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Subject: Re: [PATCH RESEND v5 4/5] iommu: Allow max opt DMA len be set for a
 group via sysfs
To:     John Garry <john.garry@huawei.com>, <joro@8bytes.org>,
        <will@kernel.org>, <robin.murphy@arm.com>
CC:     <mst@redhat.com>, <jasowang@redhat.com>,
        <iommu@lists.linux-foundation.org>, <linux-kernel@vger.kernel.org>,
        <virtualization@lists.linux-foundation.org>,
        <chenxiang66@hisilicon.com>, <jean-philippe@linaro.org>,
        <linuxarm@huawei.com>
References: <1649071634-188535-1-git-send-email-john.garry@huawei.com>
 <1649071634-188535-5-git-send-email-john.garry@huawei.com>
From:   "Leizhen (ThunderTown)" <thunder.leizhen@huawei.com>
Message-ID: <19d075d7-fa4b-1ee5-2045-73cdaadc5929@huawei.com>
Date:   Thu, 7 Apr 2022 16:21:17 +0800
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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;

Why not add a new function just do this? In this way, we do not need to modify
iommu_change_dev_def_domain() and patch 3/5 can be dropped.

> +
>  	/*
>  	 * 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)
>  {
> 

-- 
Regards,
  Zhen Lei