iommu_group *group,
>> +						struct device *dev)
>> +{
>> +	unsigned long val;
>> +
>> +	if (kstrtoul(buf, 0, &val) || !val)
>> +		return -EINVAL;
>> +
>> +	if (device_is_bound(dev)) {
>> +		pr_err_ratelimited("Device is still bound to driver\n");
>> +		return -EINVAL;
>> +	}
>> +
>> +	return iommu_change_dev_def_domain(group, dev, __IOMMU_DOMAIN_SAME, val);
>>   }
>>   
>>   /*
>> @@ -3108,6 +3153,9 @@ static ssize_t iommu_group_store_common(struct iommu_group *group,
>>   	case CHANGE_GROUP_TYPE:
>>   		ret = __iommu_group_store_type(buf, group, dev);
>>   		break;
>> +	case CHANGE_DMA_OPT_SIZE:
>> +		ret = __iommu_group_store_max_opt_dma_size(buf, group, dev);
>> +		break;
>>   	default:
>>   		ret = -EINVAL;
>>   	}
>> @@ -3124,3 +3172,10 @@ static ssize_t iommu_group_store_type(struct iommu_group *group,
>>   {
>>   	return iommu_group_store_common(group, CHANGE_GROUP_TYPE, buf, count);
>>   }
>> +
>> +static ssize_t iommu_group_store_max_opt_dma_size(struct iommu_group *group,
>> +						  const char *buf,
>> +						  size_t count)
>> +{
>> +	return iommu_group_store_common(group, CHANGE_DMA_OPT_SIZE, buf, count);
>> +}
>> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
>> index b141cf71c7af..6915e68c40b7 100644
>> --- a/include/linux/iommu.h
>> +++ b/include/linux/iommu.h
>> @@ -430,6 +430,7 @@ extern int iommu_sva_unbind_gpasid(struct iommu_domain *domain,
>>   				   struct device *dev, ioasid_t pasid);
>>   extern struct iommu_domain *iommu_get_domain_for_dev(struct device *dev);
>>   extern struct iommu_domain *iommu_get_dma_domain(struct device *dev);
>> +extern size_t iommu_group_get_max_opt_dma_size(struct iommu_group *group);
>>   extern int iommu_map(struct iommu_domain *domain, unsigned long iova,
>>   		     phys_addr_t paddr, size_t size, int prot);
>>   extern int iommu_map_atomic(struct iommu_domain *domain, unsigned long iova,
>> @@ -725,6 +726,11 @@ static inline struct iommu_domain *iommu_get_domain_for_dev(struct device *dev)
>>   	return NULL;
>>   }
>>   
>> +static inline size_t iommu_group_get_max_opt_dma_size(struct iommu_group *group)
>> +{
>> +	return 0;
>> +}
>> +
>>   static inline int iommu_map(struct iommu_domain *domain, unsigned long iova,
>>   			    phys_addr_t paddr, size_t size, int prot)
>>   {
>>
> 

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