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

[Cao jin]

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.

-- 
Sincerely,
Cao jin

>>
>> Signed-off-by: Cao jin <address@hidden>
>> ---
>>  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.
>