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From: Shameerali Kolothum Thodi <shameerali.kolothum.thodi@huawei.com>
To: Ashok Raj <ashok.raj@intel.com>, Joerg Roedel <joro@8bytes.org>,
	"iommu@lists.linux-foundation.org"
	<iommu@lists.linux-foundation.org>,
	"baolu.lu@linux.intel.com" <baolu.lu@linux.intel.com>
Cc: Robin Murphy <robin.murphy@arm.com>,
	Will Deacon <will.deacon@arm.com>, Christoph Hellwig <hch@lst.de>
Subject: RE: [Patch V8 1/3] iommu: Add support to change default domain of an iommu group
Date: Fri, 20 Nov 2020 11:27:17 +0000	[thread overview]
Message-ID: <243ce89c33fe4b9da4c56ba35acebf81@huawei.com> (raw)
In-Reply-To: <20200925190620.18732-2-ashok.raj@intel.com>

Hi Baolu/Ashok,

> -----Original Message-----
> From: iommu [mailto:iommu-bounces@lists.linux-foundation.org] On Behalf Of
> Ashok Raj
> Sent: 25 September 2020 20:06
> To: Joerg Roedel <joro@8bytes.org>; iommu@lists.linux-foundation.org
> Cc: Ashok Raj <ashok.raj@intel.com>; Will Deacon <will.deacon@arm.com>;
> Robin Murphy <robin.murphy@arm.com>; Christoph Hellwig <hch@lst.de>
> Subject: [Patch V8 1/3] iommu: Add support to change default domain of an
> iommu group
> 
> From: Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>
> 
> Presently, the default domain of an iommu group is allocated during boot
> time and it cannot be changed later. So, the device would typically be
> either in identity (also known as pass_through) mode or the device would be
> in DMA mode as long as the machine is up and running. There is no way to
> change the default domain type dynamically i.e. after booting, a device
> cannot switch between identity mode and DMA mode.
> 
> But, assume a use case wherein the user trusts the device and believes that
> the OS is secure enough and hence wants *only* this device to bypass IOMMU
> (so that it could be high performing) whereas all the other devices to go
> through IOMMU (so that the system is protected). Presently, this use case
> is not supported. It will be helpful if there is some way to change the
> default domain of an iommu group dynamically. Hence, add such support.
> 
> A privileged user could request the kernel to change the default domain
> type of a iommu group by writing to
> "/sys/kernel/iommu_groups/<grp_id>/type" file. Presently, only three values
> are supported
> 1. identity: all the DMA transactions from the device in this group are
>              *not* translated by the iommu
> 2. DMA: all the DMA transactions from the device in this group are
>         translated by the iommu
> 3. auto: change to the type the device was booted with
> 
> Note:
> 1. Default domain of an iommu group with two or more devices cannot be
>    changed.
> 2. The device in the iommu group shouldn't be bound to any driver.
> 3. The device shouldn't be assigned to user for direct access.
> 4. The vendor iommu driver is required to add def_domain_type() callback.
>    The change request will fail if the request type conflicts with that
>    returned from the callback.

Currently Arm SMMUv3 driver doesn't provide the def_doman_type() callback.
And I have sent a patch[1] based on this series to just add that. But Robin made
couple of suggestions there which can be incorporated into this series so that the
vendor driver no more required to provide the callback for this feature to work. 

1. Include a generic checking for 
	if (dev_is_pci(dev)) {
		if (pci_dev->untrusted)
			return IOMMU_DOMAIN_DMA;
	}

2. Also if there is no def_doman_type() callback provided by vendor driver, assume
  that the dev supports both IDENTITY and DMA domain types.

If you plan to respin this series, could you please consider the above as well?
Please let me know.

Thanks,
Shameer

1. https://lore.kernel.org/linux-iommu/a3c73596-70d9-4204-d598-5e6684868544@arm.com/

> Please see "Documentation/ABI/testing/sysfs-kernel-iommu_groups" for more
> information.
> 
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Joerg Roedel <joro@8bytes.org>
> Cc: Ashok Raj <ashok.raj@intel.com>
> Cc: Will Deacon <will.deacon@arm.com>
> Cc: Lu Baolu <baolu.lu@linux.intel.com>
> Cc: Sohil Mehta <sohil.mehta@intel.com>
> Cc: Robin Murphy <robin.murphy@arm.com>
> Cc: Jacob Pan <jacob.jun.pan@linux.intel.com>
> Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>
> Signed-off-by: Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>
> ---
>  drivers/iommu/iommu.c | 225
> +++++++++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 224 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index 6c14c88cd525..2e93c48ce248 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -93,6 +93,8 @@ static void __iommu_detach_group(struct
> iommu_domain *domain,
>  static int iommu_create_device_direct_mappings(struct iommu_group
> *group,
>  					       struct device *dev);
>  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);
> 
>  #define IOMMU_GROUP_ATTR(_name, _mode, _show, _store)		\
>  struct iommu_group_attribute iommu_group_attr_##_name =		\
> @@ -525,7 +527,8 @@ static IOMMU_GROUP_ATTR(name, S_IRUGO,
> iommu_group_show_name, NULL);
>  static IOMMU_GROUP_ATTR(reserved_regions, 0444,
>  			iommu_group_show_resv_regions, NULL);
> 
> -static IOMMU_GROUP_ATTR(type, 0444, iommu_group_show_type, NULL);
> +static IOMMU_GROUP_ATTR(type, 0644, iommu_group_show_type,
> +			iommu_group_store_type);
> 
>  static void iommu_group_release(struct kobject *kobj)
>  {
> @@ -2849,3 +2852,223 @@ int iommu_sva_get_pasid(struct iommu_sva
> *handle)
>  	return ops->sva_get_pasid(handle);
>  }
>  EXPORT_SYMBOL_GPL(iommu_sva_get_pasid);
> +
> +/*
> + * Changes the default domain of an iommu group that has *only* one device
> + *
> + * @group: The group for which the default domain should be changed
> + * @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
> + *
> + * Returns 0 on success and error code on failure
> + *
> + * Note:
> + * 1. Presently, this function is called only when user requests to change the
> + *    group's default domain type through
> /sys/kernel/iommu_groups/<grp_id>/type
> + *    Please take a closer look if intended to use for other purposes.
> + */
> +static int iommu_change_dev_def_domain(struct iommu_group *group,
> +				       struct device *prev_dev, int type)
> +{
> +	struct iommu_domain *prev_dom;
> +	struct group_device *grp_dev;
> +	const struct iommu_ops *ops;
> +	int ret, dev_def_dom;
> +	struct device *dev;
> +
> +	if (!group)
> +		return -EINVAL;
> +
> +	mutex_lock(&group->mutex);
> +
> +	if (group->default_domain != group->domain) {
> +		pr_err_ratelimited("Group not assigned to default domain\n");
> +		ret = -EBUSY;
> +		goto out;
> +	}
> +
> +	/*
> +	 * iommu group wasn't locked while acquiring device lock in
> +	 * iommu_group_store_type(). So, make sure that the device count hasn't
> +	 * changed while acquiring device lock.
> +	 *
> +	 * Changing default domain of an iommu group with two or more devices
> +	 * isn't supported because there could be a potential deadlock. Consider
> +	 * the following scenario. T1 is trying to acquire device locks of all
> +	 * the devices in the group and before it could acquire all of them,
> +	 * there could be another thread T2 (from different sub-system and use
> +	 * case) that has already acquired some of the device locks and might be
> +	 * waiting for T1 to release other device locks.
> +	 */
> +	if (iommu_group_device_count(group) != 1) {
> +		pr_err_ratelimited("Cannot change default domain: Group has more
> than one device\n");
> +		ret = -EINVAL;
> +		goto out;
> +	}
> +
> +	/* Since group has only one device */
> +	grp_dev = list_first_entry(&group->devices, struct group_device, list);
> +	dev = grp_dev->dev;
> +
> +	if (prev_dev != dev) {
> +		pr_err_ratelimited("Cannot change default domain: Device has been
> changed\n");
> +		ret = -EBUSY;
> +		goto out;
> +	}
> +
> +	prev_dom = group->default_domain;
> +	if (!prev_dom || !prev_dom->ops || !prev_dom->ops->def_domain_type) {
> +		ret = -EINVAL;
> +		goto out;
> +	}
> +
> +	ops = prev_dom->ops;
> +	dev_def_dom = ops->def_domain_type(dev);
> +
> +	/* Check if user requested domain is supported by the device or not */
> +	if (!type) {
> +		/*
> +		 * If the user hasn't requested any specific type of domain and
> +		 * if the device supports both the domains, then default to the
> +		 * domain the device was booted with
> +		 */
> +		type = dev_def_dom ?: iommu_def_domain_type;
> +	} else if (dev_def_dom && type != dev_def_dom) {
> +		pr_err_ratelimited("Device cannot be in %s domain\n",
> +				   iommu_domain_type_str(type));
> +		ret = -EINVAL;
> +		goto out;
> +	}
> +
> +	/*
> +	 * Switch to a new domain only if the requested domain type is different
> +	 * from the existing default domain type
> +	 */
> +	if (prev_dom->type == type) {
> +		ret = 0;
> +		goto out;
> +	}
> +
> +	/* Sets group->default_domain to the newly allocated domain */
> +	ret = iommu_group_alloc_default_domain(dev->bus, group, type);
> +	if (ret)
> +		goto out;
> +
> +	ret = iommu_create_device_direct_mappings(group, dev);
> +	if (ret)
> +		goto free_new_domain;
> +
> +	ret = __iommu_attach_device(group->default_domain, dev);
> +	if (ret)
> +		goto free_new_domain;
> +
> +	group->domain = group->default_domain;
> +
> +	/*
> +	 * Release the mutex here because ops->probe_finalize() call-back of
> +	 * some vendor IOMMU drivers calls arm_iommu_attach_device() which
> +	 * in-turn might call back into IOMMU core code, where it tries to take
> +	 * group->mutex, resulting in a deadlock.
> +	 */
> +	mutex_unlock(&group->mutex);
> +
> +	/* Make sure dma_ops is appropriatley set */
> +	iommu_group_do_probe_finalize(dev, group->default_domain);
> +	iommu_domain_free(prev_dom);
> +	return 0;
> +
> +free_new_domain:
> +	iommu_domain_free(group->default_domain);
> +	group->default_domain = prev_dom;
> +	group->domain = prev_dom;
> +
> +out:
> +	mutex_unlock(&group->mutex);
> +
> +	return ret;
> +}
> +
> +static ssize_t iommu_group_store_type(struct iommu_group *group,
> +				      const char *buf, size_t count)
> +{
> +	struct group_device *grp_dev;
> +	struct device *dev;
> +	int ret, req_type;
> +
> +	if (!capable(CAP_SYS_ADMIN) || !capable(CAP_SYS_RAWIO))
> +		return -EACCES;
> +
> +	if (WARN_ON(!group))
> +		return -EINVAL;
> +
> +	if (sysfs_streq(buf, "identity"))
> +		req_type = IOMMU_DOMAIN_IDENTITY;
> +	else if (sysfs_streq(buf, "DMA"))
> +		req_type = IOMMU_DOMAIN_DMA;
> +	else if (sysfs_streq(buf, "auto"))
> +		req_type = 0;
> +	else
> +		return -EINVAL;
> +
> +	/*
> +	 * Lock/Unlock the group mutex here before device lock to
> +	 * 1. Make sure that the iommu group has only one device (this is a
> +	 *    prerequisite for step 2)
> +	 * 2. Get struct *dev which is needed to lock device
> +	 */
> +	mutex_lock(&group->mutex);
> +	if (iommu_group_device_count(group) != 1) {
> +		mutex_unlock(&group->mutex);
> +		pr_err_ratelimited("Cannot change default domain: Group has more
> than one device\n");
> +		return -EINVAL;
> +	}
> +
> +	/* Since group has only one device */
> +	grp_dev = list_first_entry(&group->devices, struct group_device, list);
> +	dev = grp_dev->dev;
> +	get_device(dev);
> +
> +	/*
> +	 * Don't hold the group mutex because taking group mutex first and then
> +	 * the device lock could potentially cause a deadlock as below. Assume
> +	 * two threads T1 and T2. T1 is trying to change default domain of an
> +	 * iommu group and T2 is trying to hot unplug a device or release [1] VF
> +	 * of a PCIe device which is in the same iommu group. T1 takes group
> +	 * mutex and before it could take device lock assume T2 has taken device
> +	 * lock and is yet to take group mutex. Now, both the threads will be
> +	 * waiting for the other thread to release lock. Below, lock order was
> +	 * suggested.
> +	 * device_lock(dev);
> +	 *	mutex_lock(&group->mutex);
> +	 *		iommu_change_dev_def_domain();
> +	 *	mutex_unlock(&group->mutex);
> +	 * device_unlock(dev);
> +	 *
> +	 * [1] Typical device release path
> +	 * device_lock() from device/driver core code
> +	 *  -> bus_notifier()
> +	 *   -> iommu_bus_notifier()
> +	 *    -> iommu_release_device()
> +	 *     -> ops->release_device() vendor driver calls back iommu core
> code
> +	 *      -> mutex_lock() from iommu core code
> +	 */
> +	mutex_unlock(&group->mutex);
> +
> +	/* Check if the device in the group still has a driver bound to it */
> +	device_lock(dev);
> +	if (device_is_bound(dev)) {
> +		pr_err_ratelimited("Device is still bound to driver\n");
> +		ret = -EBUSY;
> +		goto out;
> +	}
> +
> +	ret = iommu_change_dev_def_domain(group, dev, req_type);
> +	ret = ret ?: count;
> +
> +out:
> +	device_unlock(dev);
> +	put_device(dev);
> +
> +	return ret;
> +}
> --
> 2.7.4
> 
> _______________________________________________
> iommu mailing list
> iommu@lists.linux-foundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/iommu
_______________________________________________
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  parent reply	other threads:[~2020-11-20 11:27 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-25 19:06 [Patch V8 0/3] " Ashok Raj
2020-09-25 19:06 ` [Patch V8 1/3] " Ashok Raj
2020-11-18 13:51   ` Will Deacon
2020-11-19  2:18     ` Lu Baolu
2020-11-19  8:53       ` Will Deacon
2020-11-20  2:11         ` Lu Baolu
2020-11-20 11:03           ` Will Deacon
2020-11-20 11:27   ` Shameerali Kolothum Thodi [this message]
2020-11-20 13:09     ` Lu Baolu
2020-09-25 19:06 ` [Patch V8 2/3] iommu: Take lock before reading iommu group default domain type Ashok Raj
2020-09-25 19:06 ` [Patch V8 3/3] iommu: Document usage of "/sys/kernel/iommu_groups/<grp_id>/type" file Ashok Raj
2020-11-18 13:51   ` Will Deacon
2020-11-19  2:32     ` Lu Baolu
2020-11-19  8:55       ` Will Deacon
2020-11-20  2:13         ` Lu Baolu
2020-10-01 12:58 ` [Patch V8 0/3] iommu: Add support to change default domain of an iommu group Joerg Roedel
2020-10-01 13:51   ` Raj, Ashok
2020-11-18 13:52 ` Will Deacon
2020-11-19  2:36   ` Lu Baolu

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