Re: [PATCH v2] vfio/pci: Support error recovery

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Jan 10, 2017 at 07:46:17PM +0800, Cao jin wrote:
> 
> 
> On 01/10/2017 07:04 AM, Michael S. Tsirkin wrote:
> > On Sat, Dec 31, 2016 at 05:15:36PM +0800, Cao jin wrote:
> >> Support serious device error recovery
> > 
> > serious?
> >
> 
> Sorry for my poor vocabulary if it confuses people. I wanted to express
> the meaning that: vfio-pci actually cannot do a real recovery for device
> even if it provides the callbacks, it relies on the user to do a
> effective(or word "serious"?) recovery.
> 
> Welcome the amendment on the commit log.

It's up to Alex, maybe he's able to figure it all out from
code, but the rest of us could benefit from a description
of what the patch does from userspace point of view.

Also, is it a pre-requisite of the userspace patches you posted?

> -- 
> Sincerely,
> Cao jin
> 
> >>
> >> Signed-off-by: Cao jin <caoj.fnst@cn.fujitsu.com>
> >> ---
> >>  drivers/vfio/pci/vfio_pci.c         | 70 +++++++++++++++++++++++++++++++++++--
> >>  drivers/vfio/pci/vfio_pci_private.h |  2 ++
> >>  2 files changed, 70 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
> >> index 712a849..752af20 100644
> >> --- a/drivers/vfio/pci/vfio_pci.c
> >> +++ b/drivers/vfio/pci/vfio_pci.c
> >> @@ -534,6 +534,15 @@ static long vfio_pci_ioctl(void *device_data,
> >>  {
> >>  	struct vfio_pci_device *vdev = device_data;
> >>  	unsigned long minsz;
> >> +	int ret;
> >> +
> >> +	if (vdev->aer_recovering && (cmd == VFIO_DEVICE_SET_IRQS ||
> >> +	    cmd == VFIO_DEVICE_RESET || cmd == VFIO_DEVICE_PCI_HOT_RESET)) {
> >> +		ret = wait_for_completion_interruptible(
> >> +			&vdev->aer_completion);
> > 
> > don't split it like that.
> > 
> >> +		if (ret)
> >> +			return ret;
> >> +	}
> >>  
> >>  	if (cmd == VFIO_DEVICE_GET_INFO) {
> >>  		struct vfio_device_info info;
> >> @@ -953,6 +962,15 @@ static ssize_t vfio_pci_rw(void *device_data, char __user *buf,
> >>  {
> >>  	unsigned int index = VFIO_PCI_OFFSET_TO_INDEX(*ppos);
> >>  	struct vfio_pci_device *vdev = device_data;
> >> +	int ret;
> >> +
> >> +	/* block all kinds of access during host recovery */
> >> +	if (vdev->aer_recovering) {
> >> +		ret = wait_for_completion_interruptible(
> >> +			&vdev->aer_completion);
> >> +		if (ret)
> >> +			return ret;
> >> +	}
> >>  
> >>  	if (index >= VFIO_PCI_NUM_REGIONS + vdev->num_regions)
> >>  		return -EINVAL;
> >> @@ -1117,6 +1135,7 @@ static int vfio_pci_probe(struct pci_dev *pdev, const struct pci_device_id *id)
> >>  	vdev->irq_type = VFIO_PCI_NUM_IRQS;
> >>  	mutex_init(&vdev->igate);
> >>  	spin_lock_init(&vdev->irqlock);
> >> +	init_completion(&vdev->aer_completion);
> >>  
> >>  	ret = vfio_add_group_dev(&pdev->dev, &vfio_pci_ops, vdev);
> >>  	if (ret) {
> >> @@ -1176,6 +1195,9 @@ static pci_ers_result_t vfio_pci_aer_err_detected(struct pci_dev *pdev,
> >>  {
> >>  	struct vfio_pci_device *vdev;
> >>  	struct vfio_device *device;
> >> +	u32 uncor_status;
> >> +	unsigned int aer_cap_offset;
> >> +	int ret;
> >>  
> >>  	device = vfio_device_get_from_dev(&pdev->dev);
> >>  	if (device == NULL)
> >> @@ -1187,10 +1209,29 @@ static pci_ers_result_t vfio_pci_aer_err_detected(struct pci_dev *pdev,
> >>  		return PCI_ERS_RESULT_DISCONNECT;
> >>  	}
> >>  
> >> +	/*
> >> +	 * get device's uncorrectable error status as soon as possible,
> > 
> > should be "Get".
> > 
> >> +	 * and signal it to user space. The later we read it, the possibility
> >> +	 * the register value is mangled grows.
> >> +	 */
> >> +	aer_cap_offset = pci_find_ext_capability(vdev->pdev, PCI_EXT_CAP_ID_ERR);
> >> +	ret = pci_read_config_dword(vdev->pdev, aer_cap_offset +
> >> +                                    PCI_ERR_UNCOR_STATUS, &uncor_status);
> >> +        if (ret)
> >> +                return PCI_ERS_RESULT_DISCONNECT;
> >> +
> >> +	pr_info("device %d got AER detect notification. uncorrectable error status = 0x%x\n", pdev->devfn, uncor_status);//to be removed
> > 
> > Pls drop this.
> > 
> >>  	mutex_lock(&vdev->igate);
> >>  
> >> -	if (vdev->err_trigger)
> >> -		eventfd_signal(vdev->err_trigger, 1);
> >> +	vdev->aer_recovering = true;
> >> +	reinit_completion(&vdev->aer_completion);
> >> +
> >> +	if (vdev->err_trigger && uncor_status) {
> >> +		pr_info("device %d signal uncor status 0x%x to user",
> >> +			pdev->devfn, uncor_status);
> >> +		/* signal uncorrectable error status to user space */
> >> +		eventfd_signal(vdev->err_trigger, uncor_status);
> >> +        }
> >>  
> >>  	mutex_unlock(&vdev->igate);
> >>  
> >> @@ -1199,8 +1240,33 @@ static pci_ers_result_t vfio_pci_aer_err_detected(struct pci_dev *pdev,
> >>  	return PCI_ERS_RESULT_CAN_RECOVER;
> >>  }
> >>  
> >> +static void vfio_pci_aer_resume(struct pci_dev *pdev)
> >> +{
> >> +	struct vfio_pci_device *vdev;
> >> +	struct vfio_device *device;
> >> +
> >> +	device = vfio_device_get_from_dev(&pdev->dev);
> >> +	if (device == NULL)
> >> +		return;
> >> +
> >> +	vdev = vfio_device_data(device);
> >> +	if (vdev == NULL) {
> >> +		vfio_device_put(device);
> >> +		return;
> >> +	}
> >> +
> >> +	mutex_lock(&vdev->igate);
> >> +	vdev->aer_recovering = false;
> >> +	mutex_unlock(&vdev->igate);
> >> +
> >> +	complete_all(&vdev->aer_completion);
> >> +
> >> +	vfio_device_put(device);
> >> +}
> >> +
> >>  static const struct pci_error_handlers vfio_err_handlers = {
> >>  	.error_detected = vfio_pci_aer_err_detected,
> >> +	.resume         = vfio_pci_aer_resume,
> >>  };
> >>  
> >>  static struct pci_driver vfio_pci_driver = {
> >> diff --git a/drivers/vfio/pci/vfio_pci_private.h b/drivers/vfio/pci/vfio_pci_private.h
> >> index 8a7d546..ba8471f 100644
> >> --- a/drivers/vfio/pci/vfio_pci_private.h
> >> +++ b/drivers/vfio/pci/vfio_pci_private.h
> >> @@ -83,6 +83,8 @@ struct vfio_pci_device {
> >>  	bool			bardirty;
> >>  	bool			has_vga;
> >>  	bool			needs_reset;
> >> +	bool			aer_recovering;
> >> +	struct completion	aer_completion;
> >>  	struct pci_saved_state	*pci_saved_state;
> >>  	int			refcnt;
> >>  	struct eventfd_ctx	*err_trigger;
> >> -- 
> >> 1.8.3.1
> >>
> >>
> > 
> > How about some explanation about what is going on here?  All these
> > changes seem racy since any number of errors can trigger at any time.
> > 
> 
>