Date:   Mon, 14 May 2018 13:55:48 -0700
From:   Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     iommu@...ts.linux-foundation.org,
        LKML <linux-kernel@...r.kernel.org>,
        Joerg Roedel <joro@...tes.org>,
        David Woodhouse <dwmw2@...radead.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Jean-Philippe Brucker <jean-philippe.brucker@....com>,
        Rafael Wysocki <rafael.j.wysocki@...el.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        Raj Ashok <ashok.raj@...el.com>,
        Jean Delvare <khali@...ux-fr.org>,
        Christoph Hellwig <hch@...radead.org>,
        jacob.jun.pan@...ux.intel.com
Subject: Re: [PATCH v5 13/23] iommu: introduce device fault report API

On Mon, 14 May 2018 14:01:06 +0800
Lu Baolu <baolu.lu@...ux.intel.com> wrote:

> Hi,
> 
> On 05/12/2018 04:54 AM, Jacob Pan wrote:
> > Traditionally, device specific faults are detected and handled
> > within their own device drivers. When IOMMU is enabled, faults such
> > as DMA related transactions are detected by IOMMU. There is no
> > generic reporting mechanism to report faults back to the in-kernel
> > device driver or the guest OS in case of assigned devices.
> >
> > Faults detected by IOMMU is based on the transaction's source ID
> > which can be reported at per device basis, regardless of the device
> > type is a PCI device or not.
> >
> > The fault types include recoverable (e.g. page request) and
> > unrecoverable faults(e.g. access error). In most cases, faults can
> > be handled by IOMMU drivers internally. The primary use cases are as
> > follows:
> > 1. page request fault originated from an SVM capable device that is
> > assigned to guest via vIOMMU. In this case, the first level page
> > tables are owned by the guest. Page request must be propagated to
> > the guest to let guest OS fault in the pages then send page
> > response. In this mechanism, the direct receiver of IOMMU fault
> > notification is VFIO, which can relay notification events to QEMU
> > or other user space software.
> >
> > 2. faults need more subtle handling by device drivers. Other than
> > simply invoke reset function, there are needs to let device driver
> > handle the fault with a smaller impact.
> >
> > This patchset is intended to create a generic fault report API such
> > that it can scale as follows:
> > - all IOMMU types
> > - PCI and non-PCI devices
> > - recoverable and unrecoverable faults
> > - VFIO and other other in kernel users
> > - DMA & IRQ remapping (TBD)
> > The original idea was brought up by David Woodhouse and discussions
> > summarized at https://lwn.net/Articles/608914/.
> >
> > Signed-off-by: Jacob Pan <jacob.jun.pan@...ux.intel.com>
> > Signed-off-by: Ashok Raj <ashok.raj@...el.com>
> > Signed-off-by: Jean-Philippe Brucker <jean-philippe.brucker@....com>
> > ---
> >  drivers/iommu/iommu.c | 149
> > +++++++++++++++++++++++++++++++++++++++++++++++++-
> > include/linux/iommu.h |  35 +++++++++++- 2 files changed, 181
> > insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> > index 3a49b96..b3f9daf 100644
> > --- a/drivers/iommu/iommu.c
> > +++ b/drivers/iommu/iommu.c
> > @@ -609,6 +609,13 @@ int iommu_group_add_device(struct iommu_group
> > *group, struct device *dev) goto err_free_name;
> >  	}
> >  
> > +	dev->iommu_param = kzalloc(sizeof(*dev->iommu_param),
> > GFP_KERNEL);
> > +	if (!dev->iommu_param) {
> > +		ret = -ENOMEM;
> > +		goto err_free_name;
> > +	}
> > +	mutex_init(&dev->iommu_param->lock);
> > +
> >  	kobject_get(group->devices_kobj);
> >  
> >  	dev->iommu_group = group;
> > @@ -639,6 +646,7 @@ int iommu_group_add_device(struct iommu_group
> > *group, struct device *dev) mutex_unlock(&group->mutex);
> >  	dev->iommu_group = NULL;
> >  	kobject_put(group->devices_kobj);
> > +	kfree(dev->iommu_param);
> >  err_free_name:
> >  	kfree(device->name);
> >  err_remove_link:
> > @@ -685,7 +693,7 @@ void iommu_group_remove_device(struct device
> > *dev) sysfs_remove_link(&dev->kobj, "iommu_group");
> >  
> >  	trace_remove_device_from_group(group->id, dev);
> > -
> > +	kfree(dev->iommu_param);
> >  	kfree(device->name);
> >  	kfree(device);
> >  	dev->iommu_group = NULL;
> > @@ -820,6 +828,145 @@ int iommu_group_unregister_notifier(struct
> > iommu_group *group,
> > EXPORT_SYMBOL_GPL(iommu_group_unregister_notifier); 
> >  /**
> > + * iommu_register_device_fault_handler() - Register a device fault
> > handler
> > + * @dev: the device
> > + * @handler: the fault handler
> > + * @data: private data passed as argument to the handler
> > + *
> > + * When an IOMMU fault event is received, call this handler with
> > the fault event
> > + * and data as argument. The handler should return 0 on success.
> > If the fault is
> > + * recoverable (IOMMU_FAULT_PAGE_REQ), the handler can also
> > complete
> > + * the fault by calling iommu_page_response() with one of the
> > following
> > + * response code:
> > + * - IOMMU_PAGE_RESP_SUCCESS: retry the translation
> > + * - IOMMU_PAGE_RESP_INVALID: terminate the fault
> > + * - IOMMU_PAGE_RESP_FAILURE: terminate the fault and stop
> > reporting
> > + *   page faults if possible.
> > + *
> > + * Return 0 if the fault handler was installed successfully, or an
> > error.
> > + */
> > +int iommu_register_device_fault_handler(struct device *dev,
> > +					iommu_dev_fault_handler_t
> > handler,
> > +					void *data)
> > +{
> > +	struct iommu_param *param = dev->iommu_param;
> > +	int ret = 0;
> > +
> > +	/*
> > +	 * Device iommu_param should have been allocated when
> > device is
> > +	 * added to its iommu_group.
> > +	 */
> > +	if (!param)
> > +		return -EINVAL;
> > +
> > +	mutex_lock(&param->lock);
> > +	/* Only allow one fault handler registered for each device
> > */
> > +	if (param->fault_param) {
> > +		ret = -EBUSY;
> > +		goto done_unlock;
> > +	}
> > +
> > +	get_device(dev);
> > +	param->fault_param =
> > +		kzalloc(sizeof(struct iommu_fault_param),
> > GFP_KERNEL);
> > +	if (!param->fault_param) {
> > +		put_device(dev);
> > +		ret = -ENOMEM;
> > +		goto done_unlock;
> > +	}
> > +	mutex_init(&param->fault_param->lock);  
> 
> Do we really need this mutex lock? Is param->lock enough?
> 
I am trying to provide more fine locking granularity in that
iommu_param is meant to be expanded as the sole iommu data under struct
device, so the scope of param->lock may expand.
>  [...]  
> 
> Best regards,
> Lu Baolu

[Jacob Pan]

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