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

[Alex Williamson]

On Tue, 10 Jan 2017 17:11:01 +0200
"Michael S. Tsirkin" <mst@xxxxxxxxxx> wrote:

> 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?

This is the same blocking user accesses while the device is in recovery
that you thought was ineffective/wrong before.  Why do we still need it
if QEMU isn't trying to handle fatal errors?  If the kernel is doing a
reset shouldn't the user consider the device dead?  A commit log
explaining this is absolutely necessary.  Thanks,

Alex

> > >>
> > >> Signed-off-by: Cao jin <caoj.fnst@xxxxxxxxxxxxxx>
> > >> ---
> > >>  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.
> > >   
> > 
> >